Research has been done on various ways of reducing noise in the fabrication of thin-film magnetic recording media. Our approach is based on simultaneous sputtering of SiO2 and Co-Pt on a Cr underlayer at high Ar pressure and at room temperature. The resulting film was composed of fine magnetic grains less than 10 nm in diameter, isolated from each other by SiO2-rich regions. These fine magnetic grains formed clusters with a diameter of about 30 nm, which grew on top of single Cr columnar grains and were spatially separated from other clusters. The angular dependence of the coercivity suggested that these clusters were more magnetically isolated from each other, with a more coherent magnetization mode, than films deposited at a lower Ar pressure atmosphere or films not composed of SiO2. As a result, our film displayed lower noise characteristics.
Magnetoplumbite-type Ba ferrite (BaM) layers were deposited on ZnO (002) and Pt (111) underlayers by using a facing-targets sputtering apparatus in a gas mixture of Ar, Xe, and O2 at various substrate temperatures Ts. A Ba ferrite layer as-deposited on a ZnO underlayer at Ts values above 475°C and one as-deposited on a Pt (mmm) under-layer at Ts values above 500°C revealed clear c-axis oientation. The saturation magnetization 4πMs was 5.1 kG and 4.0 kG for ZnO and Pt underlayers, respectively. Both underlayers exhibited high perpendicular coercivity Hc⊥ and low in-plane coercivity Hc// of about 2.4 and 0.2 kOe, respectively. A Ba ferrite layer deposited at a relatively low Ts of 300°C and annealed at 800°C in air also revealed excellent c-axis orientation and exhibited a relatively low perpendicular coercivity Hc⊥ of 0.6 kOe. A clear di-pulse was observed for the isolated wave form of a BaM/Pt film as-deposited at Ts of 600°C owing to the perfect perpendicular magnetization orientation, and a relatively high linear recording density D50 of 123 kFRPI was achieved.
The effects of third additive elements on the surface and volume perpendicular magnetic coercivity of Co-Cr alloy films were studied. The difference of surface and volume coercivities between the coercivity thickness dependences in Co-Cr-Ta and Nb films is discussed. It is clearly shown that the Co-Cr-Nb film shows almost the same tendency in the thickness dependence of both surface and volume coercivity. It is concluded that Co-Cr-Nb films are superior to Co-Cr-Ta in term of magnetic coupling in the film thickness direction, exhibiting a high crystallinity and a high crystal orientation.
The effect of the medium thickness in perpendicular magnetic recording on double-layered media is discussed. It was found that the thickness of the medium significantly affected the recording capability of the medium. By improving the coercivity of medium, we obtained high flux density on the surface of a comparatively thick medium.
The recording characteristics of single- and double-layer perpendicular media without and with a thin soft magnetic backlayer were investigated by using merged MR heads. In single-layer media, even a thin soft back-layer with a thickness of 10 nm increased the low-density output and the overwrite property by nearly 4 dB at magnetic spacings of less than 47 nm. In double-layer media with a 10-nm-thick backlayer, no degradation of the recording density was observed.
An abnormal reproduced waveform was observed in spin-valve (SV) heads. We show that this abnormal wave-form was caused by instability of the pinned-layer magnetization even below the blocking temperature (Tb). In SV heads with an NiO/CoO-bilayer (NiO/CoO-SV heads), the pinned-layer magnetization is easily aligned to the track width direction and becomes unstable even at room temperature. FeMn-SV heads showed a relatively stable wave-form, in contrast to NiO/CoO-SV heads. However, below a temperature of 100°C, the pinned-layer magnetization reverses and is pinned easily to the direction of the applied current field. On the other hand, the pinned-layer magnetization in NiMn-SV heads is highly stable, mainly because of the high Tb.
The dual spin-valve (DSV) has an MR ratio 1.5 to 2 times more than that of a conventional spin-valve. We investigated the MR properties of a DSV with PdPtMn antiferromagnetic layers, which showed high corrosion resistance and high thermal stability. The magnetization of the free layer is rotated from the easy axis by the magneto-static fields of the two pinned layers. We examined the dependence of the bias field (Hb) on the DSV structure, reducing the pinned layer thickness to decrease the magneto-static field, reducing the Cu spacer thickness to increase the interlayer coupling, and varying the magnetic field generated from the sense current. We succeeded in decreasing the bias field to half that of a symmetric DSV by introducing a thin pinned layer, a thin Cu spacer and an asymmetric DSV.
