Amorphous TbFe Films Research Articles

Strain-induced magnetic domain wall control by voltage in hybrid piezoelectric BaTiO3 ferrimagnetic TbFe structures.

This paper reports on the voltage dependence of the magnetization reversal of a thin amorphous ferromagnetic TbFe film grown on a ferroelectric and piezoelectric BaTiO3 single crystal. Magneto-optical measurements, at macroscopic scale or in a microscope, demonstrate how the ferroelectric BaTiO3 polarisation history influences the properties of the perpendicularly magnetized TbFe film. Unpolarised and twinned regions are obtained when the sample is zero voltage cooled whereas flat and saturated regions are obtained when the sample is voltage cooled through the ferroelectric ordering temperature of the BaTiO3 crystal, as supported by atomic force microscopy experiments. The two steps involved in the TbFe magnetization reversal, namely nucleation and propagation of magnetic domain walls, depend on the polarisation history. Nucleation is associated to coupling through strains with the piezoelectric BaTiO3 crystal and propagation to pinning with the ferroelastic surface patterns visible in the BaTiO3 topography.

Improvement of diffraction efficiency of three-dimensional magneto-optic spatial light modulator with magnetophotonic crystal

We have developed three-dimensional magneto-optic spatial light modulators (3D-MOSLMs) that use magnetic domains as submicron scale pixels to represent holograms. Our display system uses a submicron-scale magnetic pixel array on an amorphous TbFe film to create a wide viewing angle hologram. However, in previous work the reconstructed images had a low intensity and a low optical contrast; brightness of the reconstructed image was 4.4 × 10−2 cd/m2 with 532 nm illumination light at 10.8 mW/cm2, while display standard ISO13406 recommends 100 cd/m2 or more. In this paper, we describe our development of a 3D-MOSLM composed of an artificial magnetic lattice structure of magnetophotonic crystals (MPCs). The MPCs enhance the diffraction efficiency of reconstructed 3D images and reduce the power consumption for controlling the magnetic pixels by a light localization effect. We demonstrate reconstructed 3D images using the MPC and show significant brightness improvement.

Magneto-optic spatial light modulator with submicron-size magnetic pixels for wide-viewing-angle holographic displays.

Spatial light modulators (SLMs) with submicron-size pixels are promising devices for use in wide-viewing-angle glasses-free holographic 3D displays. In accordance with estimations, an SLM with 1μm pitch pixels can display holographic images over viewing angles of 30deg. In the present work, we have studied magneto-optic SLMs (MOSLMs) with submicron-size pixels for wide-viewing-angle holographic displays that are driven by thermomagnetic recording. Amorphous TbFe films were used as a magneto-optic material. The MOSLM with an 800nm diameter pixels array displayed wide-viewing-angle holographic images. These results demonstrated that MOSLMs with submicron-size pixels have promise for glasses-free holographic 3D displays.

Morphogenesis of maze-like magnetic domains

The present study explains the morphogenesis of maze-like magnetic domains in amorphous Tb-Fe films. It is shown that the observed morphological complexity of the maze-like patterns (which arise due to out-of-plane anisotropy) is superficial and can be explained by simple geometrical rules based on magnetostatic interactions between domains. Morphogenesis in applied field occurs in a fractal-like manner through growth of self-similar reversed domains of various shapes at progressively smaller length scales; the field-dependent fractal dimensions are quantified. The microscopic changes in domain morphology manifest as distinct kinks or ``knees'' in the macroscopic magnetization curves. Highly aligned synthetic patterns can be formed in microfabricated films, illustrating the potential for ``domain engineering'' for controlled magnetoelastic response.

Effects of argon pressure on magnetic properties and low-field magnetostriction of amorphous TbFe films

Amorphous TbFe films were fabricated by DC magnetron sputtering, and the effects of argon pressures on the microstructure, magnetic properties and the low magnetic field magnetostrictions of the samples were explored. It is found that with the increase of argon pressure, the surface smoothness and the compactness of TbFe films are declined. At lower argon pressure, maze magnetic domains exist, and it possesses, hence, stronger perpendicular anisotropy. With the increase in argon pressure, the domain walls become gradually wider and the contrast of domain image appears to be less sharper. It implies that the magnetic anisotropy direction of the films gradually changes from perpendicular to parallel to the film plane with larger argon pressure. In addition, the magnetization is stronger with increase in argon pressure, and reaches its maximum value at 0.6 Pa. After that, the magnetization begins to decrease with further increase in argon pressure. However, the coercivity of the films decreases monotonically with the increase in the argon pressure. At low magnetic fields, the magnetostriction of amorphous TbFe films becomes larger with increase in the argon pressure. After reaching its maximum value at 0.6 Pa, a decrease was observed with further increase in argon pressure.

