Thin-film nanocomposite magnets composed of α-Fe- and c-axis-oriented Nd₂Fe₁₄B phases were synthesized by rf magnetron sputtering onto heated glass substrates. X-ray diffraction measurements showed the coexistence of (001)-textured Nd₂Fe₁₄B and randomly aligned α-Fe phases. Magnetization curves showed a single-phase-like behavior, and the values measured with fields applied perpendicular to the film plane were apparently larger than those measured with fields applied along the film plane. These results indicate the exchange coupling between the aligned Nd₂Fe₁₄B and α-Fe phases. As the volume fraction of the α-Fe phase increased from 7% to 40%, the saturation magnetization showed a monotonic increase, while the coercivity decreased from 6.2 to 1.7 kOe. These results were compared with the micromagnetic calculations and the experimental data for randomly oriented Nd₂Fe₁₄B -α-Fe films.

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The microstructure and magnetic properties of nanocomposite Fe₉₃Nb₂Nd₅B₅ alloy produced by crystallization of an amorphous phase were investigated. Melt-spun ribbons form a nanocomposite structure consisting mainly of bcc-Fe, Nd₂Fe₁₄B, and residual amorphous phases after annealing at a temperature of 1023 K. The nanocomposite alloy exhibits improved values of the remanence (J_r), coercive force (H_cJ), and maximum energy product ((BH)_max) after annealing at a higher heating rate (α) in the temperature range corresponding to the primary crystallization temperature of the bcc-Fe phase. The grain sizes of each phase decrease with increasing α. The improvement in the hard magnetic properties brought about by rapid annealing is presumably due to improved homogeneity in the nanocomposite structure.

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Exchange-coupled nano-composite melt-spun powder is a nano-stroctured composite of soft and hard magnetic phases mutually coupled by exchange interaction at the grain boundaries. Its resource balance and resistance to oxidation are better than those of Nd₂Fe₁₄B stoichiometric composition melt-spun powder, because it contains a smaller proportion of rare-earth elements such as neodymium. In order to apply this powder to high-efficiency small IPM (interior permanent magnet) brushless motors, we developed a modified molding technique using the slip-flow mechanism, which allows high-density molding of nano-composite melt-spun powder exceeding 95 wt%. This technique was used to develop a small IPM rotor by directly molding the melt-spun powder with a laminated steel core. IPM motors using the above-mentioned rotor were found to have adequate stability with respect to aging and reverse magnetic fields, as well as high efficiency.

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Isotropic Nd-Fe-B-based ring-shaped resin-bonded magnets have been generally used in small motors and actuators for PCs and their peripherals. However, development of a new type of magnet with superior magnetic properties is essential for a further reduction of the size of such motors. Although usage of anisotropic Nd-Fe-B powder made by the HDDR process is a promising method of preparing anisotropic magnets to replace the conventional isotropic magnets, its high coercivity of over 1.2 MA/m, which is required for thermal stability of the magnetic flux comparable with that of conventional isotropic Nd-Fe-B magnets, makes it difficult to magnetize the prepared magnets. Therefore, magnets prepared from anisotropic HDDR powder have not been used to create ring-shaped magnets for small motors up to now. To overcome the above difficulty, we developed a new technology that makes it possible to prepare axially oriented ring-shaped magnets for small motors. This paper reports a method of preparing axially oriented ring-shaped magnets for small motors from anisotropic HDDR powder. To use this process, it is possible to product an anisotropic Nd-Fe-B-based flexible bonded magnet. These flexible bonded magnets are able to keep a high efficiency, like a radially oriented magnet. And, their magnet powders are covered with elastomer.

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Molecular dynamics simulations of the formation process of Ni/Pd bilayer films were performed by employing the embedded atom method with high (10 eV) and low (0.1 eV) kinetic energies of incident atoms for two different crystal orientations: fcc(111) and fcc(100).
The tendencies of the film formation process and the interdiffusion at the interface were similar in both the (111) and (100) cases. However, the strain at the interface of films on the (100) substrates was larger than that on the (111) substrates.
In the case of Pd deposited on an Ni(100) underlayer, the Pd film grew with the (111) symmetry and partially observed Ni(100)-c(16 × 2) structure. The crystal orientation of the Pd layer varied according to the value of the strain in the Ni(100) underlayer, regardless of the surface condition of that underlayer. In the crystal orientation dependencies, the value of the strain in the magnetic layer at interfaces, which is obtained by simulation, corresponds well to the experimental value of the perpendicular magnetic anisotropy.

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Spin electronic states of wurtzite GaN nanostructres were studied by using ab initio molecular orbital calculations. Two models of pyramidal GaN clusters were constructed with the cluster axes parallel to the crystallographic c axis in the wurtzite. The atom at the apex of the cluster is nitrogen or gallium. We computed the lowest energy spin electronic states, spin densities, static electric fields, highest occupied molecular orbitals, and lowest unoccupied molecular orbitals for both clusters. The spin multiplicities of the clusters were found to be 13 and 3, depending on whether the atom at the apex was nitrogen or gallium, respectively. The GaN clusters were spontaneously spin-polarized in the lowest-energy states. Highly spin-polarized states were induced by the unpaired electrons on the surfaces of the nanostructures.

