Amorphous TbFe Thin Films Research Articles

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''.

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.

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.

Structural and magnetic length scales in amorphous TbFe 2

Magnetic phenomena in amorphous Tb–Fe thin films are related to structure on a variety of length scales. For instance, perpendicular magnetic anisotropy appears to be related primarily to short-range compositional and/or topological ordering. In this paper, we demonstrate that structure on longer length scales influences domain wall pinning and the morphology of the magnetic domains. Amorphous TbFe 2 films thicker than approximately 1 μ m that possess large perpendicular magnetic anisotropy have very long magnetic correlation lengths (50–70 nm, as determined previously by small-angle neutron scattering) and strongly asymmetric magnetic domains. Using small-angle X-ray scattering (SAXS), we show that such films show a well-defined structure with a characteristic length scale of approximately 57 nm. The structure of films grown at lower temperatures (with lower magnetic anisotropy K u but higher coercivity), shows a much broader distribution of length scales. We propose that the characteristic structure seen in SAXS is the source of domain wall pinning, which in turn determines the length scale of the magnetic domains, as well as the magnetic correlation length and coercivity. We also observe an in-plane anisotropy of the structure, which is likely related to the asymmetry of the magnetic domains and the anisotropy of the magnetic correlation length.

Honeycomb domain structures in amorphous TbFe thin films

The magnetic properties and domain structure of amorphous TbFe thin films were studied by magnetic measurement and magnetic force microscope. Honeycomb domain structures were found in the as-deposited amorphous film. 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. The average dot size was about 450 nm, with an average separation of 610 nm. The derived domain wall energy density γ and the exchange constant A were 0.95×10−2 and 1.79×10−11 J/m, respectively.

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.

Anisotropy, magnetostriction and local chemical order in amorphous TbxFe1-x (0.1

Local chemical order in amorphous TbFe thin films has been investigated in a variety of compositions, using EXAFS, magnetostriction and anisotropy measurements. Data reported here are consistent with a density of FeTb pairs in the film plane larger than in the perpendicular direction.

Pair Ordering Anisotropy In Amorphous Tb-Fe Thin Films

ABSTRACTWe have studied the structural origins of perpendicular magnetic anisotropy in amorphous Tb-Fe thin films by employing high energy x-ray scattering. The as-deposited films show a clear structural anisotropy, with a preference for Fe-Tb near-neighbors to align in the out-of-plane direction. Upon annealing, the magnetic anisotropy energy drops significantly, and we see a corresponding reduction in the structural anisotropy. The radial distribution functions indicate that the number of Fe-Tb near-neighbors increases in the in-plane direction, but does not change in the out-of-plane direction. Therefore, the distribution of Fe-Tb near-neighbors becomes more uniform upon annealing. We conclude that the observed reduction in perpendicular magnetic anisotropy energy is a result of this change in structure.

磁性薄膜を用いたマイクロアクチュエータの試作

We made magnetostrietive actuators and electromagnetic actuators by using various kinds of magnetic thin film. The magnetostrictive actuators were bimorph cantilever actuators and a traveling machine, composed of magnetostrictive amorphous Tb-Fe and Sm-Fe thin films on a polyirmide substrate. The 3-mm-long cantilever actuator using a 3-μm-thick substrate exhibited large deflection above 100μm in magnetic fields as low as 24 kA/m, and above 500 μm at a resonant frequency of 29 Hz in an alternating magnetic field of 24 kA/m. The electromagnetic actuators are driven by magnetic torque, which made “flying” actuation possible. These magnetic actuators need no power supply cables, because they are driven by an external magnetic field.

Surface and bulk magnetic anisotropy in amorphous TbFe/SiN trilayered films

Magnetic perpendicular anisotropy constants of RF-sputtered amorphous TbFe thin films are measured by VSM and magnetooptic techniques. Anisotropy depends heavily on film thickness. It is found that the spontaneous magnetization changes with thickness in the same fashion as in the presence of a very thin (1 nm) highly magnetized interface layer. Anisotropy measured from the top and bottom film surfaces reveals a very different dependence on the deposition parameters. Because the magnetization reversal is incoherent due to the different anisotropy fields in the surface layers and in the bulk, it is necessary to account for the reveal mechanism to evaluate the true value of intrinsic anisotropy of the amorphous alloy.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Dependence of magnetostriction of sputtered Tb-Fe films on preparation conditions

Amorphous Tb-Fe thin films prepared by the sputtering method in the compositional range Tb/sub x/Fe/sub 1-x/ (x=0-0.5) are investigated in view of their potential for use in electromagnetic thin film actuators. The magnetostriction and the coercive force for the Tb-Fe films are examined for different sputtering conditions to obtain both soft magnetic properties and large magnetostriction in this system. As a result, Tb-Fe thin films having large magnetostrictions (180*10/sup -6/ at 1 kOe) and low coercive force (60-70 Oe) are obtained. These films are prepared under the conditions of the composition of 45-50 at.% Tb, Ar gas pressure of 4 mTorr, RF input power of 200 W and using water cooled substrates. A trial actuator using magnetostrictive thin films is also reported. >

Magnetic properties of ferrimagnetic rare-earth—transition-metal films and multilayers

In this paper we present a brief report on magnetization studies of three different types of rare-earth—transition-metal ferrimagnetic thin films. The first consists of compositionally modulated Gd 0.15Fe 0.85/Gd 0.40Fe 0.60 where the two compositions are on different sides of the magnetic compensation point (Gd 0.26Fe 0.74) at room temperature. The compositionally modulated layers therefore form an artificial (macroscopic) superlattice antiferromagnet which exhibits both spin-flop transitions and enhanced in-plane anisotropy owing to classical dipolar effects. We also report magnetization measurements on a homogeneous film of Tb 0.23Fe 0.77, which exhibits large perpendicular anisotropy typical of amorphous TbFe thin films as well as a spin-flop transition near 60 kOe. Finally, we present data on a film of Gd 0.40Fe 0.60(300 Å)/Fe(10 Å)/Pd(100 Å)/Fe(30 Å) which demonstrates a practical method of determining the strength of ferromagnetic coupling between two magnetic layers from simple magnetization measurements.

