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Although the magnetization reversal process in the permanent magnets has long been studied, it has not been fully revealed. The recent progress of the computational science realizes the atomistic calculations for the thermally activated magnetization reversal process in permanent magnets. In contrast, the experimental study on the magnetization reversal has remain to be the macroscopic evaluation. In this study, Nd-Fe-B hot-deformed magnets are micropatterned, and a staircase-like magnetization curve corresponding to the elemental domain-wall depinning event at each grain boundary is successfully observed. Each elemental domain-wall depinning event fluctuates with respect to thermal activation, and the stochastic analysis based on the Neel-Arrhenius model gives the energy barrier parameters H0 and E0 of each depinning event, which are the intrinsic domain-wall depinning field and energy barrier height, respectively. Three types of Nd-Fe-B hot-deformed magnets with different coercivities are adopted for this stochastic analysis. As a result, E0 exhibits very little dependence on H0, and its slope becomes steeper for the lower-coercivity magnet. The stochastic micromagnetics simulation based on the Landau-Lifshitz-Gilbert equation for the two-grain model with various inter-grain exchange coupling reproduces the experimentally observed relationship between E0 and H0. Moreover, the behavior for the lower-coercivity magnet can be explained by assuming the presence of a low magnetic anisotropy layer on the grain surface.

We report a precise measurement of the sensor behavior of the field effect transistor (FET) formed with the MoS2 channel when the channel part is exposed to Cl2 gas. The gas exposure and the electrical measurement of the MoS2 FET were executed with in situ ultrahigh-vacuum (UHV) conditions in which the surface analysis techniques were equipped. This makes it possible to detect how much sensitivity the MoS2 FET can provide and understand the surface properties. With the Cl2 gas exposure to the channel, the plot of the drain current versus the gate voltage (Id–Vg curve) shifts monotonically toward the positive direction of Vg, suggesting that the adsorbate acts as an electron acceptor. The Id–Vg shifts are numerically estimated by measuring the onset of Id (threshold voltage, Vth) and the mobility as a function of the dosing amounts of the Cl2 gas. The behaviors of both the Vth shift and the mobility with the Cl2 dosing amount can be fitted with the Langmuir adsorption kinetics, which is typically seen in the uptake curve of molecule adsorption onto well-defined surfaces. This can be accounted for by a model where an impinging molecule occupies an empty site with a certain probability, and each adsorbate receives a certain amount of negative charge from the MoS2 surface up to the monolayer coverage. The charge transfer makes the Vth shifts. In addition, the mobility is reduced by the enhancement of the Coulomb scattering for the electron flow in the MoS2 channel by the accumulated charge. From the thermal desorption spectroscopy (TDS) measurement and density functional theory (DFT) calculations, we concluded that the adsorbate that is responsible for the change of the FET property is the Cl atom that is dissociated from the Cl2 molecule. The monotonic shift of Vth with the coverage suggests that the MoS2 device sensor has a good sensitivity to detect 10–3 monolayers (ML) of adsorption corresponding to the ppb level sensor with an activation time of 1 s.

A Ga-doped Nd-Fe-B sintered magnet has attracted significant attention as a heavy-rare-earth-free high-performance magnet. We have studied the temperature dependent magnetization reversal process of a Ga-doped Nd-Fe-B sintered magnet based on the first-order reversal curve (FORC) analysis. The FORC diagram pattern of the Ga-doped Nd-Fe-B sintered magnet changes from single spot in the high field region at room temperature to double spots in the low and high field regions at 200 °C, indicating that the dominant magnetization reversal process changes from single domain type to multidomain type. The single domain magnetization reversal at room temperature is well confirmed by using the soft X-ray magnetic circular dichroism microscopy observation. This change in the magnetization reversal process is well discussed by the temperature dependent local demagnetization field and the saturation field of multidomain state. Moreover, we have demonstrated the quantitative analysis of the FORC diagram pattern, which makes a deeper understanding of the magnetization reversal process of the Ga-doped Nd-Fe-B sintered magnet.