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The magnetoresistance (MR) of magnetic multilayers. Fe/Cr and Co/Cu, was measured at high pressure. It was found that the effect of pressure on the MR depends on the specimen: the MR of Fe/Cr decreases much more than that of Co/Cu. The large effect of pressure on the MR in Fe/Cr is shown to be due to the suppression of spin-dependent scattering at high pressure. The relation between the effect of pressure on GMR and the interfacial roughness is discussed briefly.

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A huge positive magnetoresistance effect in a relatively low magnetic field (less than 0.5 T) at room temperature was discovered in MnSb granular films. A granular film consisting of nano-scale MnSb clusters was grown on a sulfur-passivated GaAs(001) substrate by molecular beam epitaxy, then covered with an Sb thin layer. The granular film shows magnetic-field-sensitive current-voltage characteristics. When a constant voltage, above the threshold value, is applied to the film, a more than 1000 percent change in the current, which we term a magnetoresistive switch, is driven by the magnetoresistance effect. A possible mechanism for the magnetoresistive switch effect is discussed.

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Polycrystailine La_0.8Ba_0.2Mn_1-xCu_xO₃(x = 0-0.2) was successfully synthesized by using a standard solid reaction method. The crystal structure was shown to change from orthorhombic to tetragonal symmetry at x∼0.1. The magnetization, electric resistivity and MR were studied in relation with Cu doping level. It was also shown that, as x increases from 0 to 0.2, three kinds of MR were observed: spin-tunneling-type MR over the temperature range below T_c, a giant MR due to thermal spin fluctuation at T_c, and ordinary MR due to spin scattering of ferromagnet T_c.

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We formed perovskite magnetic oxide artificial lattices to create novel functional magnetic materials. The magnetoresistance of an (La,Sr)MnO₃/LaFeO₃ superlattice is enhanced by up to 35% in a magnetic field of 1.0 T. In (La,Sr)MnO₃/SrTiO₃ and (La,Sr)CoO₃/(Ba,Ca)TiO₃ hetero-structures, the electrical/magnetic properties of ferromagnetic layers can be controlled by light irradiation and electric field generation, through photo carrier injection and piezoelectric strain effects, respectively.

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We carried out three-dimensional Ising model calculation of Cr-doped manganites LaCr_xMn_1-xO₃, using the Monte Carlo method, to study their magnetization behavior. The magnetic interaction between Mn³⁺ and Cr³⁺ is generally thought to be ferromagnetic, in accordance with the Kanamori-Goodenough rules, whereas our calculation suggests that the magnetic interaction should be antiferromagnetic. These calculation results agree well with the experimental results.

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We investigated the magnetic properties of Cr-doped manganese oxides, LaMn_1-xCr_xO₃ with x = 0.1, 0.2, 0.25, 0.33, and 0.5. All samples showed ferromagnetic insulator behavior. The magnetic characteristics and magnetic circular dichroism measurements revealed that the Cr in ferromagnetic LaMn_1-xCr_xO₃ does not have a magnetic moment in the direction of the magnetization.

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A cross-shaped Co wire on a mesoscopic scale was fabricated by using electron-beam lithography, and the galvanomagnetic effect was measured at room temperature. Many jumps in the Hall resistance were observed. In order to explain these jumps, exchange interactions with the current and voltage probes were considered, and the Hall resistance was calculated. The calculated result reproduced three jumps in the observed Hall resistance. It was found that the Hall resistance curve of a cross-shaped wire can be controlled by the ratio of the coercive forces of the magnetizations of the probes. The magnetoresistance of a narrow wire with two crossing points was understood by using the present model to calculate the magnetization process.

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Fabrication of epitaxial La_1-xPb_xMnO_3-y (LPMO) films with Curie temperatures (T_c) above room temperature (RT) was attempted, using the pulsed laser ablation deposition (PLD) method, as part of a fundamental study for developing multilayered devices that work at RT. X-ray diffraction indicated growth of epitaxial films with a good crystallinity. Films with T_c about 350 K can be prepared under deposition conditions in which the substrate temperature (T_s) is 600°C and the oxygen pressure (P_o) is not less than 0.4 Torr. It was found that the T_c decreased with increasing T_s or decreasing P_o. The decrease in T_c with increasing T_s was shown by electron probe microanalysis to be due to evaporation of lead (Pb) from the film. On the other hand, the decrease in T_c with decreasing P_o was found to be due to decrease of the film’s oxygen content by measurement of He⁺ ion resonant backscattering using (⁴He + ¹⁶O → ²⁰Ne* → ¹⁶O + ⁴He) nuclear resonant reaction.