The output fluctuations of magnetoresistive (MR) heads with abutted permanent magnets were analyzed by micro-magnetic simulation. The longitudinal bias field was calculated from the magnetization configuration of the permanent magnet (PM) film. The output fluctuation of the MR head was simulated by using the longitudinal bias field, which was calculated with various interface structures between the MR and PM films. When the PM film covered the track edge of the MR capping layer, the longitudinal bias field near the track edge was locally reduced. The local reduction of the bias field was caused by an extra field generated by a charge appearing at the edge of the region where the PM film overlaps the capping layer. It is proved that an MR head with a PM film covering the edge of the capping layer shows output fluctuation, whereas the output is stable when the PM film does not cover the capping layer.
The insulating properties, internal stress, and film structure of Si-O-added Al-O films, and their etching characteristics when immersed in water, were investigated to determine their suitability as shield MR head materials for high-density magnetic recording. The films showed good insulating properties, low internal compressive stress, and excellent corrosion resistance in water. It is concluded that the Si-O-added Al-O films with thicknesses of up to 50 nm should be adopted to reduce the thickness of gap-insulating film.
A contact SCC-MIG head with three contact pads was prepare by using the dry etching process, and its read/write performance was evaluated. The magnetic spacing of the contact system was estimated to be about 30 nm and the bouncing height was 10 nm. A D50 of 250 kFCI was achieved by using a gap length of 0.10 μm and a track width of 1.2 μm. The read/write performance can be theoretically improved by reducing the overcoat thickness and/or optimizing the magnetic properties of the medium. Regarding the gap length dependence, the read/write performance was significantly improved by using a small gap length in applications involving narrow magnetic spacing, such as contact recording.
In a previously developed double-laminated Fe-based alloy film head, it is thought that local permeability deterioration around the magnetic gap causes disagreement between the actual output and the value estimated from the permeability observed in the solid film. Accordingly, a new double-laminated Fe-based alloy film was developed, making full use of the techniques of double lamination, anisotropy modulation control, and magnetostatic coupling. No severe deterioration of the film‘s permeability caused by its shape factor was observed. The bulk head using this film exhibited higher reproduction output in a wider frequency range without any frequency ripples, resulting in a 7 dB output improvement at 28 MHz over a conventional laminated head using Co-based amorphous alloy film.
The write field distributions of merged MR heads and the magnetization of longitudinal magnetic recording media were investigated by using a three-dimensional simulator. The recording performance of a leading-pole trimmed merged MR head (head-2) is compared with that of a conventional merged MR head (head-1). The write field of head-2 decreases more sharply at the track edge than that of head-1. The magnetization pattern recorded by using head-1 shows track edge hooks; however, fewer hooks were recorded by using head-2. It is confirmed that the effective track width (ETW) recorded by head-2 at a low linear density is narrower and the linear density dependence of the ETW is smaller than in head-1. The phase shift of the output wave recorded by head-2 in the off-track position is smaller than that of head-1. The D50 of head-2 is higher than that of head-1.
We fabricated a novel single-pole head on a flying slider for perpendicular magnetic recording. By using three film-conductors to energize a main pole at its end, a high recording sensitivity of 0.03 ATP-P and a very low inductance around 10 nH were obtained. A D50 value of 135 kFRPI was confirmed, almost the same at that of a bulk coil songle-pole head in sliding contact recording. This head provides an idea of a practical single-pole head for a double-layered perpendicular medium for high-frequency applications.
In measurements of time decay in perpendicular double-layered media, a large output decay was observed when a regular single-pole head was used for both writing and reading. Investigation of this phenomenon revealed that the demagnetization of the media was caused by the instability of the domain wall of the main pole film and stray field concentration by the main pole during the reading process. Several countermeasures were proposed.
The noise characteristics of obliquely oriented Co-O thin-film tapes are investigated in relation to the magnetic properties of the tapes. The contribution of the transition noise, which is caused by the irregularity of the magnetic transition region, increases with the squareness ratio of the tape, owing to the large magnetization components in the longitudinal direction. With more perpendicularly oriented tapes, the transition noise is almost negligible, while larger film thickness is necessary to compensate for the output reduction at very low linear densities, resulting in increased non-transition noise. In larger-squareness tapes, the transition noise reduces the C/N ratio in the wavelength region of around 1 μm, although in the shorter-wavelength region, the tapes exhibit a higher C/N ratio than more perpendicularly oriented tapes, owing to the higher output.