First-order reversal curve (FORC) diagram, which visualizes the variation of magnetic susceptibility on a field plane, has been applied to a Nd-Fe-B sintered magnet. The FORC diagram exhibits the characteristic behavior of two remarkable spots in low-field and high-field regions. The high-field FORC spot corresponds to the irreversible magnetization reversal at a coercive field, whereas the low-field FORC spot indicates the appearance of a large magnetic susceptibility state during the demagnetization process. Moreover, this low-field FORC spot becomes dominant at high temperature, accompanied by a significant reduction in coercivity. These results suggest that the low-field FORC spot has a strong correlation with the degradation of magnetic properties of a Nd-Fe-B sintered magnet. To clarify the actual magnetization reversal processes corresponding to these two FORC spots, soft X-ray magnetic circular dichroism (XMCD) microscopy observation was employed with similar field sequences of the FORC measurements. Consequently, the low-field FORC spot is mainly attributed to the domain wall motion in multi-domain grains, whereas the high-field FORC spot corresponds to the magnetization reversal of single-domain grains. These indicate that a FORC diagram is a powerful evaluation method for the magnetization reversal processes of permanent magnets.

There is a growing interest in the development of rare-earth element-free hard magnets. The L10 FeNi phase found in Fe-based meteorites is promising based on its high-magnetocrystalline anisotropy and saturation magnetization. Not only the production, but also the characterization of L10 FeNi phase is challenging due to similar X-ray scattering factors of Fe and Ni. Here, we report on the confirmation of L10 FeNi phase precipitated in a multi-phase FeNiSiBPCu alloy by anomalous X-ray diffraction (AXRD). This is a powerful technique, which can differentiate between ordered and disordered phases along with the elements present in a phase. We measured integrated X-ray intensity with energy near the Fe (~7–7.2 keV) and Ni (8.25–8.4 keV) absorption edges for superlattice and fundamental reflections of L10 FeNi. A drastic change in integrated intensity with energy of X-ray was observed. Increase in intensity around superlattice reflection at Ni-absorption edge clearly confirms the presence of a chemically ordered L10 FeNi phase, but the results obtained at Fe edge are surprising. The analysis of AXRD results suggested that (110) diffraction peak of Fe2B phase overlaps with (001) of L10 FeNi. Understanding gained from AXRD results also allows us to estimate the long-range order parameter (S) from X-ray diffraction measurements.

[Co (0.29 nm)/Ni (0.71 nm)]10 multilayers were deposited on Ta (30 nm) and Pt (30 nm) buffer layers, and the variation of the magnetization dynamics by the adsorption of Fe3O4 nanoparticles was studied by vector network analyzer—ferromagnetic resonance method. The surface roughness of the Co/Ni multilayer was 0.52 nm, and significantly increased after the adsorption of the Fe3O4 nanoparticles which was captured by large field gradient on the demagnetized Co/Ni multilayer. The anisotropy field $H_{k}$ , damping constant $\alpha $ , and anisotropy distribution $\Delta H_{k}$ of the Co/Ni on Ta buffer layer were 2.6 kOe, 0.012, and 0.32 kOe, respectively. By adsorbing of the Fe3O4 nanoparticles, the stray field from the nanoparticles $H_{{\text {np}}}$ was applied to the Co/Ni, and $H_{k} + {H}_{{\text {np}}}$ was estimated to increase to 3.7 kOe. Moreover, $\alpha $ and $\Delta H_{k}$ also increased to 0.020 and 0.42 kOe by the adsorption, respectively. Similarly, $H_{k} + H_{\mathrm{np}}$ , $\alpha $ , $\Delta H_{k}$ of Pt buffered Co/Ni also increased from 2.4 kOe, 0.033, 0.43 kOe to 4.2 kOe, 0.055, 0.53 kOe, respectively. These results suggest that the adsorption of Fe3O4 nanoparticles significantly modifies the magnetization dynamics of Co/Ni multilayer.

