The MR ratio of a cross geometrical ferromagnetic tunnel junction with a spin-valve-like structure of Ni-Fe/Co/Al-O/Co/Ni-Fe/Fe-Mn/Ni-Fe is dependent upon annealing temperature. In this study we investigate the cause of this dependance using I-V measurements, X-ray photoelectron spectroscopy (XPS), and X-ray reflectivity. The behavior of the MR ratio as a function of annealing temperature agrees well with the behavior of barrier height estimated from I-V curves. Therefore we consider that the dependence of MR ratio on annealing temperature is caused by the dependence of barrier height on annealing temperature. From XPS and X-ray reflectivity, we find that the dependence of barrier height on annealing temperature is caused by the change of oxidization of the Al-O layer.
The tunnel conductance through a disordered spacer is studied in the linear response theory at zero temperature. It is shown that the conductance is proportional to the product of surface densities of states of metals separated by the spacer when the disorder is strong.
Junctions with Al2O3 and AIN barriers were fabricated through contact shadow masks (0.25mm2-size) and by a self-aligned lithography process (9×2μm2-size). The Al2O3 barrier was formed by plasma oxidation. The AlN barrier was prepared by dc reactive magnetron sputtering. Room temperature tunneling magnetoresistance (TMR) is 1.6% for the AIN junctions and up to 24% for the Al2O3 junctions. The TMR for all junctions decreases with increase of applied bias voltage and drops to half its initial value at a bias voltage between 116 mV and 437 mV. The weakest bias voltage dependence occurs for junctions with higher barrier heights, and thinner barrier thickness. Annealing at 100-200 °C leads to a 20% increase of TMR and a 40% decrease of junction resistance for the 9×2μm2 junctions, leading to a maximum TMR of 27%. Both TMR and junction resistance were increased for the AlN junctions due to annealing.
We investingate the tunnel magneto-resistance ratio (TMR) of the model that the electron state in the ferromagnetic electrodes is written by the free electron in the exchange magnetic field, and that in the insulating film is written by the tight-binding model. The bias voltage and temperature dependences of TMR for various barrier heights are calculated by employing the Keldysh formalism. The TMR at 0 K decreases in proportion to the bias with decreasing the bias. The TMR at zero bias also decreases with increasing the temperature. The proportion of the decrease is smaller than that with increasing the bias.
Transport phenomena through a tunnel junction in the presence of impurities in the insulating layer are investigated in the finite temperature and finite bias voltage. We have found that the effect of the temperature on the tunnel conductance in the non-linear current-voltage (I-V) characteristics is smaller than that in the linear- response case.
Inelastic-Electron-Tunneling-Spectroscopy (IETS) has been applied to investigate the electron states of the interface of Al/Al2O3/Co(dCo)/Al tunneling junctions. A zero-bias anomaly was observed in the conductance curve of the junction with dCo of 2 Å and decreased with increasing dCo. The IET spectra of these junctions showed a strong negative peak at 4 mV, corresponding to the zero- bias anomaly, while the another broad peak was observed for the junctions with dCo ≥10Å. The peak was different in the position from that assigned to the Al-O LO phonon mode observed for Al/Al2O3/Al junction. From the magnetization measurement, it is confirmed that the ferromagnetic layer was formed for the junctions with dCo ≥10 Å These results were discussed with the paramagnetic impurity and magnon assisted tunneling process.
Tunnel magnetoresistance (TMR) has been investigated in single (Ni-Fe/Al2O3/Co) and double (Ni-Fe/Al2O3/Co/ Al2O3/Co) tunnel junctions. The Al2O3 layer was formed by a direct sputtering method with an Al2O3 target. Metal masks were used to form a cross pattern geometry. In the single junctions the dependence of the tunnel resistance and the TMR ratio on the Al2O3 thickness was investigated. The tunnel resistance increased exponentially with increasing the Al2O3 thickness. A maximum TMR ratio was 4-5 %. In the double junctions the dependence of the tunnel resistance and the TMR ratio on the thickness of central Co layer was investigated. The tunnel resistance decreased with increasing the Co thickness. The maximum TMR ratio was 2%, which was smaller than the value of the single junctions.