Composition-Controlled Low Field Magnetostriction of TbFe Amorphous Films

Amorphous TbFe films are fabricated by dc magnetron sputtering, and their magnetostrictions at low field are examined over a wide range of terbium content (from 32 at.% to 70 at.%). It is found that the terbium content plays an important role in the magnetic and magnetostrictive properties of TbFe films. TbFe film soft magnetic properties and low field magnetostriction can be efficiently improved by controlling the terbium at an optimum content. The magnetostriction at lower magnetic field is increased with the increase of terbium content up to 48.2 at.%. After reaching the maximum value, further increase of terbium content would result in a great decrease of the low field magnetostriction. By contrast, at higher magnetic field, the magnetostriction is decreased monotonically with the increase of the terbium content.

Selective-resputtering-induced perpendicular magnetic anisotropy in amorphous TbFe films.

Perpendicular magnetic anisotropy energy in rf magnetron sputtered amorphous TbFe films is measured to increase exponentially with pair-order anisotropy induced by the selective resputtering of surface adatoms during film growth.

Evidence for selective resputtering as the growth mechanism of pair-order anisotropy in amorphous TbFe films

Processing conditions for rf magnetron sputter-deposited amorphous TbFe films in which an atomic scale structural anisotropy (ASSA) results as a natural consequence of selective resputtering at the film surface during growth are presented. The ASSA, measured using polarization-dependent X-ray absorption fine structure with quantitative modelling via a parametrized nonlinear least squares fitting, is described as a pair order anisotropy (POA) where a statistical preference exists for like atom pairs in-plane and unlike atom pairs perpendicular to the film plane. The perpendicular magnetic anisotropy (PMA) energy increases with increasing POA for samples grown using decreasing rf power and increasing working gas pressure. The POA directly reflects the anisotropic electrostatic environment at the rare earth site which is required for PMA to result from a single ion anisotropy mechanism.

Magnetic interactions and anisotropy in amorphous TbFe films

This work examines one of the more important properties of amorphous TbFe thin films: the perpendicular magnetic anisotropy. A series of structural and magnetoelastic measurements is presented, indicating the existence of a bond order anisotropy related to the magnetic anisotropy. Finally, in order to account for both the perpendicular anisotropy and the positive magnetostriction, we propose a model of anisotropy based on the observed bond distribution.

Improvement of low field magnetostriction of amorphous TbFe sputtered films by thermal annealing

To improve the low field magnetostrictive response of TbFe sputtered films, the effects of slow rate and rapid rate thermal annealing on the magnetic and magnetoelastic properties of the films were investigated. The annealing was achieved for amorphous TbFe films with the composition around 40 at.% Tb, because these films simultaneously exhibit relatively soft inplane magnetization and considerably large magnetostriction. The present work shows that thermal annealing is very effective for improving the low field magnetostrictive response of a film, for example, the engineering magnetostriction of amorphous Tb/sub 40/Fe/sub 60/ film at 500 Oe became 5.1 times larger by annealing from 46/spl times/10/sup -6/ to 235/spl times/10/sup -6/.

57Fe hyperfine field distribution for TbFe thin films and multilayers

57Fe Mössbauer spectra in amorphous Tb x Fe 1- x films (AF) and Tb/Fe multilayers (MLs) were measured for a wide range of concentration and layer thicknesses. A small angle between the film normal and direction of H hf was observed. This effect and the concentration dependence of 57Fe hyperfine field in amorphous TbFe films are discussed.

Magnetostriction in TbDyFe thin films

Magnetization and magnetostriction in amorphous binary TbFe and DyFe and amorphous and polycrystalline, ternary (TbxDy1−x)yFe100−y thin films have been investigated. The measurements reflect the compositional dependence of the easy direction of magnetization in the films. In plane magnetostrictions of over 300×10−6 were measured for some of the amorphous TbFe and TbDyFe films and values greater than 750×10−6 were obtained in polycrystalline TbDyFe films near to the Terfenol composition.

Unidirectional magnetic anisotropy in amorphous Tb-Fe films

The torque curves (TC) of amorphous TbFe films with the thicknesses d=40-80 nm and compositions near room temperature compensation point were experimentally investigated. The films were evaporated by the electron-beam method. Unidirectional (exchange) anisotropy revealed in TC hysteresis is detected and explained by the strong chemical inhomogeneities of the films. The Fe inclusions are the characteristic peculiarity of Tb-Fe films. Their dimensions are determined by the preparation technique. The exchange field on Tb ions is estimated by using the temperature dependence of the TC amplitude as 1.1-1.3/spl middot/10/sup 6/ Oe. >

Magnetic and Magnetoelastic Properties of Highly Magnetostrictive Amorphous Films with TbFe-FeB-TbFe Sandwich Structure

AbstractAmorphous Tb40Fe60-Fe80B20-Tb40Fe60 sandwich films were prepared by multitarget rf magnetron co-sputtering. Their magnetization and magnetostriction were studied to examine whether magnetic softening of the amorphous TbFe films could be achieved without loosing their giant magnetostriction by introducing the simple sandwich structure. The results revealed that a considerably soft in-plane magnetization (coercive force H≈ 6Oe and the squareness ratio Mr/Ms≈ 0.8) and a huge magnetostriction (λ >500ppm) could be obtained in the sandwich films at room temperature, provided that the thickness of the FeB interlayer was within the range of 10% to 40% of the total film thickness (1 μm).

