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The effects of the coating surface orientation of the α-Fe soft magnetic layer on the Sm(Fe0.8Co0.2)12 hard magnetic phase and the volume fraction of α-Fe, VFe, on the maximum energy product, ( BH)max of exchange-coupled Sm(Fe0.8Co0.2)12/α-Fe nanocomposite magnet particles were micromagnetics OOMMF package was systematically investigated. The ( BH)max of the reference model, Sm(Fe0.8Co0.2)12 particles without Fe layer, was 630 kJ/m3. In contrast, in the nanocomposite magnet particle model with soft magnetic layers on both sides of the hard magnetic phase, ( BH)max reached a maximum value of 657 kJ/m3 at VFe = 12% (Fe layer thickness, tFe = 2 nm). In the model with α-Fe coating on the top and bottom surfaces of the hard magnetic phase, ( BH)max = 636 kJ/m3 at VFe = 4% ( tFe = 2 nm). Furthermore, the coating of the soft magnetic phase on both sides of the hard phase particles reduces the magnitude of the demagnetizing field, Hd of the nanocomposite magnet particles, indicating that the side coating of the soft magnetic phase is effective in increasing ( BH)max. These findings allow for a greater degree of freedom in the design of nanocomposite magnets by adjusting not only the VFe volume fraction of the hard/soft phases but also their arrangement.

Magnetization curves for Pr2Fe14B single crystals were measured between 300 K and 900 K. The saturation magnetization Ms along the [1 0 0] direction was found to be 3% to 6% smaller than that for the [0 0 1] direction, not only at 300 K but also up to the Curie temperature. Published magnetization curves for Tm2Fe14B single crystals were reexamined, in which Ms along the [0 0 1] direction exceeds that for the [1 0 0] direction. We attributed these differences in Ms to the reduction of the rare-earth (R) moment when forced to be aligned along the hard direction by external fields. Significant anisotropy was observed in the paramagnetic susceptibility χ up to 900 K in the Pr2Fe14B (R = Pr) system. Based on the crystalline electric field parameters for R = Pr and Tm systems obtained by first-principles calculations, we numerically evaluated the magnetization and paramagnetic susceptibility at high temperatures. The differences in Ms and χ obtained from the calculation were in good agreement with the experiments. We found that the reduction rate for the Pr moment at the 4f site is much smaller than that at the 4 g site. This result suggests a crucial decrease in the local magnetic anisotropy at the Pr(4f) site.

Magnetization curves for Nd2Fe14B single crystals were measured between 300 K and 900 K. The saturation magnetization Ms along the [100] direction was found to be 2% to 4% smaller than that for the [001] direction, not only at 300 K but also up to the Curie temperature. We attributed this difference in Ms to the reduction of the Nd moment when forced to be aligned by external fields. Significant anisotropy was observed in the paramagnetic susceptibility χ up to 900 K. Based on the crystalline electric field parameters for Nd2Fe14B obtained by first-principles calculation, we calculated the magnetization and paramagnetic susceptibility χ. The difference in Ms and χ obtained from the calculation was in good agreement with the experiment. We found that the reduction rates for the Nd moments at 4f site are much smaller than that for the Nd moments at 4g site. This result therefore suggests a significant deterioration of local magnetic anisotropy at the Nd(4f) site even at elevated temperatures.

The Nd-Fe-B/Mo/Fe-Co multilayered films on MgO(001) were fabricated by UHV sputtering method. The as-deposited films showed soft magnetic properties with weak perpendicular magnetic anisotropy, and after annealing above 650°C, these films showed in-plane magnetic anisotropy, good squareness, and hard magnetic properties with high coercivity of about 8 kOe. The (220) peak of Nd2Fe14B was identified in the XRD pattern after annealing of the film, which means that the c-axis, which is the easy axis of magnetization, points in the plane of the film, consistent with the measurement of the magnetization curve. The positive peak of ΔM plot of in-plane direction of the film annealed at 800°C was shown. This result suggests existence of exchange coupling between the Nd-Fe-B and Fe-Co layers in the in-plane anisotropic multilayered film with monoatomic Mo interlayer.