We prepared ferromagnetic tunneling junctions by ion beam sputtering technique and measured magnetoresistance and I-V characteristics. Insulating barriers with the barrier height of 0.1-0.6eV were formed by exposing a thin Al metal layer to Ar+O2 beam from the assist ion source. The magnetoresistance of 4% was observed in Fe/Al-O/NiFe/FeMn at 77K. Inserting a thin Co layer between the insulating barrier and the NiFe layer improved the magnetoresistance up to 18%.
We have investigated the Hall effect and thermoelectric power (TEP) in Co-Al-O and Fe-Al-O granular films. The extraordinary Hall resistivity was found to decrease on approaching the tunneling regime. Even on tunneling type samples, we observed finite thermoelectric voltages, which exhibit large field dependence correlated with the giant magnetoresistance.
The relationship between the tunnel-type magnetoresistance(TMR) and the structure of metal-nonmetal granular system (Fe-Co)-Al-O films has been examined. Films were prepared by a tandem deposition method with rotating a substrate holder. The average diameter of metallic granules is found to decrease with an increase in the rotating speed of substrate holder without any change of film composition. And the MR ratio increases with a decrease of the diameter of metallic granules. The influence of the granule diameter on the MR ratio is discussed by so-called coulomb blockade effect. Furthermore, we studied the effect of a substrate temperature(Tsub.) on the MR and the structure of films. The MR ratio and electrical resistivity of the films increase with an increase of Tsub.. The magnetization measurements suggests that these increases are related with the decrease of the amount of magnetic impurities in the Al-oxide intergranule. The phase separation between the metallic granule and the oxide intergranule may take place in the film prepared on the higher Tsub..
A Co-Al-O granular thin film was prepared on glass substrates by reactive sputtering method with mixed gas of Ar+O2. The sample was annealed at 300°C for various annealing time to change the microstructure. The temperature dependence of electrical resistivity (ρ) shows the relationship of logp versus T-1/2 for the sample annealed for 1 and 6 hours. However, the sample annealed for 38 hours shows the relationship of logρ versus T-1/4, which represents a significant change in the transport mechanism. Although the transport mechanism was changed, GMR appeared for 38hours-annealed sample. The magnitude of GMR decreases with increasing annealing time. Particularly, GMR reveals a noticeable decrease at low temperatures on annealing.
We have observed scanning tunneling microscopy (STM) topographic images for structural characterization and measured current-voltage (I-V) spectra (scanning tunneling spectroscopy: STS) for the investigation of local transport properties of Co-Al-O granular thin films exhibiting tunnel-type giant magnetoresistance (GMR). STM topographic images indicated round-shaped bright regions and dark channels, which are associated with Co granules and Al-oxide, respectively. From the I-V characteristics the electronic charging effect, i. e., the effect of Coulomb blockade, was confirmed. In addition, the tunneling current varied stepwise as a function of the voltage, suggesting the appearance of a Coulomb staircase.
Fe/Si films were prepared by evaporating Fe and Si alternately at various substrate temperatures Ts between 100 and 623K. The nominal thicknesses of Fe and Si were fixed at 3.4Å and 6Å, respectively. The films prepared at Ts higher than 200∼300K showed a superparamagnetic behavior, and also an isotropic magnetoresistance (MR) of 0.02%. On the other hand, the films at lower Ts showed an anisotropic MR similar to that observed in most ferromagnets. These results suggest that the film structure is changed from a granular like one at low Ts to a partially a continuous one at high Ts. These structure changes may come from an interdiffusion and/or a reaction between Fe and Si in the films.