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The transition metal perovskite oxide SrRuO₃ is well known as an itinerant-electron ferromagnet, while, Sr₂(RuFe)O₆ is an insulator that shows weak ferromagnetism at 140 K.
We made polycrystals of an Sr₂(Ru_2-xFe_x)O₆ (x < 1) system and studied their magnetic and transport properties. As a result, we found that the ferromagnetism disappears at around x = 0.2. At Fe concentrations from x = 0.2 to x = 0.24, the conductivity shows a metallic temperature dependence in the high-temperature region. However, below 200 K, it shows semiconductive temperature dependence. At Fe concentrations over x = 0.25, the conductivity shows a semiconductive temperature dependence in all temperature regions. The metal-insulator transition occurs at around x =0.25 in this system.

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We synthesized polycrystalline materials of a double perovskite system Sr₂Fe(Ru_1-xW_x)O₆ with x = 0.0, 0.2, 0.4, 0.6, 0.8, and 1.0. These materials were made by the solid-state-reaction method, in three types of atmospheres: as-grown in air, annealed in O₂, and annealed in Ar-H₂ (Ar with 1% H₂). From X-ray diffraction and the Mössbauer effect, we found that the samples of Sr₂FeRuO₆ became single-phase after annealing in O₂. On the other hand, single-phase Sr₂FeWO₆ was obtained after annealing in Ar-H₂(Ar with 1% H₂).
The lattice constants showed a monotonic increase from x = 0.0 to 0.8, and Fe had a trivalent state in this region.

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The magnetostrictive properties of Tb_0.5Dy_0.5Fe_2-xM_x Laves phase compounds (M = Co, Ni, Mn, Zn, Cu, Cr) were examined. In various compounds, substitution of Zn and Ni brought about a reduction of the pre-stress dependence on magnetostriction, and the magnetostriction increased to more than 800 ppm in a lower magnetic field of 80 kA/m under a larger compressive pre-stress of 40 MPa. In Tb-Dy-Fe-Zn compounds, which showed the best magnetostrictive properties, changes in the Curie temperature, lattice spacing, and spin re-orientation temperature of the Laves phase were observed with increasing Zn content.

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Organic-inorganic complex magnets ((RNH₃)₂MX₄) were synthesized, where R is a simple alkylammonium molecule (CH₃(CH₂)₁₇), a 1-methy1-naphthalene (C₁₀H₉CH₂), a 1-pro-pyl-naphthalene (C₁₀H₉O(CH₂)₃), or a 1-buty1-naphthalene (C₁₀H₉O(CH₂)₄), M is a 3d transition metal element, and X is a halide element (Cl). Their complexes had a layered perovskite structure checked by XRD. The distance of interlayer space between MCl-based layers was shorter for the complexes with 1-buty1-naphthalene than for those with 1-propy1-naphthalene. When R was a simple alkylammonium molecule, a 1-methy1-naphthalene and a 1-propy1-naphthalene, its Cu complexes showed ferromagnetism and its Mn complexes antiferromagnetism. How-ever, Cu and Mn complexes with a 1-buty1-naphthalene did not show ferromagnetism and antiferromagnetism, respectively. The absorption spectra of Cu complexes were also measured. When R was a simple alkylammonium molecule, a 1-methy1-naphthalene, and a 1-propy1-naphthalene, Cu complexes showed a D_4th structure for inorganic layers, while the structure for the complex with a 1-buty1-naphthalene was D_2d.

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Bcc/amorphous two-phase nanocrystalline samples with various volume fractions of the amorphous phase were prepared from a melt-spun precursor amorphous Fe₉₁Zr₇B₂ alloy. The coercivity of the sample at 77 K, well below the Curie temperature of the intergranular amorphous phase (T_c^am ≈ 370 K), shows a tendency to decrease with increasing the volume fraction of the amorphous phase (V_am). This suggests that the magnetocrystalline anisotropy energy of the sample is diluted by the volume of the residual amorphous phase when the intergranular coupling is stiff. On the other hand, the coercivity at 450 K, well above T_c^am, increases dramatically with increasing V_am. This indicates that the intergranular magnetic coupling above T_c^am depends on the intergranular distance. The stiffness of ferromagnetic coupling in the intergranular region above T_c^am was estimated to be ∼ 10^-14 to 10^-13 J/m². The coercivity at T ∼ T_c^am appears to vary as the - 6^th power of the spontaneous magnetization of the intergranular amorphous phase when V_am is relatively large.

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MnSb ultra-thin films with nominal thicknesses of 0.35, 0.70, 1.05, and 1.40 nm were grown on sulfur-passivated GaAs (001) substrates by molecular beam epitaxy. Atomic force microscopy analyses showed that MnSb formed nanosized dots on the substrate, and that coalescence of the clusters occurred at nominal thicknesses between 0.70 and 1.05 nm. The intensity of the polar magnetic circular dichroism of MnSb clusters and the saturation magnetization suddenly increased when the nominal thickness reached the critical value of 1.05 nm. The coalescence of the dots can be correlated with the sharp increase in the MCD intensity.