Studies of the structure and magnetic properties of amorphous Tb-Fe thin films

Amorphous Tb-Fe films with various thicknesses were prepared at substrate temperatures T sub = 300 and 473 K by flash evaporation, and their structures and magnetic properties have been investigated. The films prepared by the present method are considerably uniform in composition and structure. The magnetic uniaxial anisotropy of films prepared at T sub = 473 K is larger than that of films prepared at T sub = 300 K. It is found that the large angular dispersion of the local anisotropy takes place near the top surface in common when the film thickness is large irrespectively of T sub. The reason will be attributable to the random close packing of Tb atoms, originated from the amorphous nature.

Magnetic properties and structure of rare-earth-transition-metal thin films implanted with Ar + ions

Changes in the local magnetic properties and structure of amorphous TbFe thin films, induced by ion implantation, have been investigated in comparison with amorphous GdCo thin films. The samples were obtained by rf co-sputtering on glass substrates. X-ray diffraction and Rutherford backscattering spectrometry (RBS) have been used for structural and compositional analysis. Local hysteresis loops and coercive forces were studied by magneto-optic polar Kerr effect. Structural investigations showed the films to be completely amorphous, before as well as after implantation. Magneto-optical measurements pointed to a progressive diminution of local hysteresis loop area and to a specific behaviour of the relative coercive force for TbFe and GdCo samples, with increasing dose. Both effects were explained by the alteration of magnetic properties in the implanted layer.

Domain formation characteristics during thermomagnetic recording for amorphous TbFe and TbFeCo alloy thin films

The configurational characteristics of thermomagnetically written domains under a static laser irradiation condition were observed by using a polarizing microscope. The shapes of the domains were categorized into three distinctly different types: (1) circular domains with size almost independent of the applied field, (2) domains growing in size and assuming smoother boundaries with increasing applied field, and (3) domains unrecordable at any condition. It was confirmed that the domain configurations were determined mainly by which one was the dominant controlling factor between demagnetizing and domain wall energy at elevated temperatures in the thermomagnetic recording process. The bit shape irregularity found in some alloys of TbFe was attributed to nonuniformity in magnetic properties inherent in the amorphous structure. >

Exafs Study of the Stability of Amorphous TbFe Thin Films

ABSTRACTEXAFS is used to measure the local atomic structure of Fe in Au doped Tb-Fe thin film alloys. The as deposited sample shows structural fcatures which are essentially identical to those of the undoped films. Au additions stabilizes the amorphous structure against recrystallization, however, the loss of magnetic anisotropy under thermal annealing is not reduced. This demonstrates that magnetic relaxation in these alloys does not involve crystallization of the amorphous structure.

Studies of Long Term Aging Effects on the Magneto-Optic Properties of Amorphous Tb-Fe Films

The real long term aging phenomena at ambient temperatures, over 8 years, of amorphous TbFe thin films protected with a SiO x layer has been investigated, using Kerr magneto-optic effect. Our data indicate significant changes in the coercivity values for films with less than 500A thickness. In thicker films structure/stress relaxation effects appear to be significant. Studies of the stability of these films under accelerated aging are also presented.

High-density Information Storage by Means of Magnetic Holography on Amorphous TbFe Thin Films (II)

The recording characteristics and hologram patterns of data storage by magnetic holography are described in detail. When the reconstruction was like a spatially filtered image of the original pattern, it was observed that the middle part of the contour of each character of the original pattern was saturated by the excess intensity of the object beam. It was found that the recording margin in magnetic holography is very small, and is strongly affected by the original data pattern. Adjustment of intensity of the object and reference beams at the recording stage is thus very important.

High-Density Information Storage by Means of Magnetic Holography of Amorphous TbFe Thin Films (II)

Previously we reported the possibility of recording information by means of magnetic holography (using amorphous TbFe thin films as a hologram medium) onto a spot of diameter less than 1 mm, reconstructing data using the Faraday effect. However, we had not studied the basic characteristics of information storage in detail, and therefore were not able to make good-quality holograms with good reproducibility. Because reproducibility is the characteristic of greatest importance for recording, we studied the recording margin for information storage by magnetic holography. In addition, we considered the relationship between the power density of the two beams (object beam and reference beam) and the domain pattern (hologram). It was confirmed that the domain pattern is closely related to the beam density, and the recording margin depends on the information pattern. From these results, we were able to create good-quality holograms with satisfactory reproducibility.

Properties of amorphous TbFe and GdFe thin films for perpendicular recording

The recording properties of magnetic media are closely related to their magnetization process but this process can seldom be directly observed. In this paper the relation which can be found between the perpendicular recording properties of amorphous TbFe and GdFe alloys and their magnetization processes as observed by magnetooptics is reported. In the Case of TbFe the Mr/Ms ratio is a function of the coercivity and the maximum recording density D <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">L</inf> is a growing function of Mr/Ms. On the other hand D <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">L</inf> depends on the rotating speed of the disc when writing. It is shown that this property can be related to the magnetization process of TbFe which is time dependent. GdFe media present a square hysteresis loop even if the coercivity H <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</inf> is low. D <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">L</inf> is a decreasing function of H <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</inf> . The domains nucleation process and the domains wall motion were observed by Kerr effect. The behaviour of the D <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">L</inf> (H <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</inf> ) function is derived from these measurements.