TbFe Films Research Articles

High Remanence in Laminated TbFe Films

Single- and multi-layer high saturation magnetization TbFe films with high rectangularity were studied to obtain a film with high remanence. Lamination resulted in greatly improved remanence. No significant variation in M <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">r</sub> and H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> is observed in single-layer and double-layer films, but the remanence ratio for films of three layers or more is almost one and the H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> increases significantly. At three layers M <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">r</sub> becomes 300 G, a very high value compared with single-layer films. Though K <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">u</sub> decreases monotonically with increase in lamination and H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">k</sub> = 2K <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">⊥</sub> /M <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">s</sub> decreases too, H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">C</sub> increases resulting in high remanence.

Preparation of High Remanence TbFe Films

The remanence of amorphous TbFe films with perpendicular anisotropy deposited by several deposition methods was investigated. The uniaxial anisotropy was enhanced in films deposited onto rotating substrates. The coercivity increased with dual gun sputtering compared to single gun sputtering. The remanence did not depend on the anisotropy directly but was mainly related to the wall coercivity. In dual gun rf magnetron sputter-deposited films onto rotating substrates, the wall coercivity was so large that magnetization rotation dominated the magnetization reversal, resulting in high remanence. The wall coercivity also increased in laminated films. A high remanence of 300 Gs with a residual ratio of 1 has been obtained in Tb31Fe69 films produced with a repetition of the deposition of a 0.5 µm thick lamina and the time intervals between the sputtering of each lamina.

Amorphous Tb¿Fe Magnetic Thin Films Prepared by Flash Evaporation

Variation in the magnetization curve of amorphous Tb-Fe films prepared by the flash evaporation method while the substrate temperature is varied was studied to clarify the mechanism responsible for perpendicular anisotropy and high coercivity. It was found that a film prepared at a 473 K substrate temperature was a typical perpendicular magnetization film, but in a film prepared at a 77 K substrate temperature, the coercivity and remanence of the hysteresis loop measured in the in-plane direction were both high, suggesting that anisotropy occurs in the in-plane direction.

Highly stable indium alloyed TbFe amorphous films for magneto-optic memory

Indium alloyed TbFe amorphous films for use as a magneto-optic memory are proposed and studied. These TbFeIn films show strong resistance to corrosion and oxidation. Indium is effective in suppressing oxygen diffusion into the films. An oxygen diffusion coefficient of 5×10−25 m2/s is calculated for TbFeIn films incubated at room temperature. Activation energy is 1.3 eV. This value is over 1.5 times larger than that of TbFe films, where the value is obtained with ellipsometry measurements by R. Allen and G. A. N. Connell [J. Appl. Phys. 53, 2353 (1982)].

High-corrosion-resistant magneto-optical recording media using TbFeCoTi films

The effects of adding Ti to TbFe and TbFeCo films with and without protective layers were studied. The addition of Ti improved the corrosion resistance of the films. The transmittance of TbFeCo films was reduced by a factor of 10 by the substitution of 5% Ti for Fe, and by a factor of 100 by the substitution of 10% Ti for Fe. Pit formations in TbFeCo during aging in a corrosive condition and immersion in a NaCl solution were almost completely eliminated by the substitution of 5% Ti for Fe. The Kerr rotation angle (θk) decreased slightly in TbFeCo by the substitution of 10% Ti for Fe, while improving the corrosion resistance.

Corrosion Resistance of Magneto¿Optical Recording Media

The effects of adding Ti to TbFe and TbCoFe films with and without protective layers were studied. The addition of Ti improved the corrosion resistance of the films more effectively than an SiO2 protective layer. 10 percent Ti tripled the corrosion resistance of TbFe films and doubled that of TbCoFe films. Pit formation during aging and immersion in brine was eliminated almost completely by the addition of 5 percent Ti, which also increased the Kerr rotation angle (θK) slightly in TbFe and TbCoFe films. 10 percent Ti lowered θK somewhat while improving the corrosion resistance.

Improvement of Lifetimes of Magneto¿Optical Disks by Alloying Various Elements

Various elements were added to TbFe and TbFeCo films and their effects were studied. The addition of Al, Ti, Cr, or Pt was found to inhibit both pinhole growth and corrosion. The addition of Pt not only increased the Kerr rotation angle (θ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">K</sub> ), but also completely halted the deterioration of θ <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">K</sub> .

