TbFe Thin Films Research Articles

Understanding thickness dependent magnetic properties of Tb-Fe thin films

In this paper, we have attempted to understand the magnetic behaviour of Tb-Fe thin films grown with different thicknesses through detailed electron microscopy, magnetization measurements and magnetic domain imaging studies. Tb-Fe thin films over a range of thicknesses such as 50, 100, 200, 400, 600 and 800 nm were deposited on Si substrates using electron beam evaporation technique. Grazing incidence X-ray diffraction studies revealed that all the films were amorphous in nature. Microstructural studies using transmission electron microscopy showed columnar channel of voids extending from substrate to film surface. Magnetization measurements along the in-plane and out-of-plane direction indicated presence of out-of-plane magnetic anisotropy in all the films. Saturation magnetization and coercivity measured along the out-of-plane direction were found to vary with the thickness of the films. A very high coercivity of ~2000 mT was obtained for the film having thickness of 400 nm. Magnetic anisotropy calculations indicated a strong perpendicular magnetic anisotropy for the 400 nm thick film. The variation of magnetic anisotropy with film thickness was correlated with the magnetic domain patterns observed in the films using magnetic force microscopy.

Effect of Ti underlayer thickness on the magnetic anisotropy of TbFe thin films

In this study, we address the impact of Ti underlayer thickness (UL: 0-40 nm) on the structural, magnetic, and microscopic properties of TbFe thin films. The structural analysis confirmed the intermixing at interfaces of the Ti and TbFe layer with the increment of UL thicknesses. Out-of-plane (OOP) coercivity (\({H_{\rm{c}}}\)), and saturation field (\({H_{\rm{s}}}\)) gradually increased with an increase in UL thickness. For UL = 10 nm, the domain contrast and OOP stray field strength were enhanced, which may be due to the extent of d-d hybridization dominated over the influence of interfacial roughness. While for UL = 20, and 40 nm, the extent of interfacial roughness dominated the hybridization effects. In the case of UL: 20 nm, \({H_{\rm{c}}}\) increased by nearly 6 times more than the bare TbFe system. We observed a state with high OOP \({H_{\rm{c}}}\) combined with nearly zero OOP stray fields that are found to coexist in the sample. The magnetization reversal studies on a large area reveal domain nucleation followed by domain wall motion in all the films. The idea of tuning magnetic properties by varying thicknesses of Ti UL may be useful in spintronics applications.

Pervasive artifacts revealed from magnetometry measurements of rare earth-transition metal thin films

A class of artifacts manifesting as soft magnetic components are revealed from magnetometry measurements of rare earth-transition metal (TbFe) thin films prepared by magnetron sputtering. They are not inherent to TbFe, but are a direct result of the manner in which the substrates are mounted prior to sample fabrication, with a material deposited at the substrate sides giving rise to a significant magnetic moment. The authors find the same artifacts to also be present in rare earth-free [Co/Pt] multilayers. Trying to supress the appearance of this type of artifact has an influence on the coercivity and, in some cases, on the shape of the reversal curves. Care needs to be taken during fabrication to ensure reliable and reproducible samples so that sensitive magnetic parameters, such as coercivity and compensation points, can be extracted accurately and that data are not misinterpreted for even more complex systems. This type of artifact is not limited to samples prepared by sputtering but can extend to other conventional thin-film deposition methods.

Deviations from bulk behavior in TbFe(Co) thin films: Interfaces contribution in the biased composition

Ferrimagnetic TbFe or TbFeCo amorphous alloy thin films have been grown by co-evaporation in ultra-high vacuum. They exhibit an out-of-plane magnetic anisotropy up to their Curie temperature with a nucleation and propagation reversal mechanism suitable for current induced domain wall motion. Rutherford back scattering experiments confirmed a fine control of the Tb depth-integrated composition within the evaporation process. However, a large set of experimental techniques were used to evidence an interface related contribution in such thin films as compared to much thicker samples. In particular, scanning transmission electron microscopy experiments evidence a depth dependent composition and perturbed top and bottom interfaces with preferential oxidation and diffusion of terbium. Despite of that, amorphous and homogeneous alloy film remains in a bulk-like part. The composition of that bulk-like part of the magnetic layer, labeled as effective composition, is biased when compared with the depth-integrated composition. The magnetic properties of the film are mostly dictated by this effective composition, which we show changes with different top and bottom interfaces.