In MR heads, read-nonlinearity and write-nonlinearity, which is manifested in phenomena such as nonlinear transition shift (NLTS), degrade the bit error rate (BER) performance in a PRML read channel. We discuss a simple method of estimating these nonlinearity effects for a PRML read channel, and compare the calculated and experimental results. In a PRML read channel, the BER can be easily calculated from the noise deviation after the equalization, and the nonlinearities increase the noise deviation. The calculation and experimental results show a proportional relationship between the noise deviation due to read nonlinearity and the absolute value of the amplitude asymmetry. The deviation due to NLTS can be calculated by considering the first and second adjacent transition shifts and write precompensation. The total effects of the nonlinearities are easily calculated by adding the squares of all the noise deviations.
The error rate performance of MR heads with tracking servo was investigated. The bathtub curves and the position error signal (PES) were computed by using the cross-track profile estimated by micromagnetic calculation. As the read-track width becomes smaller, the linearity of the PES becomes worse and the off-track tolerance from bathtub curves increases. Consequently, the error rate performance with tracking servo increases. As the track pitch becomes smaller, both the linearity of the PES and the error rate improve.
A submicron track width of 0.4μm was observed by measuring an MFM image with a combination of a single-pole head and a perpendicular double-layered medium. Because of its sharp head field distribution, this combination is considered capable of obtaining a very narrow track-pitch. By measuring the off-track overwrite profiles with a thin-film single-pole flying head, we found that the erase band width was around 25 nm, which was acceptable for merged MR head and perpendicular double-layered medium.
This paper describes the magnetic and electromagnetic wave absorption properties, from 1 to 20 GHz, of M-type hexagonal ferrites, in which Fe3+ is replaced by (Ti0.5M0.5)3+ (M = Co, Ni, Zn, Mn, Cu). Samples were prepared by a conventional powder metallurgy method. These ferrites exhibited good microwave absorption properties in the X-band range (8-12 GHz), and the maximum reflection loss was calculated to be between - 20 and - 50 dB. In the case of M = Mn, high μ'' values were obtained, which allowed the matching thickness to be reduced to 0.58 mm. It is possible that these M-type ferrites may find applications as microwave absorbers in the X-band range.
Tri-layered films composed of magnetic garnet Bi, Ge, Co:DyIG, highly Ga-substituted Bi:DyIG, and Bi, Ga:DyIG layers were deposited by the pulsed laser ablation (PLA) method, and their magneto-optical properties were investigated. The first and third magnetic layers in the tri-layered film showed the different Faraday rotation spectrum in the short-wavelength region from 400 nm to 700 nm. The Faraday rotation of the Bi, Ge, Co:DyIG and Bi, Ga:DyIG films had maximum values for wavelength of around 435 nm and 490 nm, respectively. The coercivity (Hc) and Faraday rotation of the Bi0.31Dy3.0Ge0.32Co0.36Fe4.01O12 film showed nonlinear dependence on the annealing temperature (Ta), and Hc reached a value of 7 kOe at Ta = 860°C. The same film annealed at Ta=880°C showed a compensation temperature near room temperature.
Magneto-optical polar and longitudunal Kerr effects in bcc-Fe (001) epitaxial films sandwiched between Au (001) layers were studied for Fe thicknesses dFe = 3-1000Å in the photon energy range of 1.55-6.2 eV. The polar Kerr rotation peaks related to quantum well states (QWS) fomed in Fe layer disappeared above dFe=20Å. In films with dFe≥100Å, the polar Kerr spectra above 3.5 eV were substantially the same as the spectrum of bulk Fe. Below 3 eV, on the other hand, a Kerr rotation peak enhanced by the plasma edge of Au at 2.5 eV shifted to the lower energy side with the increase of dFe even above 100Å, and the intensity of the pear exceeded the bulk value around dFe = 100Å. In the longitudinal Kerr rotation spectra the peaks related to QWS appeared nowhere in the whole range of dFe. This suggests that the contribution of QWS to the off-diagonal complex dielectric tensor element responsible for longitudinal Kerr effect is in our Fe films negligible.
The magneto-optical (MO) Kerr effect for MnSbPt films with a giant magnetic Kerr rotation was investigated in connection with the microstructure. The results revealed that (1) the PtMnSb phase with fcc structure coherently precipitated at the grain-boundary of the matrix MnSb phase with hcp structure after annealing in the range from 200°C to 300°C, (2) both the MnSb phase and the PtMnSb phase were recrystallized after annealing in the range from 300°C to 400°C, (3) the PtSb2 phases nucleated and grew to be dendrite as a result of the diffusion of Pt atoms from the PtMnSb phase after annealing at over 400°C, and (4) the change in the MO Kerr effect for MnSbPt films annealed at over 300°C corresponded to the decrease in the volume-ratio of the PtMnSb phase to the MnSb phase, owing to the formation and growth of the PtSb2 phase.