Understanding of magnetization behavior in magnetic nanostructures is a key issue for future magnetic/spintronic devices. Time-resolved X-ray magnetic circular dichroism (XMCD) is a powerful measurement technique with potential of nanometer spatial resolution, picosecond time resolution, and element selectivity. We have carried out time and spatially resolved XMCD microscopy measurement on a Co/Pt multilayer dot by detecting XMCD at the Pt $L_{3}$ edge at BL39XU of SPring-8 using hard X-ray. Transient magnetic response of Co/Pt multilayer dots with diameter of $2.6~\mu \text{m}$ was investigated against pulsed RF field with frequency around 2.5 GHz and the maximum amplitude of about 400 Oe. By synchronizing excitation RF field pulse with X-ray pulses, the growth of magnetization precession of the induced Pt magnetic moment in the dot was clearly observed with sub-100 ps time resolution and submicrometer spatial resolution. The developed measurement setup can be applicable for a wide range of studies for time-resolved hard X-ray experiments.

Magnetocapacitance (MC) effect, observed in a wide range of materials and devices, such as multiferroic materials and spintronic devices, has received considerable attention due to its interesting physical properties and practical applications. A normal MC effect exhibits a higher capacitance when spins in the electrodes are parallel to each other and a lower capacitance when spins are antiparallel. Here we report an inverse tunnel magnetocapacitance (TMC) effect for the first time in Fe/AlOx/Fe3O4 magnetic tunnel junctions (MTJs). The inverse TMC reaches up to 11.4% at room temperature and the robustness of spin polarization is revealed in the bias dependence of the inverse TMC. Excellent agreement between theory and experiment is achieved for the entire applied frequency range and the wide bipolar bias regions using Debye-Fröhlich model (combined with the Zhang formula and parabolic barrier approximation) and spin-dependent drift-diffusion model. Furthermore, our theoretical calculations predict that the inverse TMC effect could potentially reach 150% in MTJs with a positive and negative spin polarization of 65% and −42%, respectively. These theoretical and experimental findings provide a new insight into both static and dynamic spin-dependent transports. They will open up broader opportunities for device applications, such as magnetic logic circuits and multi-valued memory devices.

One of the most important achievements in the field of spintronics is the development of magnetic tunnel junctions (MTJs). MTJs exhibit a large tunneling magnetoresistance (TMR). However, TMR is strongly dependent on biasing voltage, generally, decreasing with applying bias. The rapid decay of TMR was a major deficiency of MTJs. Here we report a new phenomenon at room temperature, in which the tunneling magnetocapacitance (TMC) increases with biasing voltage in an MTJ system based on Co40Fe40B20/MgO/Co40Fe40B20. We have observed a maximum TMC value of 102% under appropriate biasing, which is the largest voltage-induced TMC effect ever reported for MTJs. We have found excellent agreement between theory and experiment for the bipolar biasing regions using Debye-Fröhlich model combined with quartic barrier approximation and spin-dependent drift-diffusion model. Based on our calculation, we predict that the voltage-induced TMC ratio could reach 1100% in MTJs with a corresponding TMR value of 604%. Our work has provided a new understanding on the voltage-induced AC spin-dependent transport in MTJs. The results reported here may open a novel pathway for spintronics applications, e.g., non-volatile memories and spin logic circuits.

We investigate the microwave spectroscopies of a micrometer-sized single permalloy (Py) chiral structure on coplanar waveguides (CPWs). Under an external dc magnetic field applied in a direction perpendicular to the microwave propagation, the Py chiral structure loaded on the center of the CPW signal line shows Kittel-mode ferromagnetic resonance. Contrastingly, the structure on the signal-line edge highlights two additional resonances: spin-wave resonance at a higher frequency, and unique resonance at a lower frequency of approximately 7.8 GHz. The resonance signal at 7.8 GHz originates from magnetically induced, geometry-driven resonance, although the resonance frequency does not depend on the external magnetic field. Moreover, the displacement of the Py structures on the signal line results in nonreciprocal microwave transmission, which is traced back to the edge-guide mode.

In this paper, we report that W/Fe/W (001) epitaxial trilayer films exhibit very large negative uniaxial magnetic anisotropy $K_{u}$ . The magnitude of $K_{u}$ increases with decreasing the Fe layer thickness and also exhibits significant temperature dependence varying from $-2.1 \times 10^{7}$ erg/cc at 300 K to $-3.5 \times 10^{7}$ erg/cc at 10 K for the Fe layer thickness of 0.5 nm. The large negative $K_{u}$ is attributable to interface magnetic anisotropy in nature at the W/Fe interface and can be quantitatively reproduced by the firstprinciples calculation. The X-ray magnetic circular dichroism measurement at room temperature has revealed that the interfacial W atom is polarized in antiparallel with the magnetic moment of Fe. The induced magnetic moment of the interfacial W is almost the half of the values obtained by the first-principles calculation and the previous experiment at low temperature. This small induced W moment may be ascribed to the significant temperature dependence of the negative $K_{u}$ .

