Induced In-plane Uniaxial Anisotropy Research Articles

Tunable magnetization dynamics in disordered FePdPt ternary alloys: Effects of spin orbit coupling

The magnetization dynamics of disordered Fe0.5(Pd1−xPtx)0.5 alloy films was studied by time-resolved magneto-optical Kerr effect and ferromagnetic resonance. The intrinsic Gilbert damping parameter α0 and the resonance linewidth change linearly with the Pt atomic concentration. In particular, the induced in-plane uniaxial anisotropy constant KU also increases for x increasing from 0 to 1. All these results can be attributed to the tuning effect of the spin orbit coupling. For the disordered ternary alloys, an approach is proposed to control the induced in-plane uniaxial anisotropy, different from conventional thermal treat methods, which is helpful to design and fabrications of spintronic devices.

Magnetization reversal of Tb-Co/Fe19Ni81 films with a unidirectional anisotropy

Conditions have been found for the realization of induced in-plane uniaxial anisotropy of the amorphous Tb31Co69 films and of unidirectional anisotropy in the Permalloy layers in the composite two-layered Tb31Co69/Fe19Ni81 films. The mechanisms of magnetization reversal in such film structures have been studied in a temperature range of 5–300 K. It has been found that a decrease in temperature leads to a transformation of hysteresis loops, a significant increase in the field of unidirectional anisotropy, and a nonmonotonic change in the coercive force of the Permalloy layer. The regularities found are interpreted taking into account the variation in the properties of the amorphous layer Tb31Co69 with temperature under the assumption on a temperature-induced change in the localization of the interlayer magnetic boundary, which is formed upon a layer-by-layer magnetization reversal of the film structure.

Influence of Si concentration on the magnetization dynamics in as-sputtered FeCoSiN thin films at high frequencies

In this work, the high-frequency magnetic permeability spectra of as-sputtered FeCoSiN films with various Si concentrations were investigated. The soft magnetic properties with an induced in-plane uniaxial anisotropy can only be obtained within some composition ranges because of the formation of different granular microstructures. The permeability spectra measured without any external fields (He) were well fitted based on the phenomenological Landau–Lifshitz–Gilbert equation. Results show that with the increase in Si concentration, the saturated magnetization 4πMs, the resonance frequency fr, the permeability μ, and the qualify factor Q values decrease, while the damping coefficient α and resonant frequency linewidth Δf increase. The increase in Gilbert damping coefficient α or G is ascribed to the increase in mosaicity or magnetic ripples with higher volume proportion of Si-rich matrix. The investigations on Δf-He relations indicate the extrinsic damping contribution from the two-magnon scattering in FeCoSiN, which is suggested to be due to the change in the granular microstructures compared with FeCoN.

An approach for researching uniaxial anisotropy magnet: Rotational magnetization

In this study, rotational magnetization curves are used to investigate the anisotropy and the rotational magnetization process of uniaxial magnets. We measured the projection of magnetization as a function of angle between the magnetic field and the reference axis. The information about anisotropy, such as the directions of the easy axis and hard axis, as well as the anisotropy field Hk(i), is acquired. Simultaneously, the rotational magnetization reversal processes are derived. The Co and Fe28Co61Zr11 magnetic thin films with induced in-plane uniaxial anisotropy have been researched. We found that the rotational magnetization reversal process of the Co film is a coherent rotation. However, the Fe28Co61Zr11 film shows the similar behavior, except for a noncoherent rotation appearing when a small field parallels the hard axis.

Ferromagnetic resonance studies on (Co 40Fe 40B 20) x(SiO 2) 1−x granular magnetic films

Magnetic properties of granular (Co 40Fe 40B 20) x (SiO 2) 1− x thin films ( x = 0.3 7 - 0.5 3 ) have been studied by ferromagnetic resonance (FMR) technique. Samples have been prepared by ion-beam deposition of Co–Fe–B particles and SiO 2 on sitall ceramic substrate. The FMR measurements have been done for different orientations of DC magnetic field with respect to the sample plane. It was found that the deduced value of effective magnetization from FMR data of the thin granular film is reduced by the volume-filling factor of the bulk saturation magnetization. The overall magnetization changes from 152 to 515 G depending on the ratio of the magnetic nanoparticles in the SiO 2 matrix. From angular measurements an induced in-plane uniaxial anisotropy has been obtained due to the preparation of the film conditions as well.

Soft/hard exchange-coupled layered structures with modulated exchange coupling

Magnetically soft/hard exchange-coupled Ni80Fe20/Si3N4/Sm40Fe60 and Ni80Fe20/mixture/Sm40Fe60 layered structures with induced in-plane uniaxial anisotropy were deposited by sputtering on Si (100) substrates. The interfacial exchange coupling strength between the soft and hard layers was tailored by inserting a thin nonmagnetic insulating Si3N4 layer or by varying interfacial mixture of NiFe and SmFe. It was found that the reduction in the exchange coupling greatly reduces the nucleation field HN of the soft layer and increases the irreversible switching field Hirr of the hard layer. The simple formula used before to describe the nucleation field of the soft layer does not work in the case of the reduced interfacial exchange coupling.