The mechanism of the enhancement of the MO Kerr rotation for Mn50Sb44Pt6 film was investigated from the view-points of the phases and their components of the dielectric tensor. As a result, it was found that after annealing at 300°C, (1) for (MnSb)50-0.5xPtx (x < 14 at%) films, the PtMnSb phase made a larger contribution to the ε'xx spectrum than would be expected from the Pt concentration, (2) concerning the ε'xy at 2.3 eV and 4.7 eV, where the PtMnSb phase showed ε'xy structure, with increasing Pt concentration x along the line of (MnSb)50-0.5xPtx, the value of ε'xy at 4.7 eV decreased monotonously, but the value of ε'xy at 2.3 eV was maximum at x=17at%, and (3) for the Mn50Sb44Pt6 film, the maximum of θK, where ε'xx was relatively small, was originated from ε'xy.
The structure and magneto-optical properties of MnPt3/CoPt3 superlattices grown at R. T., 300°C, and 500°C were investigated. The formation of a layered structure in the superlattices was confirmed by X-ray measurements. The structure of the sample grown at room temperature was disordered fcc. The Kerr spectrum of this sample was similar to that of a Co25Pt75 disordered alloy. The structure of the sample grown at 300°C was a mixture of the Cu3Au and CuAu types. The Kerr spectrum showed peaks at 1.3 eV and 4.0 eV, which correspond to the peaks for the MnPt3 ordered phase and the Co25Pt75 disordered alloy, respectively. The structure of the sample grown at 500°C was of the Cu3Au type. The Kerr spectrum is similar to that of an MnPt3 ordered alloy.
A novel technique for designing magneto-optical films is presented: the algorithm, which automatically determines the multilayer structures of films with designated optical and magneto-optical properties, is regarded as an extension of the genetic algorithm. The film properties are designated by a simple fitness function f (x), and the film structure that maximizes f (x) is chosen as the optimum one. The present technique has been used to determine two kinds of film structure: one exhibits the largest Faraday rotation θF and the other exhibits high transmissivity T and large θF simultaneously. These films were obtained after the evolution of about 2000 generations: in one, T=29% but θF = -28 deg/μm at λ = 1.15μm, while in the other, T = 70% and θF = -16 deg/μm at the same wavelength of light.
We measured the Faraday rotation (FR) spectra (λ = 500-800 nm) in granular films of Ni/PVC (prepared by spin-coating polyvinyl chloride containing Ni fine powders of ∼20 nm diameter) and (Fe or Co)/SiO2 (prepared by RF-diode co-sputtering and annealed at 400-900°C). The FR spectrum in the Ni/PVC films was best-fitted by assuming that the volume fraction f of Ni is 0.27, though analysis resulted in f = 0.11, suggesting that the FR is enhanced; a possible explanation is “weak localization of light“ in the granular structure. The FR in the Fe/SiO2 and Co/SiO2 granular films increased as the annealing temperature (Ta) was raised, reaching a maximum followed by a decrease. The maximum FR was, however, much smaller than that calculated for the films, probably because the size of the metal particles became comparable with the wavelength of light.
Large magneto-optical properties are highly desirable in isolators and such devices. Recently, magneto-optical Faraday effects have been greatly enhanced by localization of light and use of the nonlinear magneto-optical Kerr effect. This paper describes cases of the enhancement of magneto-optical effects: (1) the case in which ultra-fine magnetic particles are used; (2) the case in which localization of light is used, and (3) the case in which a grating is used with a magnetic thin film. The enhancement of the magneto-optical effects in these three cases is over 50 times that in other cases. The total rotation angle 34 degrees at 10 kG with a 100-nm magnetic thin film.
The optical properties of Cd1-xMnxTe magneto-optical waveguides grown on GaAs substrates were studied. The insertion of buffer layers of 2-nm-thick ZnTe and 1 -μm- thick CdTe between the substrate and Cd1-xMnxTe layers improved the crystalline quality of the waveguides, and reduced the optical loss. Use of a smoothing Cd1-zMnzTe layer between the Cd1-xMnxTe core layer and Cd1-yMnyTe clad layer was also effective in reducing the optical loss. Optical losses of 11 dB/cm, 26 dB/cm, and 88 dB/cm were obtained for wavelengths of 1150 nm, 784 nm, and 633 nm, respectively, for Cd0.55Mn0.45Te waveguides.