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We investigated the magnetic properties of Co-Cr-C/SiO₂ bilayer film, and of Co-Cr-C/Ag/SiO₂, Co-Cr-C/Ti/SiO₂, and Co-Cr-C/Ag/Ti/Si0₂ multilayer films. It was found that a granular Co-Cr-C film annealed at 550°C after deposition on a (10 Å) Ag/(1000Å) Ti/SiO₂ underlayer showed a larger Hc_⊥/Hc_// ratio (the ratio of the perpendicular coercivity Hc_⊥ to the in-plane coercivity Hc_//) than films deposited on (10 Å)Ag/SiO₂ or (1000 Å)Ti/SiO₂ underlayers. This result is considered to be attributable to the fact that the (10 Å)Ag/(1000 Å)Ti/SiO₂ underlayer promotes the orientation of the c axis of hcp-Co grains and increases the perpendicular coercivity of the film.

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Co₉₀Pt₁₀ granular films including plasma − polymerized acetylene were prepared at room temperature by facing − targets sputtering. Their magnetic properties and microstructures were investigated. The coercivity reached 2000 Oe with C₂H₂ partial pressure (PC₂H₂) of 0.07 mTorr or less. The magnetic particles were separated magnetically by plasma − polymerized acetylene at a PC₂H₂ value of 0.07 mTorr with a film thickness of 40 nm or above. The magnetic particle size decreased and the uniformity of particles improved when the film thickness was decreased from 80 nm to 40 nm.

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The Curie temperature (T_c) of magnetite (Fe₃O₄) ultra-fine particles prepared by the co-precipitation method was investigated. The sizes of particles, which are controlled by the ratio of FeSO₄·7H₂O and NaNO₂, ranged from 5 nm to 50 nm. The Curie temperature (T_c) is determined by the relationship M ∼ (1-T/T_c)^β. The temperature (T_c) decreased with the size of Fe₃O₄ particles. It is considered that the Curie temperature can be controlled by varying the size of ultra-fine particles. On the other hand, when the particles were heated at high temperature, the particle size became large on account of the sintering effect. This caused an apparent increase in the Curie temperature.

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Fe₃O₄ (magnetite) films were successfully grown at room temperature by ferrite plating from an aqueous solution of FeCl₂, utilizing Fe²⁺ → Fe³⁺ oxidation realized by adding an aqueous solution of NaNO₂ + NH₃ to the FeCl₂ solution. Since we found that the Fe²⁺/Fe₃O₄ (solid) boundary line in the potential-pH diagram of iron shifts to the higher pH region, we increased the pH of the aqueous solution from 5.0-6.8 (at which previous plating was performed at 60°C-100°C) to 7.7-8.8. This facilitated the formation of magnetite films, which consist of single-phase magnetite, as revealed by X-ray diffraction. The magnitude of the films‘ saturation magnetization is equal to that of bulk samples. The film deposition rate was measured as a function of the pH and the concentration of NaNO₂.

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The effects of substituting Ba ions for Pb ions on low temperature preparation of barium ferrite thin films and on their magnetic properties were investigated. Ba_1-XPb_XFe₁₂O₁₉ thin films were deposited on a fused quartz substrate by an rf magnetron sputtering method. In order to control the composition of the deposited Ba_1-XPb_XFe₁₂O₁₉ films, several sintered BaFe₂O₄ chips and PbO chips were placed on the barium ferrite target. The film thickness was varied between 20 and 250 nm. As-deposited films were post-annealed at temperatures between 500 and 700°C for 5 hours in air.
Ba_1-XPb_XFe₁₂O₁₉ films with Pb content of 0.24 or above were well crystallized by post-annealing at 550°C for 5 hours in air. Ba_0.65Pb_0.35Fe₁₂O₁₉ film, especially, showed excellent magnetic properties, and its grains were small and uniform. As the film thickness of Ba_0.65Pb_0.35Fe₁₂O₁₉ film was decreased, its coercivity increased; its value reached 5.0 kOe at t = 50 nm. Moreover, the Ba_0.65Pb_0.35Fe₁₂O₁₉ film had little interaction between grains and high thermal stability of magnetization.

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The microstructure of BaM thin films, sputter-deposited using on alternate layer deposition technique on both a c-axis oriented ZnO underlayer and a (111) oriented ZnFe₂O₄ underlayer, was investigated using a high-resolution transmission electron microscope (HRTEM). When the films were deposited on the ZnO underlayer, the film had a layered structure of BaM (c-axis orientation) / Ba-Zn-Fe-O / ZnFe₂O₄ ((111) orientation) / Ba-Zn-Fe-O / Zn-Si-O/SiO₂ / Si. This suggests that the BaM layer was formed after the formation of the layered structure of Ba-Zn-Fe-O / ZnFe₂O₄ ((111) orientation) / Ba-Zn-Fe-O / Zn-Si-O / SiO₂ / Si. On the other hand, when films were deposited on the (111) oriented ZnFe₂O₄ underlayer, the BaM layer grew epitaxially on the (111) plane of the ZnFe₂O₄ underlayer, and the formation of transition layers was not observed. These results suggest that the diffusions of Ba, Fe, and Zn ions between the BaM layer and ZnO or Ba-Zn-Fe-O layer occurred easily but was completely suppressed in the ZnFe₂O₄ layer, which resulted in formation of a ZnFe₂O₄ layer that was sandwiched between the Ba-Zn-Fe-O layers when BaM films were deposited on a ZnO underlayer.