Critical dimension of the transition from single switching to an exchange spring process in hard/soft exchange-coupled bilayers

Hard/soft exchange-coupled ${\mathrm{Ni}}_{80}{\mathrm{Fe}}_{20}/{\mathrm{Sm}}_{40}{\mathrm{Fe}}_{60}$ bilayers with well-defined induced in-plane uniaxial anisotropy were deposited on (100) Si and glass substrates by dc magnetron sputtering. The magnetization-reversal process was systematically studied by analyzing the magnetic hysteresis loops measured by the alternating-gradient magnetometer and surface-sensitive magneto-optic Kerr effect. The coercivity in the single-switching process and the nucleation field in the exchange spring process are quantitatively described by theoretical models. As a result, a critical dimension equation describing the transition from a single-switching process to an exchange spring process is developed. Different magnetization-reversal processes are essentially determined by the exchange length (or domain wall width) of the soft layer under an external field and the pinning energy exerted on the domain wall of the hard layer near the interface.

Modulated magnetic properties of hard/soft exchange-coupled SmFe/NiFe multilayers

Very well-defined induced in-plane uniaxial anisotropy, not obtainable in single layer SmFe films, has been observed in Sm 40Fe 60/Ni 80Fe 20 multilayers. The easy axis coercivity monotonically decreases as the thickness of NiFe (SmFe) layers increases (decreases). These experimental results are well described theoretically by an extended domain wall unpinning model. The easy axis coercivity and the hard axis saturation field can be reduced by appropriate annealing procedures. Moreover, for multilayers with well-defined uniaxial anisotropy, a linear relationship between the easy axis coercivity and the hard axis saturation field is found, no matter whether the change in coercivity and saturation field is caused by a change in thickness or by annealing. Finally, the evolution in structure caused by annealing is studied by X-ray diffraction and correlated with changes in the coercivity and saturation field. The ability to tailor the magnetic behavior of such systems is critical to optimizing the performance of multilayered giant magnetostrictive films.

Anomalous magnetization processes in the amorphous compensated Tb 21Co 79 alloy

Magnetic properties of amorphous Tb x Co 100- x alloys with an induced in-plane uniaxial anisotropy were studied. Complex reorientation transitions, not observed earlier in amorphous materials, were found. These transitions were most vivid in Tb 21Co 79 amorphous alloy, in which at low temperatures the resulting moments of Tb and Co sublattices practically compensate one another.

Study of induced uniaxial anisotropy in magnetic thin films by transverse susceptibility

The transverse susceptibility was measured in Co86Ti14 ferromagnetic thin films which possess an induced in-plane uniaxial anisotropy, as a function of a dc magnetic field H applied parallel to the hard axis. The susceptibility reaches a sharp maximum when H is close to the value of the anisotropy field HK previously determined. A theoretical model based upon a small deviation of H from the hard axis is developed to evaluate the angular dispersion of HK.

Enhancement of the nuclear signal in magnetic thin films with induced uniaxial anisotropy

59Co NMR studies of Co86Ti14 soft ferromagnetic amorphous thin films that possess an induced in-plane uniaxial anisotropy have been performed at 4.2 K. The spin-echo amplitude has been measured as a function of a DC magnetic field H applied in the film plane along the easy and hard axes. The field dependence of the signal intensity is quite consistent with the calculated enhancement factor. The signals observed in zero external field with a RF field applied along the easy and hard axes show that the enhancement mechanism does indeed arise from domain rotation and the deviation of the magnetisation direction from the easy axis is small.

Evidence for structure-related induced anisotropy in amorphous CoTi soft ferromagnetic thin films.

When amorphous ${\mathrm{Co}}_{1\ensuremath{-}x}{\mathrm{Ti}}_{x}$ soft ferromagnetic thin films are deposited by rf sputtering in the presence of a dc magnetic field one observes a somewhat bell-shaped variation of the induced in-plane uniaxial anisotropy energy ${K}_{u}$ as a function of the pressure of the sputtering gas ${P}_{\mathrm{Ar}}$. The maximum value of ${K}_{u}(x)$, ${[{K}_{u}(x)]}_{max}$, is obtained for the same ${P}_{\mathrm{Ar}}$ for the whole concentration range studied $0.14\ensuremath{\le}x\ensuremath{\le}0.22$. The origin and the overall variations of ${K}_{u}$ are interpreted for the first time in terms of the atomic local anisotropies. The continuous decrease of ${({K}_{u})}_{max}$ with increasing Ti concentration is explained by the progressive change of the local structure.