Magnetic domain expansion readout is studied without the presence of an alternative magnetic field. The reproduced waveform of a crescent-shaped domain 0.08 μm in length reaches 70% of the saturated signal level. However, a circular domain of 0.3 μm diameter does not expand so much. In the case of crescent domain expansion, it is considered that the copied domain shape is different from the original crescent shape in the recording layer, and that this reduces the magnetic energy. The assumption that the copied domain shape of the expansion layer becomes circular agrees well with the experimental result for the domain expansion ratio.
Recently many types of magnetically induced super-resolution (MSR) have been proposed for high-density recording on magneto-optical (MO) disks. Among them, double-mask rear-aperture detection (D-RAD) is the most promising, because of its high resolution and its crosstalk advantage. However, D-RAD requires a high external magnetic field for MSR readout. We investigated MSR by D-RAD in order to reduce the readout magnetic field. By optimizing the structure of MSR by D-RAD, we achieved a small magnetic field of −100 Oe for readout. In recording on a D-RAD MO disk with land/groove recording, a C/N of more than 45 dB for a mark length of 0.27 μm and a cross-talk level of less than −40 dB at a track pitch of 0.7 μm were achieved. In addition, a combination of light intensity modulation direct overwrite (LIMDOW) with D-RAD was achieved by adding on MSR switching layer to D-RAD.
Single crystals of an interstitially modified nitrogen compound, Nd2Fe17N3, were successfully synthesized for the first time by means of the high-pressure N2 gas nitrogenation technique. High-field magnetization curves along the rhombohedral principal axes for the Nd2Fe17 and Nd2Fe17N3 single crystals at 4.2 K indicated strong anisotropic behaviors, which were analyzed on the basis of a single-ion Hamiltonian including the Zeeman energy, exchange energy, and crystalline electric field (CEF) effect. The results indicate that the second-order CEF coefficient A20 reaches up to −1.5 × 103 K/a20 at 4.2K upon nitrogenation, which is about three times as large as that for Nd2Fe17.
The effects of additives (M = Al, Ti, Ga, Zr, Sn) on the magnetic properties of Sm2Fe15CoMn0.9M0.1Nx coarse particles were systematically examined, including the nitrogenation conditions and nitrogen content It was found that both the coercivity and residual magnetization of Sm−Fe−N particles were enhanced by enrichment of the nitrogen content in combination with addition of Co−Mn−Ti. The magnetic properties of Sm2Fe15CoMn0.9Ti0.1N5.3 coarse particles ∼50μm in diameter were as follows: σs=117emu/g, σr=109emu/g, iHc=8.6kOe, and (BH)max= 18MGOe.
The magnetic properties and microstructure of Sm2 (Fe0.95Mn0.05)17Nx and Sm2 (Fe0.84Co0.11Mn0.05)17Nx powders were investigated. It was found by high-field magnetization measurement in steady fields of up to 150 kOe that the intrinsic saturation magnetizations of Sm2(Fe0.95Mn0.05)17Nx and Sm2 (Fe0.84Co0.11Mn0.05)17Nxx=3.3-5.5 were 130-160 emu/g. The theoretical (BH)max value for Sm2 (Fe0.95Mn0.05)17N3.3 is calculated to be about 60 MGOe (ρ=7.70 g/cm3, Ms=15.5kG). The anisotropy fields of Sm2(Fe0.95Mn0.05)17Nx and Sm2(Fe0.84Co0.11Mn0.05)17Nx powders were estimated to be 140-170 kOe by extrapolation of the magnetization curves. From TEM observations, it was found that the Sm2(Fe0.95Mn0.05)17N5.5 powder had a cell structure consisting of the crystals about 10 nm in diameter. It is concluded that the magnetic reversal of Sm2(Fe0.95Mn0.05)17N5.5 powder is pinning-controlled, judging from the microstructure and the relationship between the coercivity and the maximum applied field.