Current status of III-V based ferromagnetic semiconductors, especially (Ga, Mn)As, a GaAs based diluted magnetic semiconductor, is reviewed. Low solubility of magnetic elements was overcome by low temperature nonequilibrium molecular beam epitaxial growth to realize successfully (Ga, Mn)As as well as (In, Mn)As. Magnetization measurements showed that GaAs based (Ga, Mn) As is ferromagnetic with Curie temperature TC as high as 110 K. Magnetotransport measurements of (Ga, Mn) As epitaxial films revealed that the p-d exchange N0β is 3 eV. This strong interaction was shown to be large enough to explain the high TC by the RKKY interaction. Multilayer heterosturctures including superlattices and resonant tunneling diodes (RTD's) were also successfully fabricated. The magnetic coupling between two ferromagnetic (Ga, Mn)As films separated by a nonmagnetic GaAs (or AlGaAs) layer was found to be a function of thickness and composition of the intermediary layer, indicating the critical role of the holes on the magnetic coupling. This observation of magnetic coupling in all semiconductor ferromagnetic/nonmagnetic layered structures, together with the possibility of spin dependent tunneling in RTD's, showed the potential of the present material system for exploring new physics and for developing new functionality toward future electronics.
(Alx Ga1-x)l-yMnyAs films were grown by molecular-beam epitaxy at various Al compositions. The Al+Ga flux andMn flux were kept constant. In the case of the growth at the Al composition up to 0.5, homogeneous (AlxGa1-x)l-yMnyAs alloy was grown with zincblende structure, whereas inhomogeneous films with both zincblende (AlxGal-x)1-yMnyAs and hexagonal MnAs became amorphous thereafter. The Mn composition of the (AlxGal-x)l-yMnyAs films increased from 0.03 to 0.06 as the Al composition increased from 0 to 0.5. These results indicate that the incorporation rate of Mn atoms into (AlxGa1-x)l-yMnyAs films increases with the increase of the Al composition. The linear relationship was observed between the lattice constant and the Mn composition of the (AlxGa1-x)l-yMnyAs films, independent of the Al composition.
Growth condition dependence of electronic, magnetic and optical characteristics of magnetic semiconductor (GaMn)As is studied. With decreasing the As4 overpressure during the growth of (GaMn)As, the conduction behavior became more metallic, the ferromagnetic transition temperature became higher, and the magneto-optical response got strong. Besides, photoluminescence was obtained from the (GaMn)As samples grown under low As4 overpressure.
All-semiconductor ferromagnet/nonmagnet/ferromagnet trilayer structures using (Ga, Mn)As as a ferromagnetic layer and GaAs a nonmagnetic layer were prepared and their magnetotransport properties were investigated. The results show that the interaction between the two (Ga, Mn)As layers decreases as the GaAs thickness increases. This shows that the carriers present in the nonmagnetic layer mediate the coupling between the two ferromagnetic layers in the present all-semiconductor system.
The lattice parameter, transport properties, and magnetoresistance effect of perovskite manganite La0.7Ca0.3MnO3thin films deposited on several substrates (SrTiO3(001), LaSrGaO4(001), YAlO3(001), LaA1O3 (001)) have been investigated in the range of themismatchof -4∼1% between the film and the substrates. We have found that metal-insulator transition temperature (Tcρ)depend on the out-of-plane lattice parameter (c). Magnetoresistance effect increases linearly with decreasing Tcρ. These results are understood in terms of the latticeeffect induced by the strain.
Polycrystalline perovskite with composition La0.67Ca0.33Mn0.99Fe0.01O3 has been produced by a metal- salt routed sol-gel processing method. Colossal magnetoresistance of La0.67Ca0.33Mn0.99Fe0.01O3 has been studied with x-ray diffraction, Rutherford back-scattering spectroscopy, Möossbauer spectroscopy and vibrating sample magnetometer. Crystalline La0.67Ca0.33Mn0.99Fe0.01O3 was perovskite cubic structure with a lattice parameter a0=3.868 Å. Mössbauer spectra of La0.67Ca0.33Mn0.99Fe0.01O3 have been at various temperature ranging from 4.2 K to room temperature. Analysis of 57Fe Mössbauer data in terms of the local configurations of Mn atoms has permitted the influence of the magnetic hyperfine interactions to be monitored. The values of the isomer shifts show that all iron ions are in the Fe3+ state. For magnetic fields > 8 kOe and T < 100 K the magnetic moment is saturated at the value is 85 emu/g. The Curie temperature, Tc, is determined to be 270 K. The doping of 57Fe reduces Curie temperature and saturation magnetization. The temperature dependence of the resistance for La0.67Ca0.33Mn0.99Fe0.01O3 under zero and 10kOe applied field is shown that a semiconductor-metal transition, TSC-M, occurs at 250 K. The relative magnetoresistance, MR, defined as : [R(0) -R(H)]/ R(H), is about 33 %.