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Fe films were deposited by ion beam sputtering using Ar and Kr gases. The sputtering voltage V_s was varied in the range of 900-1800 V. The magnetic properties of the films had a significant relationship with the element used as the sputtering gas. The saturation magnetization 4πM_s was 21 kG for At and 20 kG for Kr. The coercivity Hc took a minimum value of 5 Oe at V_s of 1200 V for Ar.
The energy and the number of energetic particles, such as the sputtered atoms and the recoiled ions bombarding the substrate was calculated by Monte-Carlo simulation in the sputtering system with an amorphous Fe target. The average energy of the sputtered atoms E_Fe was 36-62 eV for Ar and 30-36 eV for Kr. The average energy of the recoiled ions E_R was 200-370 eV for Ar and 60-100 eV for Kr. The difference in energy between these two sputtering gases, which have the different atomic masses, was remarkable. Bombardment with the sputtered atoms and recoiled ions at high energy reduced H_c of the Fe films. The atomic mass of the sputtering gas was an important parameter in determining the properties of films deposited by ion beam sputtering.

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Fe-Ni-N films were fabricated on MgO{100} single-crystal substrates by dc facing-targets sputtering. Structural analysis and magnetic measurement were carried out. The results can be summarized as follows: (1) for the as-deposited (Fe_100-xNi_x)-N films, α' phase with a stoichiometric N content of 11 at% can be formed up to x = 10; (2) the phase decomposition temperature T_p.d. of α'-(Fe_100-xNi_x)₁₆N₂(x=0-10) depends strongly on the Ni content of the film. The T_p.d. of α'-(Fe_100-xNi_x)₁₆N₂ decreases from about 200 °C(x=0) to about 50 °C(x=10) with increasing Ni content; (3) the formation at R.T. of stable α''-(Fe_100-xNi_x)₁₆N₂(x=5-30) in the Fe-Ni alloy system is concluded to be difficult; and (4) judging from the dependence of the saturation magnetization for α'-(Fe_100-xNi_x)₁₆N₂ on the Ni content, the saturation magnetization of α'-Fe₁₆N₂ is 220 emu/g.

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In order to clarify the correlation between ferromagnetic resonance (FMR) linewidth and structural inhomogenity, the FMR linewidth for 80NiFe(Py) thin films with various buffer-layer materials and thicknesses was measured. Py thin films (40 Å) were fabricated by sputtering on 7059 glass substrate with various buffer layers: Cu, Pt, Pd, and Ta. The out-of-plane angular dependence of the FMR was analyzed using a model that takes account of Gilbert damping of spin precession, the distribution of the effective demagnetization, and the local fluctuation of the angle between the normal direction of the Py film and the external magnetic field. The fluctuation of the angle increased with increasing average roughness (R_a) of the surface on buffer layers measured by AFM, and was therefore, considered to be due to the waviness of the Py layer.

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The induced anisotropy in thin Ni₇₉Fe₂₁ films was investigated. The value of the induced anisotropy field H_k was found to decrease as the film thickness decreased, particularly below 20 nm, even after an adequate annealing procedure with a magnetic field. The value of H_k at 3 nm was found to be nearly half that at 200 nm. Almost the same thickness dependence of H_k was found to exist in both Ni₇₇Fe₂₃ and Ni₈₁Fe₁₉ films, except for slight differences in the absolute magnitude of H_k, depending on the composition. A series of CoZrNb amorphous films showed a qualitatively similar thickness dependence of H_k. On the other hand, the easy axis of the Ni₇₉Fe₂₁ films thinner than 20 nm was switched to the field direction by annealing with a magnetic field perpendicular to the easy axis of the as-deposited films, even at a low annealing temperature of 220°C. The absolute values of H_k in the 3 and 5 nm films after annealing were nearly as large as in the as-deposited films. It is likely that the rearrangement of atom pairs can easily occur in the surface region, resulting in the switching of the easy axis to the annealing field direction in very thin films.

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The extraordinary Hall effect in Fe-Pt thin films prepared by the ion-beam sputtering method was investigated. The Hall resistivity ρ_H at room temperature of disordered samples was larger than that of ordered samples in the composition range of 40 - 80 at% Pt. Disordered polycrystal line samples show a maximum ρ_H value of 3.6 μΩ·cm at a composition of around 60 at % Pt. The influence of the film thickness d on the Hall effect was also investigated. The Hall voltage V_H increases with decreasing d, and a V_H value of more than 100 mV was obtained at d = 25 Å. The saturation field H_k of the perpendicular magnetization decreases with decreasing d, which is considered to be attributable to the surface anisotropy.