Sm2Fe17N3 powders used in permanent magnets are composed of three types of particle: (1) single-domain particles (SDPs), (2) multi-domain particles (MDPs) in which the domain walls move under a relation of Happl. = NM, where N is a demagnetizing factor, M is the magnetization in a particle and Happl. is an applied magnetic field, and (3) particles that behave as MDPs in a demagnetized state, but can be magnetized to become SDPs under a certain magnetic field and behave as SDPs unless renucleation occurs. The authors studied the magnetization and nucleation behavior of the last type of particles, which they call saturable multi-domain particles (SMDPs). In this report, the relation between magnetization and nucleation fields in SMDPs is measured for isolated and isotropically distributed Sm2Fe17N3 particles.
We studied the magnetic properties of Nd-Dy-Fe-Co-B-Zr-Ga magnet powders produced by the hydrogenation-decomposition-desorption-recombination (HDDR) process, using a hydrogen pressure of 0.1 MPa. Magnet powders with iHC higher than 1200 kA/m were obtained from alloys of Nd11.3Dy1.3Fe80-yCoyB7.0Zr0.1Ga0.3, y≤11.6 at%. It was found that annealing in an Ar atmosphere added after the HD treatment in the HDDR process improved the magnetic anisotropy of the magnet powders. Typical magnetic properties of the magnet powders obtained by this process are as follows: Br=1.27T, iHc=1280 kA/m, (BH)max=283 kJ/m3, and β=-0.44%/°C.
The granulation of Nd-Fe-B powder was investigated by the spray-drying method, using poly (vinyl alcohol) as a binder to give it good flowability. The amount of oxygen and carbon in sintered magnets can be controlled below the upper limit by cooling the slurry and debinding green compacts in a hydrogen atmosphere. As the granulated Nd-Fe-B powder has good flowability, thin green compacts can be easily produced from it, and the sintered bodies are highly accurate in size. Micro-ring magnets with a thickness of 0.6 mm and thin-plate magnets with a thickness of 0.2 mm were successfully synthesized by spray-dried Nd-Fe-B powder without any serious damage to the surfaces by oxidation, which harms coercivity and the squareness of demagnetization curve.
Exchange-spring-bonded magnets of Nd-Fe-Co-Cu-Nb-B system alloys were prepared by using melt-spun ribbons heated at 650°C for 10 min. Bonded magnets of Nd-Fe-Co-Cu-Nb-B system alloys were examined to determine their magnetic properties, low-temperature properties, and irreversible flux losses. The irreversible flux loss of these bonded magnets at 100°C was less than 5%. Spin reorientation was observed below —120°C. The optimum preparation conditions and some properties are as follows: composition, Nd5Fe71Co5Cu0.5Nb1B17.5; wheel velocity, 20 m/s; annealing condition, 650°C × 10 min in Ar atmosphere; magnetic properties, Jr=0.776 T, HcJ = 320.4 kA/m, HcB = 253.0 kA/m, (BH)max = 57.82 kJ/m3, Hk/HcJ × 100 = 20.65%, D=6.17Mg/m3.
Exchange-spring magnets of NdxFe86-xCo8V1B5 and NdxFe85-xCo8V1B6 (x=6−9) alloy ribbons were prepared by the single-roller rapid quenching method. The effects of the composition and annealing treatment on the magnetic properties were investigated. The values of (BH)max and HcJ were found to increase with the Nd content, while, the value of Br decreased slightly. The optimum preparation conditions and some properties were as follows: composition, Nd9Fe76Co8V1B6; roller speed, 20 m/s; annealing condition, 675°C × 0 min; magnetic properties: (BH)max = 165.4 kJ/m3, HcJ = 455.4 kA/m, HcB = 423.3 kA/m, Br= 1.11 T, α (Br)= −0.067 (%/°C), β (HcJ) = −0.33 (%/°C), Hk/HcJ × 100 = 44.7%, Tc = 448°C. From TEM observation, the particle size of this ribbon was determined to be 20 to 30 nm.
The magnetic properties of nanocrystalline bulk Fe100-x-yCoxNb2(Nd, Pr)yB5 (x=0-20, y=5 and 7) alloys produced by consolidating and crystallizing amorphous powders under uniaxial pressure were investigated. The bulk alloy produced by consolidating amorphous Fe66Co20Nb2-Pr7B5 powder at a temperature (Ts) of 873 K under a uniaxial pressure (Ps) of 636 MPa had a density of 7.56 × 103 kg/m3 and formed a nanocrystalline composite structure of bcc-(Fe, Co), (Fe, Co)3B, and Pr2(Fe, Co)14B phases in the as-consolidated and annealed (973 K) states. Nanocrystalline bulk Fe100-xCoxNb2(Nd, Pr)7B5 (x=0-20) alloys showed remanence enhancement, associated with an exchange-spring magnet, and anisotropic magnetic properties presumably due to the alignment of (Nd, Pr)2(Fe, Co)14B phase caused by crystallization under uniaxial pressure. The maximum energy product ( (BH)max) measured parallel to the press direction was found to be 94 kJ/m3 for Fe66Co20Nb2Pr7B5.