Dielectric and magnetic properties of BiFeO3 samples, co-doped with Gd or Ba and Ti in place of Bi and Fe, respectively, were investigated. The bulk powder samples of nominal compositions of Bi0.9Gd0.1Fe1–xTixO3 and Bi0.7Ba0.3Fe1-xTixO3 (x=0.00-0.25) ceramics were synthesized by conventional solid state reaction technique. The as prepared ceramics showed improved dielectric and magnetic properties. Also, ultrafine nanoparticles of the samples were prepared by milling assisted ultrasonic fragmentation of the bulk powder. The particles size was studied as a function of sonication time with TEM imaging and electron diffraction. These confirmed the formation of a large fraction of single-crystalline Bi0.9Gd0.1Fe1–xTixO3 nanoparticles with a mean size of 11-13 nm. The synthesized nanoparticles exhibit an improved magnetic behavior compared to their bulk counterparts at room temperature. The preparation and characterization of bulk ceramics as well as their nanoparticles were reported.

The Nd-Fe-B/La thin films were deposited on the Al2O3(0001) substrate in order to investigate the effect of rare earth overlayer on the coercivity Hc. Highly textured Nd2Fe14B grains were grown by inserting the Mo(111) single crystal buffer layer. By depositing the La overlayer onto Nd2Fe14B thin films and subsequently post-annealing at 470 C, the Hc value increased from about 10.5 kOe to 15.0 kOe. The amount of Hc increase by the combination of the La coating and post-annealing was about 4.5 kOe. After the post annealing, La oxide (hcp La2O3) was formed in the La layer, which was confirmed by means of XRD and SIMS depth profile measurements.

We fabricated α-Fe(100)/Nd2Fe14B(001) bilayer films with different thicknesses values of the α-Fe layer on MgO(100) substrates by using an ultra-high-vacuum (UHV) magnetron sputtering system. The exchange coupling constant at the heterointerfaces of α-Fe(100)/Nd2Fe14B(001) was evaluated by analyzing the magnetization curves and the ferromagnetic resonance (FMR) spectra. We observed a significant lower shift of the α-Fe resonance field compared to that of the α-Fe single layer irrespective of the Fe-layer thickness, which suggests the existence of an internal field owing to a positive exchange coupling between the α-Fe(100) and the Nd2Fe14B(001) layers.

We fabricated a model interface system, which consised of a Nd2Fe14B layer with Dy overlayers, in order to study the relationship between the microstructure near the interface and the coercivity. The coercivity H c of the 1-µm-thick Nd-Fe-B films with a Dy overlayer was enhanced by thermal diffusion of Dy atoms from the film’s surface into the Nd-Fe-B layer. The Nd-Fe-B/Dy films annealed at 700 °C showed a significant increase in the H c of up to about 17 kOe. The maximum increase in the value of the coercivity ΔH c of the annealed films with a Dy overlayer was approximately 13 kOe. The XRD measurement suggested the existence of rare-earth oxides (NdO and Dy2O3) in the Dy-coated films with high value of the ΔH c .

Gilbert's damping constants, α , of Co( t Co )/Pt (1.4 nm) multilayer thin films are investigated by Q-band FMR analysis. α is calculated from the resonance width of the FMR spectrum. With decreasing t Co , the α value decreases from 0.034 ( t Co =8.7 nm) to 0.023 ( t Co =1.8 nm), and then increases to 0.037 ( t Co =1.0 nm). The decrease of α with t Co >1.8 nm is probably due to the eddy current loss effects. The increase of α with t Co θ =90° (parallel to the specimen) to θ =0° (perpendicular to the specimen), the α of all the specimens increased, and a sharp step in α was observed around θ =40°, where the α has the maximum value.

Effects of Fe and Co addition on the magnetoresistance MR were investigated in sputtered Ni-Mn-Ga-M (M = Fe, Co) films. With increasing M content, magnetization σ enhanced for M = Fe, while it reduced for M = Co. At 300 K, absolute MR value at 1.5 T |MR|1.5 was about 1%. The value of |MR|1.5 was found to be decreased with increasing M = Fe content. In the case of M = Co, |MR|1.5 increased with M content. |MR|1.5 of the film containing Co 1.6 at.% showed a maximum value of 2.5% at 355 K in the vicinity of the Curie temperature TC. An origin of MR behavior in the present films was suggested to be explained by a s-d scattering model.