Aging Changes of Some Properties of Amorphous TbFeAl Thin Films as a Magneto-Optical Recording Medium

The effect of Al addition on the deterioration of TbFeAl films is discussed. Oxidation of films with no protective layer was observed at temperatures between 100° and 200° C. Variation in the transmittance was attributed to the varying thickness of the oxidation layer. No pinholes were observed. The addition of Al to TbFe film reduces room temperature oxidation by a factor of 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">7</sup> .

Dependence of microstructure and magneto-optical properties on deposition angle in evaporated TbFe and TbFeCo films

We have investigated the effects of deposition angle on growth morphology and magneto-optical properties in TbFe and TbFeCo films, which were prepared by coevaporation of Tb and Fe (or FeCo) on tilted substrates. Cross-sectional scanning electron microscopy revealed that the films had columnar structure and the growth orientations of columns generally followed the ‘‘tangent rule’’ [Dirks and Leamy, Thin Solid Films 47, 219 (1977)]. Measurements of the polar Kerr hysteresis loops revealed that with increasing the angle of incidence of the vapor beam from the substrate normal, the squareness of the hysteresis loop deteriorated, and also the Kerr rotation angle and the coercivity decreased. The results of the present study clearly demonstrate the importance of normal growth of columns with respect to a film plane to achieve perpendicular magnetic anisotropy in evaporated rare-earth transition-metal alloy films.

Observation of laser-written magnetic domains in amorphous TbFe films by Lorentz microscopy (invited)

A review is given of Lorentz microscopy and its application to the study of laser-written domains in amorphous rare-earth/transition-metal–type materials. Domains, or regions of reverse magnetization, were written under various conditions of laser power and applied magnetic field in TbxFe1−x films where x varies in the range 0.14–0.32. Upon examination by Lorentz microscopy, and under certain conditions, these written regions show highly detailed magnetic structures. One condition for obtaining good images is the avoidance of oxidized surface layers showing in-plane magnetization. Another condition is tilting of the film plane in the transmission electron microscope to enhance image contrast. A variety of domain structures have been observed ranging from fully saturated regions with both highly regular and irregular boundaries, to fully demagnetized regions. An example of correlation between the field dependence of the microstructure and measurements of magneto-optical signal is given for the x=0.32 composition. Results are presented of carrier signal and noise measurements made on a film on a rotating disk.

Thickness Dependence of Effective Composition for Amorphous TbFe Films

An attempt is made to explain the deviation to the Fe-rich side of the ``effective'' composition of RF sputtered, amorphous TbFe films. The results indicate that the effective composition apparently varies as a function of film thickness, and this cannot be explained using the present model. A thin boundary-layer model is proposed which assumes: 1) these layers are formed at both the film-substrate and film-air boundaries; 2) this layer thickness is independent of the total film thickness; and 3) there are exchange couplings between the boundary layer and the middle layer.

The Effects of Sm on Amorphous Gd-Fe Thin Films

Sm was added to GdFe films to make GdSmFe amorphous films and their magnetic characteristics were studied. It was found that GdSmFe films with quality equal to TbFe films could be produced. This indicates that GdSmFe could be viable as a magneto-optical medium.

Magnetic Properties of Composition Modulated Amorphous Zr¿Fe/Tb¿Fe Multilayered Films Prepared by RF Sputtering Method

The changes in structure and saturation magnetization (4πM <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">s</sub> ) due to composition modulation period (D), Curie temperature (T <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</sub> ), perpendicular magnetic anisotropy (K <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">u</sub> ), and polar Kerr rotation in composition modulated multilayered films with amorphous Zr-Fe films and amorphous Tb-Fe films superimposed were studied. It was found that as D <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sub> , the composition modulation period calculated from the first X-ray diffraction peak, gets thinner, 4πM <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">s</sub> increases. This can be explained by the fact that magnetization of Fe within the Zr-Fe film is induced by the Tb-Fe film.

Ar pressure dependence of saturation magnetization and film composition in TbCo and tbfe sputtered films

AbstractThe argon pressure dependence of saturation magnetization MS and film composition in TbCo and TbFe sputtered films under the substrate bias VB × 0 was investigated. It was found that the change in the shape of multitarget surfaces influences MS strongly. When the sputtering period was 60 min, the Ar pressure dependence of MS and the film composition were different in TbCo and TbFe films. This was found to be due to the existence of the composition gradient in the direction of the film thickness in the TbFe film deposited under high Ar pressure. As a result of investigating the multitarget surfaces, the Tb chip surface was found to be contaminated by TM atoms (Co, Fe) and the intermetallic compound was formed. On the other hand, the TM target surface was clean. The surface condition of the Tb chip was different in the Tb ‐ Co and Tb ‐ Fe multitargets. The Tb surface of the Tb ‐ Fe target was covered with cone‐shaped projections, causing the composition gradient in the film thickness direction when the Ar pressure was high. When the sputtering period was short (shorter than 12 min), the composition ratio against NTM/NTb) against MS and Tb decreases with the increase of Ar pressure in both depositions of TbCo and TbFe films.