Using single phased Ce2Fe17 and Lu2Fe17 with the rhombohedral Th2Zn17-type and Th2Ni17-type structure, respectively, we performed measurements of magnetization and resistivity under various magnetic field up to 5.5T. Ce2Fe17 exhibits a simple helical spin structure with a wave vecter of τ= 0.0372 Å-1 parallel to the c-axis in the temperature range of TC=125K < T<TN = 210 K. For T<TC, it shows a modified helix of τ= 0.0435 Å-1 parallel to the c-axis with a superstructured magnetic cell, in which the magnetic c-parameter is twice as large as the chemical unit cell. Only below TC, a giant magnetoresistance is induced by a metamagnetic transition from the helix to ferromagnetic phase in the field of H < 2T. The value of Δρ/ρ(= (ρAF-ρF )/ρAF) reaches 0.85 at 4.2 K. Such GMR may be atributed to the suppression of a super-zone gap induced by a formation of the superstructured magnetic cell below TC. On the other hand, GMR could not be observed in Lu2Fe17.
Break-junction measurements on Ce2Fe17 have been carried out for the first time. The differential conductance exhibits the gap feature associated with the antiferromagnetic state below TN1 = 125 K. The gap magnitude of 2Δ = 13-16 meV at 4.2 K corresponds to 1.2 - 1.5 kBTN1, which is considerably smaller than the mean-field prediction. We also observed distinct conductance structures at higher bias voltages. Their possible origins are briefly discussed.
The microwave measurement of GMR effect in the CPP geometry is realized and investigated. It is shown that the magnetic field dependence of microwave absorption undoubtedly correlate with the CIP DC magnetoresistance of superlattices.
Effects of pressure on the giant magnetoresistance (GMR) at various temperatures are studied for [Co(10.8Å)/Cu(tCuÅ)]15 magnetic multilayers (MMLs) with tCu near the first peak (tCu≈10)of MR ratio. A significant difference is found that the pressure effect on the magnitude of MR ratio of Co/Cu for tCu=9.8 decreases with increasing pressure, while that for tCu= 11.7 increases. This enhancement of GMR in Co/Cu with tCu=11.7 caused by applying pressure, at 5 K, 77 K and room temperature, is the first observation in Co/Cu MMLs.
The effect of the compositional modulation and the structure near the layer boundary between ferromagnetic and nonmagnetic metals, on magnetoresistance (MR) in the Co/Ca and Co/Ag multilayers produced by pulse electrodeposition method has been investigated. It was possible to control the film thickness in the range of 4.5-39 Å by electrodeposition. From the experiments on the films with composition modulation near the layer boundary between ferromagnetic Co-rich layer and nonmagnetic Cu layer, it is observed that the MR ratio strongly depends on the thickness of the ferromagnetic layer rather than the change of the composition near the interface between magnetic and nonmagnetic layers.
Giant magnetoresistance (GMR) effect in Co(5nm)/Cu(3.5nm)/Co(5nm)sandwiches with different thickness Ni buffer layers was investigated. It was found that the usage of a Ni buffer layer could enhance the MR ratio and sensitivity of the sandwich significantly. MR ratios from 3.5% to 5.6% were obtained and MR curves were found to saturate in a field about 30 Oe. Furthermore, field sensitivities larger than 1%/Oe were observed in these sandwiches. X-ray diffraction analysis showed that (111) texture was formed in Ni buffered sandwiches. Atomic Force Microscope images also indicated that interface roughness of the sandwiches could be reduced by the Ni buffer layer. It was considered that Ni buffer layer played an important role in the improvement of magnetic characteristic, MR ratio and sensitivity of the sandwiches.