The effects of Nd2Fe14B grain size and Nd coating on the coercivity in sputter-deposited Nd-Fe-B/Nd thin films have been investigated in order to gain an insight into the coercivity mechanism of Nd-Fe-B magnets. Highly textured Nd2Fe14B particles were grown successfully on the MgO(100) single-crystal substrate with the Mo underlayer. As the Nd-Fe-B layer thickness t NFB was decreased from 70 to 5 nm, the coercivity H c increased gradually from 6.5 to 16 kOe. By depositing the Nd overlayer onto these films and post-annealing at 500 °C, the H c value further increased from 17.5 kOe (t NFB=70 nm) to 26.2 kOe (t NFB=5 nm). The amount of H c increase by the combination of the Nd coating and post-annealing was about 10 kOe irrespective of the t NFB value. These results therefore suggest an independence of size and interface effects on the coercivity of Nd-Fe-B magnets.

The ceramic pellets of the nominal compositions Bi$_{0.7}$Ba$_{0.3}$Fe$_{1-x}$Ti$_x$O$_3$ (x = 0.00-0.20) were prepared initially by standard solid state reaction technique. The pellets were then ground into micrometer-sized powders and mixed with isopropanol in an ultrasonic bath to prepare nanoparticles. The X-ray diffraction patterns demonstrate the presence of a significant number of impurity phases in bulk powder materials. Interestingly, these secondary phases were completely removed due to the sonication of these bulk powder materials for 60 minutes. The field and temperature dependent magnetization measurements exhibited significant difference between the magnetic properties of the bulk materials and their corresponding nanoparticles. We anticipate that the large difference in the magnetic behavior may be associated with the presence and absence of secondary impurity phases in the bulk materials and their corresponding nanoparticles, respectively. The leakage current density of the bulk materials was also found to suppress in the ultrasonically prepared nanoparticles compared to that of bulk counterparts., Comment: 9 pages in Journal of Physics D: Applied Physics, 2016

We investigated the dependence of magnetic properties for Co/Pt100–xPdx multilayer thin films on the concentration in the Pt-Pd alloy layers. Perpendicular magneto anisotropy constant Kp increases with increasing Pt concentration in the Pt-Pd layer, since the interface anisotropy between the Co and the Pt-Pd layers is enhanced by the increase of the Pt concentration. The Curie temperature and the temperature dependence of Kp for the specimens increase with increasing the amount of Pt in the Pt-Pd layer. These results may indicate that the lattice distortion of the Co layer caused by the interface from the Pt-Pd layer becomes larger and the increase of the distortion enhances the interface anisotropy, since the lattice misfit between the Pt-Pd and the Co increases with increasing the Pt concentration. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

We investigated La-coated Nd2Fe14B thin film magnets by scanning/transmission electron microscopy to clarify the coercivity enhancement mechanism in Nd-Fe-B permanent magnets. The coercivity of La-coated film magnets was increased from 8.5 to 15 kOe by post-annealing. The fcc-LaOx layer was epitaxially grown on [001]-oriented Nd2Fe14B fine grains with a crystallographic orientation relation of Nd2Fe14B (001)[110] || LaOx (111)[112¯], both in the as-deposited and post-annealed films. STEM-EDS elemental analysis revealed that the only difference caused by post-annealing was the O content in the LaOx layer, which increased from 15 to 35 at.%. These results suggest that the magnetocrystalline anisotropy of the Nd ions, which were reduced at the surface of Nd2Fe14B, would be recovered by the presence of O, leading to a remarkable increase in the coercivity.

The inference of a magnetic field on the martensitic transformation (MT) temperatures and shape memory effect (SME) was investigated for the Ni-rich Ni 2 MnGa sputtered films. The compositions of the films were Ni 51.4 Mn 28.3 Ga 20.3 , Ni 54.1 Mn 23.0 Ga 22.9 and Ni 54.4 Mn 21.3 Ga 24.3 . The films were heat treated at 1073 K for 3.6 ks and aged at 673 K for 3.6 ks in a constrained condition. Hereafter, the constraint-aged films were described as N51.4(AG), N54.1(AG) and N54.4(AG) using nickel content, respectively. The reversible two-way SME by the thermal change was confirmed for the all constraint-aged films through the MT and its reversion. The gradient of the strain–temperature curve, the amount of strain accompanied by the two-way SME and the width of thermal hysteresis were dependent on the composition of the films. The strain–temperature curves shifted to a high temperature region and the martensitic phase was stabilized by the magnetic field. The strain at the outer surface was given by e = d /2 r , where d was the thickness of the films and r was the radius of a curvature for the films. The increase of MT temperatures caused by a magnetic field was about 1 K/T. Furthermore, the two-way SME by the magnetic field was observed around the MT temperature on cooling for the N54.4(AG) film with the large gradient and small thermal hysteresis in the strain–temperature curve.