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Ferromagnetic MnSb films were fabricated on Si(100) and (111) single crystal substrates by dc planar sputtering. The effects of the substrate temperature and bias on the epitaxial growth are discussed. The main findings are as follows: (a) MnSb grains grown at T_sub. < 170°C were (110) oriented irrespective of the crystal planes of the Si substrates; (b) MnSb grains with (101), (102), and (001) orientations existed in films prepared at T_sub. > 170°C on Si(100) substrate; (c) MnSb grains epitaxially grown on Si(111) substrate were (101)-oriented at T_sub. = 200°C and (001)-oriented at T_sub. = 250°C; (d) in the sputtering method used, the substrate voltage changed from 0 to - 200 V, corresponding to a change in the ion assist energy from 0 to 40 eV/atom; and (e) the use of an ion assist of 15 eV/atom to Si(111) substrate decreased the epitaxial growth temperature of MnSb(001)-oriented grains from 250°C to 200°C.

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The suitability of multi-wave X-ray reflectometry, in which X-ray reflectivities measured with multiple X-ray waves are optimized simultaneously by the least squares method, was investigated for layered structure analysis of spin-valve films. It was found that Co-K_β, Cu-K_β, and Cu-K_α1 lines are suitable for analysis of a spin-valve film based on estimation of the reflective intensity at each boundary of the film. Next, a 3-wave method using these 3 X-rays and a 2-wave method using Co-K_β/Cu-K_β or Co-K_β/Cu-K_α1 lines were examined. Structural parameters such as the film thickness, density, and interface width can be determined more accurately for both the 3-wave and 2-wave methods than for a 1-wave method using the Co-K_β line. In 3-wave reflectometry, the errors, defined as 3 times the standard deviation, in determining the film thicknesses for ∼1 nm CoFe and ∼2 nm Cu films were ±0.04 nm and ±0.02 nm, respectively. The errors in 2-wave reflectometry were slightly larger, being around ±0.05 nm.

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Magnetization processes in microfabricated NiFe wires were observed by using a Kerr microscope equipped with an oil-immersion lens (NA = 1.3) and an Hg lamp. NiFe wires 20 nm in thickness were prepared by using lift-off techniques. The width (W) of the wires was designed as 0.5, 1.0 and 2.0 μm and the length (L) as 50 μm. One end of the wire was connected to a square-shaped head with a side of 2 W, which was designed to act as a domain wall source. In each wire, necks of different widths were introduced as artificial pinning sites of a domain wall. Magnetization reversals in very narrow wires with 0.5 μm width were clearly observed. It was confirmed that domain wall penetration, pinning, depinning, and also the direction of wall motion can be controlled by using square-shaped head and necks with optimized width. The Kerr microscope image with the domain wall near the neck is almost consistent with the Kerr effect image obtained by micromagnetic calculation.

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Spin-valves using epitaxial orthoferrite (YFeO₃) as an antiferromagnetic layer were prepared on SrTiO₃(100), (110), and (111) substrates, and their properties were investigated. Each spin-valve showed a markedly different MR property according to the plane of the SrTiO₃ substrate. The highest MR ratio was observed in a spin-valve with a-axis-oriented epitaxial YFeO₃ on the SrTiO₃ substrate with a (110) plane, while a trace amount of MR was visible in a spin-valve with c-axis-oriented YFeO₃ on (100) SrTiO₃. The MR properties of the spin-valve on (110) SrTiO₃ exhibited strong angular dependence under an in-plane magnetic field. The exchange coupling in these spin-valves seems to have some relation with the direction of parasitic ferromagnetism in the antiferromagnetic epitaxial YFeO₃ layer.

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We observed hysteresis loops of resistance in GMR and TMR films using GdFe alloy with perpendicular. The MR ratio of GMR film was approximately 0.036% when the thickness of Cu film was 4 nm. Al₅₀Cu₅₀ film with a surface roughness of approximately 0.2 nm was used for the under electrode of TMR film. The Al₂O₃ film was prepared by direct deposition on an Al₂O₃ target, and atomic ratio O/Al of the Al₂O₃ film was 1.52 according to an RBS analysis. The MR ratio of TMR film was approximately 0.95% when the thickness of Al₂O₃ film was 2.2 nm.

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Submicron-size wires of Co-Al-O granular film were fabricated using a gallium focused ion beam, and the magnetoresistance (MR) of the wires was investigated. Bias voltage dependence of the MR for Co-Al-O films was measured up to 60 mV utilizing a wire geometry with cross-sectional area of 100×100 nm² and length of 500 nm. MR is constant in the range of V_b = 0 to 60 mV at 77 K, where V_b is defined as the bias voltage between two neighboring Co granules in the wire, but the MR magnitude is slightly smaller than that before fabrication by the focused ion beam. The decrease in MR is thought to be caused by an irradiation effect of high-energy gallium ions.