The GMR effect of the [(Ni83Fe17=Py)/Cu]x100 multilayers (Mls) obtained by d. c. face-to-face sputtering technique deposited onto Si wafers were studied at room temperature (R. T.) and at 4.2 K. The GMR(dCu) oscillatory behaviour as well as the width of the first and the second AF coupling ranges have been found to be strongly affected not only by the presence of the superparamagnetic entities located at the Py/Cu interfaces but mainly by the existence of the magnetic bridges between Py sublayers. Zero-field-cooled and field-cooled magnetisation measurements confirmed the existence of the paramagnetic/superparamagnetic areas (at R. T.) for Py thicknesses up to 2.5 nm. The effectiveness of the magnetic bridges between Py sublayers has been found to be temperature dependent, leading to the temperature dependence of the remnant to saturation magnetisation ratio.
The GMR of 1(2,3)-dimensional magnetic superlattice and multilayer from RKKY coupling is derived by using the green's function method and the free electron model. Based on the contributions to GMR from RKKY coupling, we get the thickness and temperature dependencies of GMR. Numerical calculations are finished by using a simple model. Comparing with the theoretical oscillatory GMR-d curves in different dimensions and the experimental ones in different multilayers, we discuss the dimension and thickness dependencies of GMR curves.
We report large magnetoresitance (MR) ratios in dual spin-valves of α-Fe2O3/Co/Cu/Co/Cu/Co/α-Fe2O3 and α-Fe2O3/Co/Cu/Co/Cu/Co/IrMn. The MR ratios of the spin-valves are 27.8% for the former and 20.9% for the latter. The larger GMR in the α-Fe2O3 top spin-valve implies the evidence of the specular reflections at the Co/α-Fe2O3 interfaces.
Spin valve structure as NiO/Co/Cu/Co/NiFe on glass substrate was prepared by rf magnetron sputtering. We systematically studied the effects of the deposit conditions such as biased pressure. sputtering power. gas pressure. deposit magnetic field and temperature of substrate on magnetic and magnetoresistance properties of this system. The influence of thickness of space layer Cu and inserted thinner Co layer in free ferromagnetic layer on MR is also discussed
Co20Cu80 binary alloy is produced by mechanical alloying. The magnetoresistance (MR) and magnetic properties in temperature range from 5K to 300K, have been investigated for the as-milled and annealed alloys. The MR for the as-milled sample measured at the temperatures below 120K is not proportional to the square of magnetization M2. However, the MR for the annealed sample changes almost following M2 even below this temperature. With decreasing temperature, the MR ratio for the as-milled sample slightly increases and becomes a constant value of about 3% below 180K, and for the annealed sample monotonously increases and shows about 14% at 5K.
We study the scattering of an electron by a ferromagnetic domain wall of the quantum Heisenberg-Ising model (XXZ model) with certain boundary conditions. The spin of the electron interacts with the spins of the XXZ model by the Hund coupling. Using the exact domain wall ground states of the XXZ model, we analytically obtain the exact effective Schrödinger equation for conduction electrons. This equation coincides with a conventional phenomenological Schrödinger equation which was derived in a classical treatment of spins of a domain wall. By solving the Schrödinger equation numerically, we have calculated the transmission coefficient which is a function of the Hund coupling and of the anisotropy of the XXZ model. It turns out that the transmission coefficient is vanishing in the low energy limit for the electron.
The annealing effect on the magnetoimpedance of nanocrystalline Fe84Zr7B8Cul alloy has been investigated in conjunction with the changes of magnetic properties such as permeability, magnetic anisotropy, etc. by thermal treatment. The magnetoimpedance ratio coincides with the softness of magnetic properties of thermally treated samples. The field - annealing doesn't contribute to improve the magnetoimpedance effect in the nanocrystalline alloy.