Tb-Fe Sputtered Films with Large Magnetostriction for Use in Magnetomechanical Thin-Film Devices

We examined the magnetostriction and coercive force of amorphous Tb-Fe films sputter-deposited under different conditions (rf input power, Ar gas pressure, Tb content, etc.). Here we discuss the possibility of obtaining both soft magnetic properties and a large magnetostriction in this system. Soft magnetic properties and large magnetostriction were obtained simultaneously in sputtered Tb-Fe thin films prepared with a Tb content of 45 to 50 at%, under an Ar gas pressure of 4 mTorr and with an rf input power of 200 W. This material has strong potential for use in magnetomechanical thin-film devices.

Domain wall motion in RE-TM films with different thickness

A thermally activated domain wall motion is studied in amorphous TbFe films with different thicknesses. The activation energy of the domain wall displacement process is determined for the films with various composition and thicknesses. It is about 2.5 eV. The activation volume of this process nonlinearly increases from 2*10/sup -18/ cm/sup 3/ to 7*10/sup -18/ cm/sup 3/ as the film thickness increases from 25 nm to 400 nm. The change of the domain shape with the film thickness growth and domain wall coercive force dependence on film thickness are discussed in terms of thermoactivated domain wall motion.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Substrate temperature effect on the structural anisotropy in amorphous Tb–Fe films

Using extended x-ray absorption fine structures (EXAFS) measurements we have investigated the atomic environment around the Fe atom in a series of amorphous Tb0.26Fe0.74 films having different magnetic anisotropy energies owing to different deposition temperatures. The polarization properties of synchrotron radiation allowed the separate study of structure parallel and perpendicular to the sample plane. An anisotropy between these two structures was observed. Modeling results indicate this anisotropy is due to anisotropic pair correlations where the Fe–Fe pairs are statistically preferred in-plane and the Fe–Tb pairs out-of-plane. The amplitude of this anisotropy scales with both the substrate temperature and the magnetic anisotropy energy. A ≊1% in-plane compression of the Fe–Fe distance was measured between the in-plane and out-of-plane structure of the sample grown at 77 K. This sample had no detectable local chemical anisotropy suggesting that intrinsic stress plays an important role in determining its magnetic anisotropy.

CORRELATION OF MAGNETIC AND STRUCTURAL ANISOTROPY IN AMORPHOUS TB-FE VIA EXAFS

Using extended x-ray absorption fine structure (EXAFS) we have measured a structural anisotropy between the in-plane and out-of-plane structure in amorphous Tb-Fe films. This anisotropy is manifested as a statistical preferrence for like pairs to orient in-plane and unlike pairs out-of-plane. The magnitude of this anisotropy correlates with the measured magnetic anisotropy energy as a function of the alloy composition, heat treatment, and substrate temperature. We present here details of the EXAFS data collection, analysis and modeling.

電気機械変換薄膜素子用Ｔｂ‐Ｆｅスパッタ薄膜の磁歪

We examined the magnetostriction and coercive force of amorphous Tb-Fe films while varying the sputtering conditions (rf input power, Ar gas pressure, Tb content, and so on). Here we discuss the possibility of obtaining both soft magnetic properties and large magnetostrictionin this system. Soft magnetic properties and large magnetostriction were obtained simultaneously in sputtered Tb-Fe thin films prepared with a composition of 45∼50 at% Tb-Fe. Ar gas pressure of 4 mTorr, and rf power of 200 W. This material has astrong potential for use in magnetomechanical thin-film devices.

Structural origins of magnetic anisotropy in sputtered amorphous Tb-Fe films.

Using x-ray-absorption fine-structure measurements we have obtained clear evidence for structural anisotropy in amorphous sputter-deposited TbFe films exhibiting perpendicular magnetic anisotropy. Modeling of the data shows that perpendicular anisotropy in these films is associated with Fe-Fe and Tb-Tb pair correlations which are greater in plane and Tb-Fe correlations which are greater perpendicular to the film plane. Upon annealing at 300 \ifmmode^\circ\else\textdegree\fi{}C the measured structural anisotropy disappears and the magnetic anisotropy decreases to a level consistent with magnetoelastic interactions between the film and substrate.