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The properties and structure of (Fe, Co)-Mg-F films, prepared by a tandem deposition method using rf sputtering apparatus, were studied. These films show granular-type TMR properties, and the MR ratio at 10 kOe of 42 vol.% Fe-Mg-F film is 7.8%, which is about twice large as that of Fe-Al-O film. The ρ values of the (Fe, Co)-Mg-F films are 10²-10⁴ times larger than that of (Fe, Co)-Al-O films. (Fe, Co)-Mg-F films have a nano-granular structure composed of metallic granules with a diameter of 2-3 nm and thin insulator boundaries; this structure is almost the same as that of (Fe, Co)-Al-O and other metal-oxide nano-granular TMR films. However, the insulator boundaries of (Fe, Co)-Mg-F films are formed from crystalline phase, while the structure of the boundary is amorphous phase in the case of metal-oxide-type nano-granular films.

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Tunnel magnetoresistance (TMR) in double tunnel junctions with layered ferromagnetic nanoparticles was investigated. The sample comprised two ferromagnetic electrodes (CoFe/Fe) separated by an Al₂O₃ insulating layer in which a layer of Co₈₀Pt₂₀ nanoparticles was embedded. The nanoparticles were ellipsoidal with an average diameter of 3.7 nm, and composed a well-defined layer. The TMR and the tunnel resistance of the sample showed steep increases around 100 K, and weak temperature dependence below 50 K. The zero-bias TMR rose from 1 % at room temperature to 18 % at 20 K. Below 20 K, we observed magnetoresistance oscillation with respect to the bias voltage. The observed TMR oscillations, with periods of 1.6 and 15 mV, accompanied oscillations of the conductance. We consider that the conductance oscillations may originate from the coexistence of the discrete energy level of the nanoparticles and the discrete electrostatic potential due to the single-electron charging effect.

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We observed scanning tunneling microscopy (STM) topographic images for structure characterization and measured current-voltage (I-V) spectra (scanning tunneling spectroscopy: STS) for the investigation of single-electron tunneling in Co-Al-O granular thin films with various Co concentrations. The size of Co granules increases with the Co concentration. The STS results indicate the appearance of a Coulomb staircase with a single period at room temperature. The period of the Coulomb staircase depends on the Co concentration. When the Co concentration increases, the charging energy of granules decreases because the granule size increases. Consequently, the period of the Coulomb staircase decreases with increasing Co concentration.

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Tunnel magnetoresistance and spin polarization in (Ni-Co)/Al₂O₃/(Ni-Co) tunnel junctions are studied in the framework of the linear response theory. The multi-orbital tight-binding model is used to take account of the realistic band structure of the ferromagnets. The results show a small negative spin polarization and a magnetoresistance ratio of less than one percent. It is argued that the electronic structure of Al atom oxidized incompletely at interfaces is the origin of the positive spin polarization and the large magnetoresistance ratio.

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Tunnel conductance and magnetoresistance in tunnel junctions with amorphous insulating barriers are studied by numerical simulations based on the linear response theory. The effects of the disorder within the barrier on the tunnel conductance and magnetoresistance are clarified.

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Ferromagnetic tunnel junctions of Ta/Al/Ta/Ni₈₀Fe₂₀/IrMn/Co/Al-oxide/Co/Ni₈₀Fe₂₀/Ta/Cu with various Al-oxide thicknesses were fabricated by rf magnetron sputtering and ICP oxidization. The thickness of Al was varied from 6 Å to 13 Å. With decreasing thickness, the tunnel resistance decreased from 3 x 10⁵ Ω·μm² to 1.2 x 10²Ω·μm². At Al thicknesses of 13 and 10 Å, the MR ratio was 22%-20%, and increased to 35%-30% after annealing. In other junctions, the MR ratios were small and increased only slightly after annealing, the I-V curves of all junctions were asymmetric before annealing. The curves were analyzed by taking account of both barrier heights φ₁ and φ₂ (upper and lower interfaces). The difference between φ₁ and φ₂ was reduced by annealing, and the MR ratio became large at φ₁ = φ₂.

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Ni-Fe/Co/Al-O/Co tunnel junctions with small active areas down to 3 x 3 μm² were fabricated by the micro-fabrication technique. The Al-O insulating layer was prepared by plasma oxidation of a thin sputtered Al film. The dependences of the tunnel magnetoresistance on the thickness of the Al film and the oxidation time were investigated. The interface structure of the junction was observed by using high-resolution electron microscopy. The relationship between the magnetoresistive properties and the interface structure is discussed.