Magnetoresistance (MR) of Ni–Mn–Ga–Fe shape memory films was investigated. The films with different Fe composition were prepared by co-sputtering method. The obtained films were heat-treated at 1073 K for 1 h in a flow of Ar gas. MR was measured by four point probe method at constant temperature by changing magnetic field up to ± 15 kOe . With increasing Fe composition, Curie temperature T c and saturation magnetization M s increased and martensitic transformation temperatures decreased. Negative and isotropic MR was found. MR at the magnetic field of 15 kOe increased with increasing temperature. MR of the film without Fe composition was - 0.44 % at 77 K and - 2.19 % at 353 K in martensitic phase. MR of the film containing 6.1 mol% Fe was - 0.30 % at 77 K in martensite phase and - 0.89 % at 353 K in austenitic phase. MR decreased with the increasing Fe composition. The MR of the films at R.T. below T c was larger than that at 77K. This temperature dependency of the MR suggest that negative MR of the constraint-aged Ni–Mn–Ga–Fe films is attributed to the s conduction electron scattering by the localized d spins in the modified s–d scattering model.

Gilbert's damping constants, alpha, of Ni-Fe and Ni-Co thin films are determined by Q-band ferromagnetic resonance (FMR) analysis. alpha is calculated from the resonance width of the FMR spectrum. alpha of Ni85 Fe15 film is found to be 0.0034, which is one-fourth of those of Ni film (alpha=0.013) and Co (alpha=0.013). alpha of the Ni100-x Cox specimens increases with decreasing the Co concentration from 100 to 68 at%, and the alpha value of Ni32 Co68 film has the maximum value of 0.0021. The alpha values of the Ni-Co specimens are nearly the same as those of the Co-Cr-Ta and the Co-Cr-Pt

Low surface resistance is achieved by introducing BaZrO3 nano-particles in high crystalline quality ErBa2Cu3O7-δ films. The surface resistance of a ErBa2Cu3O7-δ film with BaZrO3 nano-particles grown by pulsed laser deposition is 55% of that without BaZrO3 nano-particles near 65 K. This result suggests that the ErBa2Cu3O7-δ films with BaZrO3 nano-particles have potential as high power microwave emitting devices. A new direction is shown for reducing the surface resistance of superconducting films.

Effect of adding cobalt on the shape memory properties of Ni-Mn-Ga sputtered films was investigated. It was found that the films containing cobalt less than 5.1 mol% has a single phase and those with more than 6.8 mol%Co has two phases. The Curie temperature increased and the saturation magnetization decreased with increasing cobalt content. These films exhibited one way shape memory effect. The shape recovery start temperature increased and the temperature range of shape change broadened with increasing cobalt content.

A model sample with an interface of the Nd2Fe14B(100) plane and the α-Fe phase was fabricated in order to evaluate the exchange-coupling constant Jex between these two ferromagnetic phases. By measuring the ferromagnetic resonance fields and the Kerr loops, the Jex was confirmed to be negative with the value of Jex = −6.5 × 10−4 J/m2, in striking contrast to the positive Jex value for the Nd2Fe14B(001)/α-Fe(100) interface reported previously.

The electrical resistivity and magnetization as a function of temperature have been investigated for Cr 2 Se 3 and its Te-substitution system. The temperature dependence of electrical resistivity for Cr 2 Se 3 shows a metallic behavior above T N . That of Cr 2 Se 2.8 Te 0.2 shows a semiconductor-like behavior. The temperature dependence of magnetization of Cr 2 Se 2.8 Te 0.2 shows a canted antiferromagnet-like behavior.

Nd2Fe14B films with the c-axis perpendicular to the film plane were deposited by introducing Mo (110) underlayer on the SiO2 substrates. When the temperature of the substrate during the deposition of the Nd-Fe-B layer was 600 °C, the demagnetization curve exhibited the coercivity of Hc=11 kOe. We observed an Hc increase of up to 14 kOe by capping the film with the Nd overlayer and post-annealing at 500°C. Cross-sectional TEM observation and NBD analysis suggest that the Nd in the overlayer is in the oxide state with either cubic-NdO2 or hcp-Nd2O3 structures.

Change in magnetization and electrical resistivity by annealing was examined for cold rolled Fe 47 Rh 53 alloy. The temperature hysteresis of magnetization was observed for the ferromagnetic phase. The resistivity increased with annealing time at 870 K. These results are discussed in relation to inhomogeneous magnetic and atomic structures.