MAGNETO-OPTICAL KEEP EFFECT OF PtMnSb/TbFe MULTILAYERED FILMS

Coupling effects between PtMnSb and TbFe films with a double-layered structure have been investigated to improve the magnetic and magneto-optical properties of PtMnSb film with in-plane magnetization. A weak exchange-coupling was recognized for a PtMnSb/TbFe double-layered film in which a very thin PtMnSb layer (∼200Å thick) was combined with thick amorphous TbFe layer (∼6000Å thick). The coercive force Hc of the structure increased up to 6300e, which was five times as large as a PtMnSb film. The polar Kerr rotation loop of double-layered structure could be explained in terms of an exchange coupling model.

FINITE ELEMENT ANALYSIS OF PULSED LASER BEAM INDUCED TEMPERATURE PROFILES IN MAGNETO-OPTIC RECORDING THIN FILMS

Variation of temperature profiles during the magneto-optic recording process in monolayered TbFe and GdCo thin film was analyzed by the two-dimensional finite element method. The effects of laser power and film thickness on the heating behavior of the film were mainly examined as the major parameters to determine the recorded bit size. It has been shown that maximum local temperature rise on the surface of film at the beam center can be estimated by a simple relation to the film thickness.

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.

Stability phenomena in amorphous rare earth-transition metal films

TbFe films have been prepared with a range of compositions near to the room temperature compensation point and subjected to annealing at 100°C for up to 800 hours. Measurements of magnetic properties as a function of anneal time revealed a decrease in coercivity coupled with an increase in saturation magnetisation for all compositions. Changes in M s appeared to conform to a Johnson-Mehl-Avrami. exponent of approximately 0.5. Rutherford back-scattering spectrometry and electron microscopy revealed that the most likely cause of the observed changes in magnetic properties was oxygen diffusion resulting in the formation of TbO n oxides in turn leading to local diffusion, segregation and crystallisation of b.c.c, α-iron. The addition of an aluminium protective overlayer stablised the films against these changes, at least for the time and temperature ranges studied.

Amorphous RE-TR magnetic alloys formed by ion mixing

Rare earth-transition metal (RE-TR) alloys are well known for their excellent magnetic properties, especially in the amorphous state. In recent years, some RE-TR alloys have been used as the recording matrix of the magneto-optical disk, in which only very thin film is required. Ion mixing is a suitable method for producing amorphous alloy films and this study was undertaken to investigate the possibility of ion mixing as an alternative way to produce such kind of magnetic alloy films. Various binary, ternary and even quadrunary combinations among RE (Gd, Tb, Nd) and TR (Fe, Cc) metals were studied by 300 keV Xe ion mixing of multilayered samples at LN 2 or room temperature. Generally speaking, amorphous alloys were formed after adequate dose irradiation, while metastable crystalline phases were observed at relatively low dose mixing stages. Ten amorphous RE-TR alloys were obtained and their Kerr rotating angles, i.e. the changing of the polarized angle between the incident and reflected laser beams interacting with the alloy surface, were measured by a He-Ne laser with a wavelength of 632.8 nm. It was found that the Kerr rotating angles of the ion mixed films were comparable or even superior to those of the alloys manufactured by sputtering technique, e.g. a Kerr angle of 48′35″ was observed for a Tb-Fe film so obtained. Experimental results of ion induced amorphous phase formation as well as the magnetic properties of the ion mixed films are reported and discussed.

Anisotropy dispersion and its influence on magneto-optical effect in rare-earth transition-metal amorphous films

Magnetic anisotropy dispersion in sputter-deposited rare-earth transition-metal amorphous films is measured by the methods of Hall hysteresis loops and torque magnetometry. The inhomogeneity in the orientation of the easy axes of magnetization is found to be rather large; the mean inclination angle of the axes from film normal is 16.5° in a Gd–Tb–Fe film. Results show a clear correspondence between the anisotropy dispersion and Kerr rotation angle, and both depend on the bias voltage applied to the substrates during sputtering. Anisotropy dispersion is an important property for evaluating the amorphous magnetic films for magneto-optical storage application.