We examined microwave-assisted switching properties of an antiferromagnetically coupled (AFC) granular perpendicular medium consisting of CoCrPt–TiO2(5)/Co(0.7)/Ru(0.9)/Co(0.7)/CoCrPt–TiO2(3) (in nanometers). In a saturation remanent state, the magnetization of the lower CoCrPt–TiO2 + Co layer switched its direction to form AFC with that of the upper layer because of a thin-film thickness. We assessed the microwave-assistance effect on magnetization switching from the remanent state to the saturation state of the thick upper layer using an anomalous Hall effect. The reduction of a switching field was most enhanced by the application of microwaves of 10 GHz frequency. The switching field reduction by microwave assistance for the AFC medium, obtained by compensating a thermal agitation effect, was estimated as 26%.

Magnetization reversal in a permanent magnet takes place through multiple and simultaneous events of nucleation and domain wall depinning. Thus, detection and analysis of elemental magnetization reversal events are essentially important to understand the coercivity mechanism of a permanent magnet. In this study, we have fabricated a micro-patterned Nd-Fe-B hot-deformed magnet using mechanical polishing and focused ion beam, and anomalous Hall effect (AHE) detection has been adopted to measure the magnetization reversal of the sample. During the micro-patterning process, the degradation of magnetic property is carefully evaluated. Consequently, the micro-patterned Nd-Fe-B hot-deformed magnet with the thick of 5 μm and the width of 13 μm is fabricated, and subsequently, the discrete steps on the AHE curve are successfully detected. The magnetization reversal unit size estimated from the step height is ∼1 μm2, which is almost the same as observed in the magneto-optical Kerr microscopy. We have clearly demonstrated that this technique has significant potential to study the physical nature of elemental magnetization reversal events in permanent magnets.

In this paper, we review the theory and experiment on microwave-assisted magnetization switching in perpendicular magnetic nanodots. Within the framework of the single-macrospin model, the switching condition under radio frequency fields can be analytically derived from the steady-state solutions of the Landau-Lifshitz-Gilbert equation. When the Gilbert damping is not so large, this analysis perfectly coincides with the Stoner-Wohlfarth model under the rotating frame. This calculation also predicts the critical frequency above which no microwave assistance effect is operative. While the above analysis almost explains the experimental results on nanodots of a Co/Pt multilayer, the nanodots exhibits unusual size-dependent switching behaviors. For the dot as small as 50 nm, the switching behaviors agree with the analytical calculations based on the single-macrospin model. In contrast, for the dot diameter , the significantly enhanced assistance effect is observed. This enhancement for larger dot can be explained by excitation of spatially nonuniform precessional motion in the dots.

Fe–B–P submicron particle chains and (Ni0.6Zn0.4)Fe2O4 nanoparticles were synthesized by chemical methods. (Ni0.6Zn0.4)Fe2O4 nanoparticles were used to fill in the space among Fe–B–P chains under a magnetic field. The synthetic composite of Fe–B–P chains filled with 20 vol.% (Ni0.6Zn0.4)Fe2O4 nanoparticles exhibits the highest intrinsic permeability(142). It is due to the enhanced performance of Fe–B–P particle chains and the effect of (Ni0.6Zn0.4)Fe2O4 nanoparticles, which both decrease the demagnetization field. The composite film also shows a better power loss feature on coplanar transmission line than pure Fe–B–P chains, and the resonance frequencies of the composite films on coplanar line shift to about 20–30 GHz, which is caused by a large demagnetizing field due to the narrow line width of coplanar line.