New Fe-based amorphous alloys exhibiting the glass transition and supercooled liquid region before crystallization were searched for in the composition range of Fe63Co7Nd10-xZrxB20 (x=0 to 6 at%). Amorphous alloys containing 4 to 6 at%Zr were found to exhibit the glass transition followed by a supercooled liquid region. The crystallization of the 4 at%Zr and 6 at%Zr alloys occurred in three stages. In the crystallized state, the alloys exhibited hard magnetic properties, namely, Js of 1.15 to 1.18 T, Jr of 0.75 to 0.76 T, and Nd2Fe14B phases for the 4 at%Zr alloy subjected to optimum annealing were about 50 nm and 30 nm, respectively, and the exchange magnetic coupling interaction between the α-Fe and Nd2Fe14B phases is thought to make possible the appearance of the hard magnetic properties.
The quenching conditions for the formation of a nanocomposite microstructure in rapidly-solidified Nd4Fe77.5B18.5 alloys were investigated in order to obtain a hard magnetic material consisting of Fe3B and Nd2Fe14B in the as-quenched state by means of the Cu single-roll melt-spinning technique. It was found for the first time that as-spun Fe3B/Nd2Fe14B hard magnets can be obtained directly from a molten alloy when the melt-spinning process is carried out under a reduced chamber pressure of 1.3 kPa Ar on a Cu-roll surface moving at a velocity of 5 m/s. The as-spun Nd4Fe77.5B18.5 hard magnet has a thickness of 190 μm and magnetic properties of Jr = 1.25 T, (BH)max = 118.1 kJ/m3, and HcJ = 276 kA/m at room temperature. The Fe3B/Nd2Fe14B nanocomposite hard magnets obtained by this technique may be used to produce thin-plate permanent magnets.
A spin-polarized scanning electron microscope (SP-SEM) with a retarding-type Mott analyzer was developed. For SP-SEM applications, we improved the figure of merit of the polarimeter, which had been developed in our laboratory, and employed a newly designed secondary electron collector. To avoid the magnetic stray field generated by the magnetic objective lens, a magnetic shield whose shape was designed by means of the finite element method was attached to the lens. Using the SP-SEM system, we observed spin-dependent SEM images of the domain structure of a single Fe crystal (001) surface, and typically observed spin polarization of secondary electrons of about ±14%.
The crystal structure of copper iron oxide (CuFe2O4:Cu-ferrite) is transformed from cubic spinel to tetragonal symmetry by the Jahn-Teller (J-T) distortion. The degree of J-T distortion σ is theoretically given by the function σ=σ0 tanh (|A|σ/RBT), where σ0 is the degree of the distortion at 0 K, A is the energy term involved in the distortion, RB is Boltzmann's constant, and T is the absolute temperature. The films were prepared by vacuum evaporation and solid reaction, and their crystal structure, magnetic coercive force, and initial magnetization energy were investigated. The temperature dependence of the shift of the Bragg angle Δ2θ for XRD, the coercive force Hc, and the initial magnetization energy Ei were well fitted to the function C tanh (α/T−β), where C, α, and β are constants determined by experiment. Consequently, the interaction between the distortion and magnetic properties of Cu-ferrite films was considered to be caused by J-T distortion, and experimental results agreed with the theorem of J-T distortion.
Highly-oriented (Er1-xTbx)2Fe14B ribbons with 0 ≤ x ≤ 0.45 were fabricated by a rapid-quenching method. The c-axis of the tetragonal cell was aligned perpendicular to the ribbon surface. Magnetostriction measurements were made by using the capacitance method, and showed that the sum of the longitudinal and transverse magnetostriction λ// + λ⊥. within the ribbon plane took a maximum at successive spin-reorientation temperatures. A model calculation of the volume change ΔV/V in the vicinity of the spin-reorientation temperatures was made by assuming that only the lowest crystal field term A02 affects the volume change. This calculation showed that ΔV/V exhibits a sharp peak at spin-reorientation temperatures, which is in accordance with the experimental peaks of λ// + λ⊥.