We report results on the magneto-impedance effect in Fe73.5Cu1Nb3Si13.5B9 nanocrystalline glass-covered wires, Co68.15Fe4.35Si12.5B15 amorphous wires, and in such wires after glass removal. The results are compared with those obtained for cold drawn and then tension annealed Co68.15Fe4.35Si12.5B15 amorphous wires. The magneto-impedance response of nanocrystalline wires after glass removal is larger than that of CoFeSiB amorphous wires after glass removal, being almost equal to that of cold drawn CoFeSiB amorphous wires. The results are explained in terms of specific domain structures and magnetic properties of the discussed wires, and they reveal the importance of good soft magnetic properties in a large magneto-impedance effect.
The role of alloyed atomic layers was studied in Fe/Cu/X(c)Cu(1-c)/Cu/Fe(001) systems, where X=Ag, Cr, Fe. The experimental results and theoretical calculations show that the strength of the coupling mostly depends on the magnetic state of the foreign atoms. For foreign atoms with no long range ferromagnetic order the strength of the coupling is mostly affected by mismatch in the valence bands. Foreign atoms that are isoelectronic with the spacer atoms modify the coupling only due to lattice relaxations. The role of heterogeneous interfaces in Fe/Cr systems was studied using Fe-whisker/Cr/Cu, Ag, Mn/Fe(001) structures which were prepared by layer by layer epitaxial growth. The results using the samples with Cr/Cu/Fe and Cr/Ag/Fe interfaces indicate that the spin dependent reflectivities play a significant role in the exchange coupling through Cr(001). The Mn layers in Cr/Mn/Fe(001) have either ferromagnetic or compensated antiferromagnetic order, and can result in a significant enhancement of the interlayer exchange coupling.
Fe/Tb multilayer films show a ferrimagnetic behaviour. The magnetic properties belonging to these systems, like the magnetic anisotropy or the saturation magnetization, can be varied by an thickness modulation of the single layers. The ferrimagnetism has the origin in the antiparallel coupling of two magnetic sublattices. The first sublattice is generated by the ferromagnetic Fe-layer and the second one originates from polarized paramagnetic Tb-layers. This ferromagnetic polarization of the Tb-layer is caused by an indirect long range exchange coupling between the Fe- and Tb-layers. For a detailed study of the named interaction the Fe- and the Tb layers were separated by a non magnetic metal interlayer (like Pt, Au, Cu or Ta) was observed. The sign of the coupling depends on the interlayer metal. In the case of Pt, Ta and Cu interlayers an antiparallel coupling of the magnetic moments of the Fe and Tb layers was observed. In the case of Au interlayers the coupling provides parallel orientation of the magnetic moments of the Fe layers and the induced moment of the Tb layers. In both cases of coupling the net magnetic moment of the multilayer system oscillates with increasing thickness of the non magnetic interlayer. The length of the oscillation period depends on the material of thenon magnetic metal interlayers.
A technique is presented by which it is possible to obtain information on the exchange coupling between Fe layers across Au interlayers, in fine layered structures of Fe and Au. By understanding the layered structure as a diluted magnetic alloy one can determine its effective exchange constant by measuring the frequencies of the spin waves. These are the standing spin wave modes of this material. The surface localized Damon-Eshbach mode does not contribute to information about exchange but is used for the determination of other parameters, for example the g-factor. The relation between the thus determined effective exchange and the interlayer exchange will be discussed.
We report on the effect of exchange interactions between antiferromagnetic (AF) NiCoO and ferromagnetic (FM) Permalloy (Py) layers in NiCoO/Py/MgO trilayers. The AF layer not only creates exchange bias in the FM layer but also enhances its coercivity substantially, by two orders of magnitude at low temperature. Unidirectional anisotropy was found to exist even in samples with just 10 Å of AF layer thickness. Studies on the dependence of coercivity and exchange bias on the angle between the applied field and the exchange bias direction were also performed and the results will be reported.