We investigate the ferromagnetic resonance (FMR) of a single chiral structure of a ferromagnetic metal—the magnetochiral (MCh) metamolecule. Using a strain-driven self-coiling technique, micrometer-sized MCh metamolecules of metallic permalloy (Py) are fabricated without any residual Py films. The magnetization curves of ten Py MCh metamolecules obtained by an alternating gradient magnetometer show soft magnetic behavior. In cavity FMR with a magnetic-field sweep and coplanar-waveguide (CPW) FMR with a frequency sweep, the Kittel-mode FMR of the single Py metamolecule is observed. The CPW-FMR results, which are consistent with the cavity-FMR results, bring about the effective g factor, effective magnetization, and Gilbert damping of the single metamolecule. Together with calculations using these parameters, the angle-resolved cavity FMR reveals that the magnetization in the Py MCh metamolecule is most likely to be the hollow-bar type of configuration when the external magnetic field is applied parallel to the chiral axis, although the expected magnetization state at remanence is the corkscrew type of configuration.

Amorphous CoxFe1-x-B particles with magnetic softness were fabricated by chemical reduction of metal ions. Fabrication conditions to obtain particles with good magnetic softness are described. CoxFe 1-x-B particles with x= 0.90-0.95 exhibit superb softness because of their nearly zero-magnetostrictive property. The soft properties of the particles are thermally stable compared to other compositions such as Fe-B-P or Co50 Fe50-B. Chains of CoxFe1-x-B particles with x=0.95 produced in a magnetic field were studied in detail. The high permeability feature associated with the high aspect ratio of the chain shape exhibits only a slight change after annealing up to 400 degrees. The frequency dispersion of initial permeability exhibits two resonance peaks that are ascribed to the shape anisotropy of the chains.

Gilbert damping constants α of Co/Pd multilayers with various layered structures were estimated by time resolved magneto-optical Kerr effect. The [Co(tCo)/Pd(tPd)]6 multilayers exhibiting a perpendicular magnetic anisotropy (PMA) were prepared by dc magnetron sputtering on a Pd (1 nm)/Ta (30 nm)/oxidized Si substrate. The PMA of the multilayer having tCo/tPd=0.55 increased with decreasing the bilayer period, tCo+tPd, while all the multilayers showed almost the same α of 0.09. The same trend was seen for Co/Ni multilayers with a constant tCo/tNi, although the values of α are different, i.e., 0.035 for Co/Ni . From the estimation of the damping α of the multilayers with various tCo/tPd, the α was confirmed to be enhanced when the ratio tCo/tPd becomes lower than 0.8. Moreover, the linear relationship between the α and tPd/tCo was found. These results suggest that the damping α of both Co/Pd and Co/Ni multilayers are not closely correlated with their PMA, and mainly determined by the composition of the multilayers.

Amorphous Fe-P-B particles with submicron sizes were synthesized by chemical precipitation in aqueous solutions. The particles having a spherical shape exhibit good magnetic softness and high saturation magnetization. When they are precipitated in a magnetic field, they are connected to each other to form a chain shape. The high aspect ratio of the chains reduces appreciably the demagnetization field associated with isolated particles, resulting in significant improvement of high permeability performance. In this paper, investigations on the external and internal structures of the chains, uniaxial anisotropy caused by aligning the chains in an external magnetic field, frequency dispersion of permeability, and thermal change of the high permeability feature are presented. Finally, comparison of permeability for particles with various sizes is made with the present chain samples. In addition to the superior high permeability feature compared to other magnetically soft particles, the chains exhibit low loss characteristics at high frequencies up to a few GHz. It is also demonstrated that permeability is improved by annealing at 150°C in vacuum. These results suggest that the particle chains have a high potential for high-frequency applications such as inductor cores and electromagnetic noise absorbers.

Co/Ni multilayers with a stack of Ta (2 nm)/[Co (tCo)/Ni (tNi)] N/Ta (30 nm) were prepared by dc magnetron sputtering, and their magnetization dynamics were measured by time-resolved magneto-optical Kerr effect (TRMOKE). The total thickness of the multilayer and perpendicular anisotropy were varied by changing the bilayer period d = tCo+ tNi and number of repeats N while tNi/tCo was kept at a constant of 2.5. The TRMOKE measurements show clear damped oscillation of the magnetization of Co/Ni multilayers after the pump pulse illumination, and the damping constant α of the Co/Ni multilayers was estimated from the TRMOKE waveform. The estimated α was found to be independent both on total thickness and anisotropy field of the multilayer and was estimated to be ~ 0.035 for all the multilayers. This means that the use of Ta capping and buffer layers is effective to evaluate intrinsic damping constant of the Co/Ni multilayer, and that independent control of α and perpendicular anisotropy are possible for the magnetic multilayers.