Strain-Modulated Exchange-Spring Magnetic Behavior in Amorphous Tb-Fe Thin Films

Using strain to manipulate magnetization at the nanoscale is attractive, due to its relatively high energy efficiency, but typically produces 90\ifmmode^\circ\else\textdegree\fi{} reorientation, rather than the 180\ifmmode^\circ\else\textdegree\fi{} flipping desired for spintronic applications. Using a compositionally graded film of the ferrimagnetic alloy Tb-Fe, the authors achieve strain-induced 180\ifmmode^\circ\else\textdegree\fi{} magnetization rotation. The applied strain induces magnetic anisotropy in the Tb-dominant region, reversing the magnetic moment of the exchange-coupled Fe-dominant region. This is a promising development for spintronics based on voltage-controlled ``exchange springs''.

Anomalous Hall effect studies on Tb–Fe thin films

TbxFe100−x (with x=11, 25, 31 and 44) thin films were prepared with the substrates kept at a temperature of 300°C and the Hall resistivities and electrical resistivities were investigated in the temperature range 25–300K. The sign of Hall resistivity is found to change from positive for x=31 to negative for x=44 film at temperatures 25K and 300K, reflecting the compensation of Tb and Fe magnetic moments between these two compositions. Perpendicular magnetic anisotropy was observed in the films of x=25 and 31 at 25K as well as at 300K. The Hall resistivity is seen to increase for the films of x=11 and 31 with increasing temperature, while it decreases for the films of x=25 and 44 with increasing temperature. The temperature coefficients of electrical resistivities of these films are seen to be positive. The presence of perpendicular magnetic anisotropy (refers to magnetic anisotropy, in this paper) in the temperature range 25–300K in Tb25Fe75 and Tb31Fe69 and their metallic nature are indicators that the Tb–Fe films deposited at higher temperatures are more suitable for magneto optic data storage applications than their amorphous counterparts, due to the stability of the former.

Modeling of Temperature Dependence of Magnetization in TbFe Films — An Atomistic Spin Simulation Study

In this paper, we performed spin simulations at atomistic level to study the temperature dependent properties of perpendicularly magnetized TbFe thin films. The crystallographically amorphous feature of TbFe ferrimagnetic alloys is modeled by using a lattice system with disordered site occupation of rare earth (RE) and transition metal (TM) spins. The simulated Curie temperature ([Formula: see text]) is consistent well with the mean-field approximation theory. With the increase of Tb concentration, the [Formula: see text] decreases almost linearly, whereas the magnetization compensation temperature ([Formula: see text]) increases gradually until the [Formula: see text] value is reached. The inter-sublattice exchange coupling strength [Formula: see text] between the RE and TM atoms can significantly affect [Formula: see text], but has less impact on [Formula: see text]. With the increase of Tb concentration, the TbFe sample of high [Formula: see text] exhibits a much faster increase in [Formula: see text] than the sample with low [Formula: see text]. Moreover, we have tested the simulation code to model the laser pulse induced ultrafast nonequilibrium spin dynamics. As an example, the femto-second pulse laser induced demagnetization and recovery process is clearly reproduced. These features are in a good agreement with the experiments, indicating that the simulation model can capture the basic physics in describing the high temperature dependent magnetic property as well as the ultrafast spin dynamics.

Magneto-optical response of ferrimagnetic Tb-Fe thin films in the visible and ultraviolet range

We present wavelength-dependent measurements of Kerr rotation and ellipticity for ferrimagnetic Tb30Fe70 thin films in the optical range of 225 nm–726 nm (1.7 eV to 5.5 eV). The thicknesses of the magnetic layers vary from 19 nm to 83 nm. Strong optical interference effects in the magneto-optical spectra are observed for films grown on commonly used SiO2/Si substrates, which may easily be misinterpreted as spectral signatures of Tb. This strong optical interference feature can be fully suppressed by depositing magnetic Tb-Fe films on glass substrates.

Effect of sputtering parameters on the structure, microstructure and magnetic properties of Tb-Fe films

The effect of sputtering parameters such as gas pressure and power on the structure, microstructure and magnetic properties of sputtered Tb-Fe thin films was investigated. X-ray diffraction and transmission electron microscopy studies showed that all the films were amorphous in nature irrespective of the sputtering parameters. A fine island kind of morphology was observed at low sputtering power whereas large clusters were seen at higher sputtering power. While the composition of Tb-Fe films remained constant with increasing sputtering power, the magnetic behaviour was found to change from superparamagnetic to ferromagnetic. On the other hand, the increase in argon gas pressure was found to deplete the iron concentration in Tb-Fe thin films, which in turn reduced the anisotropy and Curie temperature. Annealing of the films at 773 K did not result in any crystallization and the magnetic properties were also found to remain unchanged. (C) 2015 Elsevier B.V. All rights reserved.