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The effect on the tunneling magnetoresistance (TMR) of inserting the nonmagnetic metals (NMs) Al, Cu, and Ta between the insulator and ferromagnetic layer of a tunnel junctions was investigated. The TMR ratio for a junction with Ta decreased rapidly with increasing Ta thickness, while that for a junction with Al remained more than 50 Å of the thickness. From cross-sectional TEM and AFM measurement, it was found that a junction with thick Al has an insulating layer on both sides of the metallic Al; that is, it would be a double-barrier tunnel junction. We compared the experimental result for the metallic Al thickness dependence of the TMR ratio with the theory of double tunnel junctions. Consequently, the spin diffusion length of Al was estimated to be sub-micrometer.

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Oxides of Al_1-xCo_x (x = 0, 0.25, 0.50, 0.75, and 1.0) alloys were chosen as barrier materials in this work. The tunnel junctions consisted of a bottom electrode Al_1-xCo_x and a top electrode Al with an insulating layer {Al_1-xCo_x-oxide} formed by natural oxidation in a baking-box at 333 K. The oxidation time for forming an Al_1-xCo_x-oxide layer on the surface of the bottom Al_1-xCo_x layers was optimized. When tunnel resistances were between 10⁵ and 10⁷ Ωμm² measured at 1 mV and at 4.2 K, the effective barrier height and width of the insulating layers of Al_1-xCo_x-oxide (x = 0.25, 0.5, and 0.75) varied between 0.7 and 2.2 eV and between 1.4 and 1.7 nm, respectively. It is shown that the thin oxide layer of Al_1-xCo_x alloys can be used as a barrier.

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The relationship between Co_xFe_1-x(X= 100, 90, 75, 60, 50) and the tunneling magnetoresistive effect was investigated. Co_xFe_1-x, which have high saturated magnetization, were selected as the ferromagnetic materials. The fabrication process was successful in a TMR junction with large MR ratio. The maximum MR ratio for Co₇₅Fe₂₅ junctions yielded 40.7%. The MR ratios for Co₇₅Fe₂₅ junctions were almost constant as a function of the junction area, which meant an MR ratio over 40% didn't contain a geometrically enhanced MR effect. V_h, defined as the point where the TMR decreased to half its 1mV bias value, lay between 360 and 455 mV. The bias dependence of TMR was related to barrier height in all Co_xFe_1-x junctions. As barrier height increased, weaker bias dependence was obtained.

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The local electrical properties were measured simultaneously with the topography for a Ta(50Å)/Fe₂₀Ni₈₀(50Å)/IrMn(150Å)/Co(50Å)/Al(d_AlÅ)-oxide junction. The electrical image showed the contrast with a lateral size of around a few nm, and no strong correlation with the topography was observed. By analyzing the local current-voltage characteristics, we found that the contrast of the current image showed the distribution of the barrier height. This may be due to the lack of the oxygen from the stoichiometry of the Al₂O₃ composition. We measured the current images for junctions with shorter oxidation times and with lower Al thicknesses. The histogram of current densities was calculated by taking into consideration the Gaussian distribution of the barrier height. It fitted the experimental results well except for the junction with thin Al; this may be due to a local leakage current. The tunneling magnetoresistance (TMR) ratio was considered to be reduced by this current.

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Inelastic-electron-tunneling spectroscopy (IETS) was used to investigate the electron states of the Co/Al(d_Al)/Al-oxide/Co interface in ferromagnetic tunnel junctions. The IET spectra for both parallel and anti-parallel magnetization configurations of ferromagnetic electrodes showed a strong positive peak for d_Al = 0 Å. The subtraction spectrum defined by the difference between the spectra of the two configurations was calculated. The subtraction spectrum indicates only a magnon-assisted inelastic tunneling process. The tendency of the tunneling magnetoresistance (TMR) ratio to decrease with bias voltage agreed with the shape of the subtraction spectrum. By assuming surface magnon inelastic excitation, we obtained the distributions of correlation length and Curie temperature for both ferromagnetic electrode surfaces on the insulator. If an Al layer was inserted between a ferromagnet and an insulator, the subtraction spectrum showed an asymmetry to the bias voltage and magnon inelastic excitation at the interface decreased.

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Fe_3-xO₄ films prepared by ferrite plating exhibited negative magnetoresistance associated with spin-dependent intergranular transport. The Fe_3-xO₄ plated films were composed of Fe₃O₄, γ-Fe₂O₃, α-FeOOH, and γ-FeOOH. We investigated the relationship between the concentration of NaNO₂ in the oxidizing solution and annealing, and the degree of oxidation, magnetic properties, and current-in-plane (CIP) electrical properties. Resistivity was about 0.3-500 μcm, which is higher than that of bulk magnetite (10^-2 μcm). MR ratios taken in the maximum field of 2.5 kOe increased as much as 5.7% with increasing concentrations of NaNO₂. Mössbauer spectroscopy and electrical evaluation showed that an increase in Fe³⁺ ion content, in other words, an increase in insulating region, raised the resistivity and the MR ratio with increasing concentrations of NaNO₂. The temperature dependence of the resistivity suggested that the magnetoresistance is caused by spin-dependent tunneling through the insulating region that existed in the grain boundaries.

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