Magnetically soft amorphous particles were successfully synthesized in aqueous solutions. The advantages of the particles are their high saturation magnetization and submicron size. In addition to the original synthesizing process, particle precipitation in a magnetic field is studied. In the process of precipitation in the magnetic field the particles are bonded into long chains leading to an appreciable reduction of the demagnetizing field that has been an obstacle to the high-permeability performance of soft magnetic particles. The microstructures, magnetic softness of the chains, and significant enhancement of the permeability in the frequency range 0.05∼10 GHz are demonstrated.

Submicron-size amorphous particles were produced chemically from aqueous solutions. The particles in the as-made state exhibit a high saturation magnetization and magnetic softness almost equivalent to that of much larger amorphous particles produced by water atmizing. Platinum ions work effectively to control the particle size without losing magnetic softness. Magnetic softness observed for the as-made particles becomes degraded slightly by annealing. A calculation of eddy current within spheres predicts no eddy current loss even at 100 MHz for 0.3-mum particles, whereas initial permeability measurements exhibit slight indication of magnetic loss due to the broad spin resonance profile extending from 100 MHz to 10 GHz.

We have investigated the relationship between the crystal structure and the magnetic anisotropy constant of epitaxially grown Fe/Co multilayers (ML). The Fe/Co ML grown on a Ag (100) underlayer at ambient temperature exhibits body centered cubic (bcc) structure with (100) orientation for the stacking period λ less than 15 nm. The saturation field along the film normal is much larger than the demagnetization field 4πMs, indicating negatively large magnetic anisotropy Ku. The negative Ku takes the peak value as large as −1×107 erg/cc at λ = 0.75 nm. This behavior of Ku against λ is very similar to that reported for Fe/Co (110) polycrystalline ML [Vas'ko et al., Appl. Phys. Lett. 89, 092592 (2006)]. Moreover, slight lattice distortion is observed, but the magnetoelastic contribution is much smaller than the negative Ku. These results lead to the conclusion that the negative Ku of Fe/Co ML is attributable to the interfacial magnetic anisotropy with weak crystal orientation dependence.

Fine-particle composites consisting of high-permeability particles with a large size difference exhibit enhanced initial permeability. From an analysis of the initial permeability of a composite that includes Fe (1 micron) particles as a main component, we found that the microscopic demagnetizing field imposed on the particles is appreciably reduced, allowing enhancement of the initial permeability up to the intrinsic permeability of Fe particles. The significance of this effect is exemplified using composites that include Ni50Fe50 (6 microns) and amorphous Fe-Si-B-Cr (3 microns) particles. According to a calculation of the eddy current in spheres with high permeability, reduction of the particle size to less than 1 micron is essential for further improvement of the high-frequency performance of particle composites.

A pulse generator with large amplitude of 160 V and fast rise time of less than 0.4 ns has been built using a coaxial cable as a capacitor. By combining with the anomalous Hall effect technique for a single magnetic nanodot, magnetization response of one Co/Pt nanodot of 400 nm in diameter to the pulse was examined. By applying a pulse field with the maximum amplitude of 740 Oe and the duration of 10 ns, magnetization switching of the dot by the pulse was successfully observed. The pulse amplitude dependence of switching field suggested that the pulse field and the dc bias field could be treated as a simple summation of the both fields in the time scale of 10 ns. All the results of magnetization switching by the pulse field could be explained qualitatively by classical thermal relaxation process.

We have studied the additive effects of AlN and MgO on L1 0 -FePt nanoparticles by co-sputtering FePt and AlN (or MgO) on MgO(100) substrates at 973 K. Good epitaxial growth of FePt was confirmed both for AlN and MgO. With the increase of the additive content, the long range order (LRO) of L1 0 phase appeared to increase for AIN, whereas it was suppressed for MgO. Morphological observation by addition of AlN, well-isolated FePt particles became to connect each other, and finally formed a maze-like structure. On the other hand, the morphology of FePt particles was hardly affected by addition of MgO.