Dependence of all-optical magnetic switching on the sublattice magnetization orientation in Tb-Fe thin films

We demonstrate that the direction of all-optical switching (AOS) in rare-earth transition-metal (RE-TM) alloy Tb-Fe thin films depends on the orientation of the sublattice magnetization and not on the direction of the resulting net magnetization. For this purpose, we investigated the AOS ability for a sample dominated by the Fe sublattice magnetization (Tb24Fe76) and another dominated by the Tb sublattice (Tb30Fe70). This finding of the sublattice dependence of AOS contributes to the understanding of switching in RE-TM multilayered thin films and heterostructures.

All-optical helicity dependent magnetic switching in Tb-Fe thin films with a MHz laser oscillator.

We demonstrate all-optical magnetic switching (AOS) in an amorphous Tb30Fe70 thin film, triggered by a 5.1 MHz laser oscillator. The magnetic layer is grown on SiO2/Si substrate. An identical magnetic film deposited on a microscope glass slide reveals no AOS but solely thermally induced demagnetization. This effect is due to heat accumulation by multiple laser pulses because of the low thermal conductivity of the glass substrate. In contrast, the use of a proper heat sink (e.g. SiO2/Si) avoids the need for low repetitive laser amplifier systems to induce AOS and paves the way for a cheap and simple technical implementation using conventional laser oscillators.

Microscopic magnetic properties of an oxygen-doped Tb-Fe thin film by magnetic Compton scattering

The magnetic Compton scattering of a Tb32Fe55O13 film was measured in order to investigate the microscopic magnetization processes (i.e., the spin moment, orbital moment, and element specific moments). The trend of the spin magnetic moment was the same as that of the total magnetic moment but opposite to the orbital magnetic moment. In the low magnetic field region, the magnetic moments were not perfectly aligned perpendicular to the film surface, and the perpendicular components were found to mainly arise from the magnetic moment of Tb. Oxygen atoms hinder long range magnetic interaction and hence also affect the magnetization process of the magnetic moments of Tb and Fe.

ChemInform Abstract: Corrosion Mechanism of Sputter-Deposited TbFe Thin Films in Aqueous Environment.

This paper reports on the corrosion mechanism of sputter-deposited TbFe thin films for magneto-optical recording material that was investigated using electrochemical methods in aqueous environment with and without Cl{sup {minus}} ions. TbFe thin films with varying composition prepared by an ion beam sputtering method were used as specimens. TbFe tape alloys made by the rapid quench method of melting alloys were also used for comparison. In an acid buffer solution without Cl{sup {minus}} ions, the corrosion rate of the TbFe thin films and tape alloys decreased with increasing Tb content. In this solution, passive films composed of Tb oxide or hydroxide were formed on both the TbFe thin films and tapes and the selective dissolution of Fe through the passive films occurred. In neutral solutions with Cl{sup {minus}} ions, pitting corrosion occurred on both the TbFe thin films and tapes. The stoichiometric dissolution of the substrate at pitted sites and the selective dissolution through the passive films at nonpitted sites take place in these solutions.

Effect of anisotropy on anomalous Hall effect in Tb–Fe thin films

The electrical and Hall resistivities of TbxFe100−x thin films in the temperature range 13–300 K were investigated. The sign of Hall resistivity at 300 K is found to change from positive for x=28 film to negative for x=30 film, in accordance with the compensation of Tb and Fe moments. All the films are seen to have planar magnetic anisotropy at 13 K. The temperature coefficients of electrical resistivities of the amorphous films with 19≤x≤51 are seen to be negative. The temperature dependence of Hall resistivity of these films is explained on the basis of random magnetic anisotropy model. The temperature dependences of Hall resistivities of the x=22 and 41 films are seen to exhibit a nonmonotonous behavior due to change in anisotropy from perpendicular to planar. The same behavior is considered for the explanation regarding the probable formation of Berry phase curvature in these films.