The magnetic and electrical properties of two-dimensional epitaxial a-axis Lan-nxCa1+nxMnnO3n+1 (n=2, 3; x=0.3) films and three-dimensional La1-xCaxMnO3 (x=0.3) film were studied. Various systematic changes in the properties were observed as n (the number of MnO2 layers) was reduced. These included a decrease in the resistivity peak temperature (Tρmax), and enhancement of the magnetoresistance near Tρmax and the characteristic low-temperature magnetoresistance whose field dependence has a hysteresis curve. It is concluded that the changes result from a decrease of the transfer (tcij) along the c-axis of the crystal and the effect of spin fluctuation between MnO2 layers.
Using a local-doping technique with 57Fe MÖssbauer probes, a depth-dependent micromagnetic structure in [Co (20 Å)/Au (20Å)]N-1/Co (20Å) multilayer films with perpendicular anisotropy was investigated. As a result, (1) a smooth spin reorientation from in-plane to out-of-plane was found as a function of the laminating number N ac-companied by a change in the micromagnetic structure, and (2) the average spin orientation and dipole field in Co layers of [Co/Au]30/Co were found to be strongly depth-dependent, that is, they were closer to the film normal at the middle part of the multilayer than near the surface. The latter findings were attributed to the presence of a flux closure pattern in the perpendicular plane throughout the multilayer structure. The paper also discusses a spin rearrangement phase transition of the magnetic multidomain structure in a [ferromagnetic/nonmagnetic]N multilayer film with moderate perpendicular anisotropy as a parameter of N.
After establishing the usefulness of the ion implantation technique for synthesizing diluted magnetic semiconductors (DMSs) in the case of Zn1-xCoxTe, we have used the technique to obtain Ni-based DMSs, which have not been reported before. Ni ions were implanted into an epitaxially grown ZnTe film. The magnetic circular dichroism (MCD) spectra of the implanted films clearly showed that the Ni ions replaced Zn ions and induced a Zeeman split of the optical transitions. Analyses of the MCD spectra and the Zeeman splitting showed that the p-d exchange interaction in Zn1-xNixTe was antiferromagnetic, and that its magnitude could be the largest ever reported for DMSs.
To obtain amorphous FeB-plated films with soft magnetization, the effect of a combined complex agent of potassium sodium tartrate (KNaC4H4O6 · 4H2O) and ammonium sulfate ( (NH4)2SO4) on the film properties was investigated. Soft magnetic films with coercivities of less than 4 Oe were obtained by using a bath composition of KNaC4H4O6 · 4H2O = 600mmol/L and (NH4)2SO4 = 80mmol/L. These soft films also exhibited large magnetostriction of 26 × 10-6, suggesting that the use of the combined complex agent is very effective for obtaining FeB amorphous films that have soft magnetic properties and large magnetostriction simultaneously. Change in composition of films along their thicknesses is considered to be responsible for the magnetic softening of FeB-plated films.
Improvements in the magnetic and magnetostrictive properties of amorphous FeB sputtered films were achieved by doping them with rare earth elements (RE = Pr and Tb) were examined in detail for the composition system Fe100-x-yBxREy (x = 15-40 at%, y = 0-3.5 at%). It was found that magnetic softening is promoted by adding a small amount of RE (y = 1 at% for Pr, y = 1.5 at% for Tb), while ensuring that film maintains a relatively high magnetostriction constant. These properties remain almost completely insensitive to thermal annealing at temperatures up to 350°C, suggesting that RE elements with large ion radii act as impurity elements, causally stabilization of the amorphous structure and an increase in the electrical resistivity. The linear change of λ vs. H without any hysteresis loop and the high magnetostrictive sensitivity dλ/dH are very favorable for sensor and/or actuator applications.
Fe-N thin films were prepared on crystallized glass and MgO (100) single-crystal substrate at room temperature by RF sputtering with an RF bias ranging from 0 W to 75 W at a deposition rate of between 0.5Å/s and 0.8Å/s. The X-ray diffraction peaks of γ'-Fe4N decreased with increasing RF bias. In Fe-N thin films prepared on crystallized glass, an α''-Fe16N2 phase and α'-martensite phase were not formed, and the saturation magnetization Ms of the films did not exceed that of bulk α-Fe. In the Fe-N thin films prepared on MgO (100) single-crystal substrate with RF biases of 20 W and 25 W, α'-martensite phase were formed. The Ms for an RF bias of 20 W was 227 emu/g, which was 4.1% higher than that of bulk α-Fe.