Thin disordered layer can be formed by sputter-deposition of alumina on fully ordered L1 0 FePt nanoparticle assembly, due to plasma damage. The thickness of the disordered layer can be tuned by the sputtering power and deposition time of the alumina target. This partial disordering causes substantial decrease in the coercivity, which may be effective to adjust very high switching field of L1 0 FePt to practical magnetic recording systems.

The magnetic anisotropy of CoPtCr-SiO/sub 2/ perpendicular recording media, including higher energy terms, was studied as a function of film composition and seed layer materials. All series of CoPtCr films with various Cr content, deposited on Ru seed layers, show maximum values of total anisotropy K/sub u/ at 25-30 at%Pt. The maximum value for CoPt(Cr=0) films reaches /spl sim/15/spl times/10/sup 6/ erg/cm/sup 3/. The addition of SiO/sub 2/ to the CoPtCr films reduces the grain K/sub u/, however the grain K/sub u/ maintains a large value of 8/spl times/10/sup 6/ erg/cm/sup 3/ even when 10at%SiO/sub 2/ is added to (Co/sub 90/Cr/sub 10/)/sub 80/Pt/sub 20/, for instance, which indicates the high-potential thermal stability. Theoretical calculations for media designs of 400 Gbits/in/sup 2/ revealed that the ratio of the high-energy anisotropy term K/sub u2/ to K/sub u1/(K/sub u/=K/sub u1/+K/sub u2/) is required to be 0.2-0.35 to enhance the energy barrier for the remanent state, without a notable change in switching field. The films deposited on Ru seed layers were found to show negligibly small K/sub u2/ values, however, the values of K/sub u1/ and K/sub u2/ vary significantly with the seed layer material used. K/sub u1/ decreases almost linearly as the K/sub u2/ value increases. It is concluded that CoPtCr films have a sufficient potential in the values of K/sub u1/ and K/sub u2/ for high-density perpendicular media.

Structural properties of CoPtCr–SiO2 magnetic recording films grown on Ru or Pt seed layers prepared by UHV-magnetron sputtering were studied by high resolution transmission electron microscopy (HRTEM), electron energy loss spectroscopy (EELS) and energy filtered transmission electron microscopy (EFTEM). CoPtCr grown on Ru seed layers together with SiO2 forms a well-isolated structure composed of CoPtCr fine grains of 10 nm diameter surrounded by amorphous SiO2, whereas CoPtCr grown on Pt seed layers together with SiO2 forms a network structure composed of CoPtCr crystal of 5 nm size. These structural features made differences in their magnetic properties. The HRTEM and EFTEM studies revealed that cylindrical crystalline grains composed of CoPtCr and Ru are formed for CoPtCr–SiO2/Ru samples, whereas SiO2 are aggregated around the boundary between relatively large Pt grains and magnetic layers without obstructing the epitaxial growth of CoPtCr on Pt, not resulting in the cylindrical CoPtCr grains. Lattice spacings of CoPtCr grown on Pt with SiO2 are 0.7% expanded in comparison with CoPtCr grown on Pt without SiO2. The EELS studies suggested that Co and Cr atoms are partly oxidized by SiO2 addition for both samples and Cr atoms are more oxidized for CoPtCr–SiO2/Pt samples.

We studied the c-axis direction and ordering process of L10-FePt thin films during thermal annealing. For the thinner (5 and 10 nm) samples, rapid annealing clearly promoted (001) orientation with higher L10 ordering. However, for the thicker (50 nm) samples, (111) orientation was dominant independent of the annealing conditions. We suggest that stress direction and its relaxation during thermal annealing strongly relate to these remarkable changes of orientation and L10-ordering.

Magnetic domain structure of FePt(001) films, which show huge magnetocrystalline anisotropy, was observed by electron holography and Lorentz microscopy. Although these methods have advantages for the microanalysis of magnetic domains, e.g., the high spatial resolution, detection of the magnetic signal is rather difficult when the magnetization vector is parallel to the incident electron beam like the case of FePt(001) films. Here we demonstrate that the intensive observations are possible when the specimen is tilted in a microscope so that the magnetic flux perpendicular to the incident beam is generated. The holography experiment using the cross-sectioned specimen also provided useful information about the stray magnetic field of the FePt(001) films.