Exchange anisotropy between NiO antiferromagnetic layer and NiFe ferromagnetic layer has been investigated in Ta(5 nm)/NiFe(10 nm)/NiO(60 nm)/Si(100) formed by magnetron sputtering. NiO was sputtered from nickel oxide using R. F. power and NiFe, Ta were deposited using D. C. power under Ar atmosphere. Among the variables of sputtering conditions, our experimental data showed that the dominant factor for determining the exchange anisotropy properties was the Ar pressure during NiO deposition. The better exchange anisotropy properties were found when the NiO film was deposited at low Ar pressure probably due to the abrupt and flatten interface and the epitaxial tendency of NiO grains and NiFe grains. However, as Ar pressure increased, interfacial diffusion at NiFe/NiO interface and oxygen content of NiO film increased, and consequently reduced the exchange anisotropy. We concluded that the flatten and abrupt interface and relatively low oxygen content of NiO layer are dominating factors for the exchange anisotropy in NiFe/NiO bilayer.
Multilayered films composed of disordered fcc-NiMn (Mn-54at.%) and Permalloy (Ni-78at. %) with fcc- texture show unidirectional exchange anisotropy below 100K even when thickness of NiMn layer is 0.8nm. Disordered fcc-NiMn alloys order antiferromagnetically at low temperature and they are paramagnetic at room temperature. The unidirectional anisotropy energy at 5K for 2.0nm-thick NiMn layer is 5×10-2erg/cm2. At room temperature, magnetization curves of multilayers with 5nm-thick Permalloy layers show NiMn layer thickness dependence suggesting canted interlayer magnetic coupling through paramagnetic NiMn layers at around 2nm.
The correlation between the antiferromagnetic (AF) grain volume, νAF and the exchange anisotropy is discussed for Ni-Fe/25 at% Ni-Mn system. In spite of various thickness combination of ferromagnetic (F) and AF layers, the unidirectional anisotropy constant, Jk commonly became large and saturated with increasing νAF. The substantial coercivity originated from the AF layer decreased and became constant with increasing νAF. These experimental results were well explained by a simple model based on Meiklejohn's single spin model. We concluded that increasing νAF is key to induce the exchange anisotropy effectively in F/AF bilayers.
The magnetisation reversal of polycrystalline permalloy/copper multilayers with antiferromagnetic couplingwas measured as a function of temperature. The magnetisation behavior is discussed in the relation to the exstence of ferromagnetic pinholes bridging neighbouring permalloy layers.
The bilayers consisting of PdCo (magnetostrictive alloy) and Fe (soft magnetic alloy), PdCo (x nm)/Fe (y nm) in the layer thickness range of 10 ≤ x ≤ 25 and 0 & le; y ≤ 30 have been fabricated A drastic magnetic softening is achieved for the bilayers that the PdCo layer thickness x ≤ 15 nm andthe Fe layer thickness y ≥ 20 nm, comparing with PdCo films. More than 70% of the saturated magnetostriction is obtained even at 50 Oe. The maximum magnetostriction of kn-abstract=the bilayers at 50 Oe is about -70 × 10-6 This drastic improvement of the magnetostriction response to the magnetic field occurs when both the PdCo and Fe magnetization are in-plane.
Mossbauer spectra and magnetization at different temperature and on hydrogenation for a series of Fe-Cr-Zr alloys are studied. The bimodal hyperfine field distributions are obtained by the fitting of Mossbauer spectra. Based on the hyperfine field distribution and the improved Langevin function, magnetization curves are fitted. Based on the located energy minimum of two single domain particles, hysteresis loop and spin-glass-like behavior can be explained. All of these experimental and theoretical results prove the existence of two-cluster.
The discovery of the first Fe-based ferromagnetic amorphous alloy in 1966 had made an impact on conventional magnetic materials because of its unique properties. Since then, a number of amorplious magnetic materials have been successfully developed and used in a wide variety of applications. A brief review of R & D activities on amorphous materials in China is given from the beginning to the present in a somewhat chronological order, followed by a brief introduction to their applications on electric and electronic industry. An analysis and a prospect of Chinese market of such amorplious materials are also presented.