A nonlinear magnetomechanical coupling model of giant magnetostrictive thin films at low magnetic fields

As magnetomechanical coupling model plays an important role in the application of giant magnetostrictive thin films (GMFs) to the microactuators and the microsensors, in this paper, the properties of GMFs at low magnetic fields, including the large magnetostriction, the soft magnetization and the hysteresis under internal stress (prestress), are analyzed firstly. Thereafter, with neglecting the change of internal stress during magnetic polarization and magnetostriction, a nonlinear magnetomechanical coupling model of GMFs at low magnetic fields is established, which is composed of the modified Rayleigh model for the magnetic polarization and the “butterfly curve” model for the strain. Experiments on TbDyFe-polyimide (PI)-SmFe and TbDyFe-Cu-SmFe are conducted, respectively, to verify the proposed model. Results indicate that the model curve coincides well with the experimental results of the magnetic polarization and the magnetostriction for TbDyFe-PI-SmFe and TbDyFe-Cu-SmFe under a given prestress at a low magnetic field. Besides, the proposed model is also in good conformity with the published experimental data of TbFe, SmFe and TbDyFe thin films.

正・負超磁歪薄膜で構成される高感度複合運動機能素子

Composite mover device constructed with both negative and positive magnetostrictive thin films on each side surface of silicon substrate were prepared by DC magnetron sputtering process. The magnetic field induced mover strain (an apparent magnetostriction) of composite mover device at 150 kA/m of magnetic field was as same as the sum of magnetostriction values of Sm-Fe negative and Tb-Fe positive magnetostrictive thin films. Although the magnetostrictive susceptibility of Sm-Fe negative and Tb-Fe positive magnetostrictive thin films were over 8.6 and 5.42 ppm/kA•m-1, respectively, an apparent magnetostrictive susceptibility of the composite mover device was 36.4 ppm/kA•m-1. We concluded that composite process tremendously enhanced the apparent magnetostrictive susceptibility. Composite mover device with high responsiveness was developed.

Influence of rapid cycle annealing temperature on the properties of Tb-Fe magnetostrictive films

In this paper, magnetostrictive Tb-Fe thin films were prepared by DC magnetron sputtering and then heat treated using rapid cycle annealing. The influences of annealing temperature on the phases and magnetic properties are discussed. Results show that increasing annealing temperature can promote the formation of BCC-Fe nanocrystals and cause oxidation of the rare earth element. Annealing does increase the domain size and result in domain boundary irregularities relative to the as-deposited film. Higher temperature has little effect on the domain structure. Magnetization at filed of 1600kA/m is first increased with annealing temperature because of the precipitation of Fe and then decreased because of the oxidation. The latter also caused the coercivity increase when the annealing temperature is above 500°C. Maximum magnetostriction coefficient of ∼145ppm at 40kA/m was obtained for 300°C and 500°C annealed samples.

Fabrication condition effects on the magnetic and magnetostrictive properties of sputtered Tb-Fe thin films

Magnetic and magnetostrictive properties of amorphous Tb-Fe thin films are investigated as functions of sputtering conditions such as the substrate thickness, input power, sputtering time, and coverage area ratio of coated thin film to substrate. The observed magnetic and magnetostrictive properties are well explained in terms of the macroscopic tensile stress, which is formed due to the difference of the thermal expansion coefficients between the thin film and substrate, and an annealing effect. The macroscopic tensile stress enhances in-plane anisotropy, and the annealing effect mainly reduces local residual stress introduced during sputtering. At sputtering conditions corresponding to a high thin-film/substrate temperature, the macroscopic tensile and an annealing effect are high, causing the magnetostriction sensitivity to increase at low magnetic fields, coercivity, and remanence ratio.

Magnetic force microscopy study on amorphous TbFe thin films

By using magnetic force microscope (MFM), honeycomb domain structures were found in the as-deposited amorphous TbFe thin films with perpendicular magnetic anisotropy. The domain structures were composed of many small white round dots embedded in the black matrix, which formed an irregular hexagonal pattern with some deformation. MFM measurements were performed with various scanning heights and opposite tip magnetization directions. The z component of both the magnetization and the stray field of the dots were determined quantitatively within the point probe approximation. Charge contrast and susceptibility contrast were separated by forming the difference and sum of two images with opposite tip magnetization.

Ion irradiation effects on magnetostriction of Tb–Fe thin film

Giant magnetostrictive TbFe 2 thin films were prepared by the ion plating process. The films were treated by Ar plasma irradiation and heat-treatment. The plasma irradiation was carried out at low plasma energy by a high heat flux sheet plasma system. Both treatments lead to the increase in the maximum magnetostriction and the magnetostrictive susceptibility at low magnetic field. The plasma irradiation effects seem to be due to the heat generation during irradiation. The magnetostrictive characteristics are affected by the increase in in-plane anisotropy magnetization by treatments.