In order to clarify the formation process of L10 Fe–Pt ordered phase in Fe (tFe)/Pt (tPt) multilayers, we have evaluated the activation energy of ordering (QS) and of atomic interdiffusion at Fe/Pt interfaces (QD). QS for the multilayers takes a minimum value of ∼0.7 eV when tFe=tPt, much lower than that of Fe–Pt disordered alloy films (1.2 eV). This value is almost the same with the activation energy QD of atomic interdiffusion at Fe/Pt interfaces. From these results, it is concluded that the interdiffusion at Fe/Pt interfaces which occurs at relatively low temperature dominates the formation process of L10 Fe–Pt in Fe/Pt multilayers.

We fabricated magnetic rectangular block arrays of 130 and 260 Gblock/in2 by using focused ion beam lithography. The ratios R of the total block area to the array area are 0.73 and 0.64, respectively. The magnetic domain boundaries of the arrays run along the grooves between the blocks. Each block has a single domain structure and perpendicular magnetic anisotropy. The pattening increased the squareness from 0.2 of the continuous film to 0.87 of the array with 130 Gblock/in2. Application of the block arrays to high-density patterned magnetic recording media is discussed.

Fe microparticle composites with different nanoparticles were prepared using Ni-Zn ferrite and Fe-B-P amorphous nanoparticles. Both additions into iron microparticles significantly increase magnetic permeability, whereas Fe-FeBP composite exhibits more advantages than Fe-(Ni0.6Zn0.4)Fe2O4 composite due to higher saturation magnetization (Ms). The magnetic field range with high permeability is about 0-600 Oe for Fe-FeBP composite, whereas it decreases to 0-80 Oe for Fe-(Ni0.6Zn0.4)Fe2O4 composite. The permeability of Fe-FeBP composite remains high up to about 1 GHz and the resonance frequency is about 2 GHz, which is higher than that of Fe-(Ni0.6Zn0.4)Fe2O4 composite.

In the present study, we have prepared and investigated Co/sub 100-x/Pt/sub x/ (0/spl les//spl times//spl les/40) fine particles with the average diameter of D=3/spl sim/40 nm. At a fixed D/spl sim/10 nm, the room temperature coercivity H/sub c/ increases with the Pt content x and takes a maximum value of 1000 Oe at x/spl sim/25 at.% for 3D random assemblies of the particles. Such remarkable enhancement of the coercivity due to Pt is attributed to very strong magnetic anisotropy, as evaluated by the law of approach to saturation. At x/spl sim/25 at.%, H/sub c/ increases with D due to suppression of thermal agitation and takes a maximum of 4000 Oe around at D/spl sim/15 nm. Micromagnetic calculations taking into account dipolar interactions between particles have verified that the magnetic behaviors of Co/sub 75/Pt/sub 25/ fine particles can be explained by the coherent rotation model.

We have studied the effect of Sm on the magnetic surface anisotropy (MSA) of Pd/Co100−xSmx/Pd (111) trilayers, where Sm content x was varied from 0 to 11. All samples show perpendicular anisotropy due to the strong MSA at the interfaces. The MSA significantly increases with x and attains a maximum value of 0.60 erg/cm2 at x≃8.3, which is 36% larger than that of pure Co (x=0). The volume term of the magnetic anisotropy shows a similar behavior as the MSA. The appreciable increase in MSA is considered to be due to the enhancement of orbital moment of Co by the addition of Sm.

In this study well-ordered L10-FePt nanoparticles were formed on MgO underlayers. Very thin FePt films (thickness: 2 ∼ 10 nm) formed islands with diameters of about 10 nm at a substrate temperature of TS =520 °C. Resistivity measurements showed that the islands are well isolated. The isolation was confirmed in a SEM observation. MgO underlayers grown at ambient temperature induce (001) orientation of subsequently deposited FePt. These FePt films in island structure have coercivities as high as 5 kOe even for a nominal thickness of 2 nm.