(Fe, Co, Ni)-(Zr, M)-B (M=Nb, Ta, Ti) amorphous alloys exhibit a large supercooled liquid region (ΔTx) up to 90 K that have allowed us to prepare bulk amorphous samples with thickness up to 2 mm by mould casting method. These alloys have also good soft magnetic properties, i. e. saturation magnetisation (Bs) up to 1.1 T, coercive field (Hc)of 3 A/m and permeability of about 10000 at 500 Hz in the as-cast state. The Curie temperatures (Tc) of these amorphous alloys are between 513 and 573 K. The thermal and thermomagnetic annealing applied to (Fe, Co, Ni)70(Zr, M)10B20 (M=Nb, Ta, Ti) amorphous samples cause the change of their amorphous structure and magnetic properties. The obtaining of these bulk amorphous alloys with good soft magnetic properties will allow using them in many engineering applications.
Mössbauer investigations of Fe87Zr7Si4B2 nanocrystal line material were performed over the temperature range 4.2-675 K. Three well resolved spectral components have been found and attributed to bcc-Fe grains (with almost pure iron structure), residual amorphous matrix enriched with solute elements and interfaces formed at the grain-matrix boundaries. Thermal evolution of magnetic hyperfine parameters for these different structural phases are presented and discussed.
This study investigates the influence of quench rate during casting on surface crystallization and the magnetic properties of alloys with Al and Ti as impurities. The results showed that the surface crystallization of alloys containing these impurities was accelerated by a decrease in quench rate. The morphology of the crystallites formed are quite different in shape between Al and Ti. Further-more it is found that the soft magnetic properties are governed by only the crystalline layer thickness in which the crystallites are dispersed, regardless of species of impurities.
Magnetic cores with the permeability of approximately 150 were prepared by annealing Metglas 2605S3A ribbons in an O2 or N2 atmosphere, and effect of DC-bias field on their magnetic properties was studied. The atmosphere during annealing did not affect resultant magnetic properties of die cores. and the low permeability was estimated to be achieved by the partial crystallization and the resultant change in magnetization mode to the magnetization rotation mode. The fraction of crystallized part was estimated to be approximately 15 % in weight. A decrease in AC-permeability due to an application of DC-bias field was smaller than that of a Mn-Zn ferrite core with air-gap (μ=120) but larger than that of a Mo permalloy powder core (μ=130). The core loss, which is comparable with dial of a Co-based amorphous cut core (μ=200) and a Sendust powder core (μ=100), decreased with increasing the magnitude of DC-bias field at low frequencies such as 10 kHz and increased at high frequencies such as 150 kHz. This increase may be attributed to in-plane eddy current loss at high frequencies.
Crystallization process of amorphous Fe80P12C6Mo0.5 SiI. 5 alloy is observed at 733K by in-situ TEM. Results show that crystalline process of this alloy presents three-step type, i.e. incubation, phase separation and crystallization. Before precipitation of bcc-Fe,  and  diffraction rings of cubic-carbon appear first. With the increase of annealing time, these diffraction rings of cubic-carbon disappear. The bcc-Fe grains of Fe80P12C6Mo0.5Si1.5 and Fe79.5P12C6Cu0.5Mo0.5Si1.5 alloy, annealed at 673K, present different morphology. Copper is necessary in the formation of FePC based nanocrystalline alloy.
The structure and magnetic properties of Fe79.5P12C6 Cu0.5Mo0.5Si1.5 alloy is studied with ballistic galvanometer and by X-ray diffraction. Results show: after zero field annealing (ZFA) at 613K, nanocrystalline alloy having good soft magnetic properties of B800A/m=1. 4T, Hc=5.4 A/m, μm=128000 is formed. The grain size of bcc-Fe precipitates is around 22nm. The lattice parameter a0 of bcc-Fe is 0.28667nm, which is a little larger than that of pure iron. With the increase of annealing temperature, a0 decreases. Annealing time ta has little influence on a0. The good soft magnetic property is explained by the reduction of effective anisotropy constant.