Tetsuroh Kawai

Magnetostrictive Behavior of Fe–Si Single-Crystal Films With Different Orientations Under Rotating Magnetic Fields

Magnetostrictive behaviors of Fe-Si single-crystal hlms are investigated under rotating magnetic helds up to 1.2 kOe. The output waveform of (001) film is triangular, and that of (110) film is bathtub-like, while a (111) film shows very small variation with respect to the angle of the applied magnetic held. The waveforms are different from ideal sinusoidal waveforms. The results indicate that magnetocrystalline anisotropy is playing an important role on the magnetostrictive behavior. The (001) film shows a typical fourfold anisotropy and the (110) film shows uniaxial-like anisotropy. Considering the magnetocrystalline anisotropy, the complex magnetostrictive behavior can be analyzed by employing a 90° domain wall motion model or a coherent rotation model. The small magnetostrictive behavior of (111) film is due to the opposite signs of λ100 and λ111.

Relationship Between Magnetostriction and Magnetic Domain Structure in Fe-Based Alloy Single-Crystal Films With bcc(001) Orientation

Fe, Fe₉₄Si₆, Fe₉₈C₂, and Fe₉₅B₅ (at. %) single-crystal thin films of bcc(001) orientation are prepared on MgO(001) substrates using an ultrahigh-vacuum magnetron sputtering system. The influence of magnetic anisotropy on the magnetostriction under rotating magnetic field is investigated. Fe, Fe₉₄Si₆, and Fe₉₈C₂ films show four-fold symmetries in in-plane magnetic anisotropy, where easy and hard magnetization directions are, respectively, observed along bcc[100] and bcc[110]. Higher saturation fields measured along bcc[110] are recognized in the order of Fe (6 kOe) > Fe₉₈C₂ (5 kOe) > Fe₉₄Si₆ (4 kOe). Triangle output waveforms of magnetostriction appear when these films are measured under low-rotating fields. The behavior is related with the motion of 90° magnetic domain walls in magnetically unsaturated film. With increasing the rotating field, the films approach to magnetic saturations and the waveform gradually shifts to usual sinusoidal shape. Larger threshold rotating field is observed in the order of Fe > Fe₉₈C₂ > Fe₉₄Si₆, which is related to the saturation field. On the contrary, Fe₉₅B₅ film possesses an almost isotropic property in in-plane measurement and shows sinusoidal waveforms even when the film is magnetically unsaturated. The waveform is affected by the symmetry and the strength of magnetic anisotropy.

Magnetostrictive behaviors of Fe-Si(001) single-crystal films under rotating magnetic fields

Magnetostrictive behaviors under rotating magnetic fields are investigated for bcc(001) single-crystal films of Fe100−x-Six(x = 0, 6, 10 at. %). The magnetostriction observation directions are along bcc[100] and bcc[110] of the films. The magnetostriction waveform varies greatly depending on the observation direction. For the observation along [100], the magnetostriction waveform of all the films is bathtub-like and the amplitude stays at almost constant even when the magnetic field is increased up to the anisotropy field. On the other hand, the waveform along [110] is triangular and the amplitude increases with increasing magnetic field up to the anisotropy field and then saturates. In addition, the waveform of Fe90Si10 film is distorted triangular when the applied magnetic fields are less than its anisotropy field. These magnetostrictive behaviors under rotating magnetic fields are well explained by employing a proposed modified coherent rotation model where the anisotropy field and the magnetization re...

Thickness Effect on Magnetostriction of Fe and Fe

Film thickness effect on saturation magnetostriction of Fe and Fe98B2 thin films has been investigated in relation to the film strain. Saturation magnetostriction varies from -4 × 10-6 to +3 × 10-6 with decreasing the film thickness from 40 to 10 nm, changing the sign at around 15 nm for both the Fe and the Fe98B2 films. The saturation magnetostrictions of Fe98B2 films of 7 and 5 nm thicknesses are +10 × 10-6 and +17 × 10-6, respectively. XRD patterns observed for these films show only the bcc(110) reflection, which indicates that the films consist of oriented nanocrystals with bcc structure. The lattice spacing, dbcc(110); increases with decreasing the film thickness from 20 to 10 nm for both Alms. With decreasing the film thicknesses, both magnetostriction and strain increase. These experimental results support the theoretical study which suggests a strain effect on magnetostriction.

_{98}

Magnetostrictive behaviors of Fe_100-xB_x(001), x = 0, 5, and 13 at. %, single-crystal films are studied in comparison with those of poly-crystal Fe-B films under rotating magnetic fields. The output waveform of poly-crystal Fe-B film is sinusoidal and the saturation magnetostriction, λ_s, varies from negative to positive with increasing the B composition, x, from 0 to 13 at. %. On the other hand, the output waveform of single-crystal Fe-B film is bathtub-like when measured along the easy magnetization axis of bcc[100], while it changes to triangular when measured along the hard magnetization axis of bcc[110]. The output waveform is strongly influenced by the magnetocrystalline anisotropy under a magnetic held of 1 kOe which is larger than the anisotropy held of the material. Variations of λ₁₀₀ and λ₁₁₁ values are estimated as a function of B content. λ₁₀₀ of Fe-B hlm shows a positive value and increases with increasing the B content from 0 to 13 at. %, while the value of λ₁₁₁ changes from negative to positive with increasing the B concentration. The B content dependence of λ_s for poly-crystalline Fe-B samples is explained by considering the B content dependence of λ₁₀₀ and λ₁₁₁ determined with single-crystal film samples.

B

A broadband inductive technique has been applied to measure static magnetic field dependence of resonant frequency for Fe(001) and Fe-Co(001) single-crystal thin films. Different dependences of resonant frequency are observed depending on the static magnetic field application direction between [100] and [110]. The phenomenon is analyzed using the Kittels resonance formula. The calculated values obtained by using three fitting parameters of saturation magnetization, Ms, anisotropic energy, K1, and g-factor show good agreements with the experiments for both crystal orientations of [100](easy axis) and [110](hard axis) for Fe(001) single-crystal thin film. The three fitting values are close to those of bulk single-crystal Fe. There is a discrepancy between experiment and calculation for the hard axis, [100], of Fe-Co single-crystal film. It is considered that magnetoelastic energy originating from large positive magnetostriction has some effect on the phenomenon observed for Fe-Co(001) thin films when measured along the hard magnetization axis.

_{2}

Fe100–xAlx (x = 0, 4, 10, 20, 30 at. %) alloy films of 40 nm thickness are prepared on MgO(001) single-crystal substrates by varying substrate temperature from room temperature to 600 °C. Single-crystal films of (001) orientation with bcc-based disordered A2 structure are obtained for the Al content range of x = 0 - 20 at. %. An ordered phase of DO3 structure is observed in Fe70Al30 films prepared at temperatures higher than 200 °C, whereas (001) oriented single-crystal films of A2 structure are obtained when prepared at room temperature. The film surface profile does not depend much on the film composition, while the surface roughness increases with increasing substrate temperature. Island-like crystals are observed for films prepared at 600°C for all compositions. Difference in lattice spacing measured parallel and perpendicular to the substrate is noted for the single-crystal thin films and it increases with increasing Al content. The lattice strain in single-crystal film is caused possibly to accommod...

Thin Films

Soft magnetic materials have been widely used for applications like transformers, motors, and magnetic devices, where the materials are often exposed to alternating magnetic fields.