Amorphous TbFe Thin Films Research Articles

Effect of the oxidation on the magnetic properties of vacuum evaporated Tb-Fe thin films

An experimental device has been developed in order to study the magnetic properties of evaporated thin films inside the vacuum system. Amorphous Tb-Fe thin films were obtained and their in-plane magnetization curves measured by the magneto-optical transversal Kerr effect in vacuum and in the atmosphere. Remarkable changes have been observed in their saturation magnetization, initial permeability and coercivity immediately after the samples were exposed to the air. These changes seem to be due to the preferential oxidation of the rare earth.

Magnetic properties of amorphous Tb-Fe thin films with an artificially layered structure

An alternating terbium-iron (Tb-Fe) multilayer structure artificially made in amorphous Tb-Fe thin films gives rise to excellent magnetic properties of large perpendicular uniaxial anisotropy, large saturation magnetization, and large coercivity over a wide range of Tb composition in the films. The films are superior to amorphous Tb-Fe alloy thin films, especially when they are piled up with a monatomic layer of Tb and several atomic layers of Fe in an alternating fashion. Small-angle x-ray diffraction analysis confirmed the layering of monatomic layers of Tb and Fe, where the periodicity of the layers was found to be about 5.9 Å. Direct evidence for an artificially layered structure was obtained by transmission electron microscopic and Auger electron spectroscopic observations. Together with magnetic measurements of hysteresis loops and torque curves, it has been concluded that the most important origin of the large magnetic uniaxial anisotropy can be attributed to the Tb-Fe pairs aligned perpendicular to the films.

Effect of oxidation on the magnetic properties of unprotected TbFe thin films

Amorphous Tb-Fe thin films prepared by dual magnetron cosputtering were exposed to air at 200 °C in order to investigate the evolution of the films as they oxidize. Magnetic properties of the films were measured using a vibrating-sample magnetometer and torque magnetometer and are interpreted in light of the structure of the films as revealed by Auger electron spectroscopy and composition-depth profiling. This leads to a detailed and self-consistent description of the oxidation process. At first a uniform and homogeneous oxidation layer grows from the surface toward the substrate. This layer has a high magnetization and low intrinsic anisotropy and consists of an intimate mixture of oxidized Tb and metallic TbxFe(1−x). The initially high intrinsic anisotropy of the unoxidized region decreases relatively quickly, while the composition changes only slowly as this region shrinks. When the oxidation layer reaches the substrate, two oxide phases (Fe2O3 and Tb2O3) begin to grow at the surface exposed to air.

非晶質ＴｂＦｅ薄膜を用いた磁気ホログラフィによる高密度記録 ＩＩ

Previously we reported that it is possible to record information by means of magnetic holography (using amorphous TbFe thin films as a hologram medium) onto a spot whose diameter is less than 1 mm and to reconstruct it by using the Faraday effect. However, we had not studied the basic characteristics for information storage in detail, and therefore did not then have a proper way of making good holograms reproducibly. Because reproducibility is the most important characteristic for recording, we studied the recording margin for information storage by magnetic holography. In addition, we discussed the relationship between the power density of two beams (object beam and reference beam) and the domain pattern (hologram). It was confirmed that the domain pattern has a close relation to the beam density, and the recording margin depends on the information pattern. From these results, we can make a good hologram reproducibly.

Intrinsic anisotropy of Tb-Fe films prepared by magnetron Co sputtering

Amorphous Tb-Fe thin films have been produced by dual-gun dc magnetron cosputtering, which allows a moderate range of compositions (spanning about 20 at. %) to be deposited in a single run under identical conditions. The films exhibit clean M-H loops and torque curves which are somewhat anomalous but show consistent trends. Films deposited at room temperature with a composition in the range 17–30 at. % Tb showed a positive intrinsic anisotropy of roughly 3×106 erg/cm3, resulting in an easy axis of magnetization that is perpendicular to the plane of the film, while films with >37 at. % Tb had a small negative intrinsic anisotropy (ca. −2×105 erg/cm3). The temperature dependence of the anisotropy indicates that neither uniaxial stress nor shape anisotropy can account for most of the intrinsic uniaxial anisotropy observed, so we hypothesize that the large anisotropy must be due to pair ordering or a local anisotropy field.

Temperature dependence of the magnetic properties of amorphous TbFe thin films determined from hall effect measurements

Measurements of the extraordinary Hall effect as a function of temperature for amorphous TbFe thin films of various thicknesses and compositions were performed to investigate the thickness dependence of the magnetic properties previously observed for rare earth-transition metal thin films. It is found that a change in the composition alters the temperature dependence of the extraordinary Hall resistivity ρ H( T). The change in ρ H( T) with film thickness is found to be much greater than that which can be ascribed to a change in the composition alone. These experimental results support our previously proposed model that the microstructure-induced variations in the short-range order are the dominant reason for the change in the magnetic properties with film thickness.

Homogeneity studies of amorphous TbFe films by Kerr and Hall effect methods

The homogeneity of amorphous TbFe thin films was examined, utilizing variable phase retardation in polar Kerr effect measurements in conjunction with extraordinary Hall effect studies. These techniques were suggested as very useful tools to study film homogeneity in amorphous rare earth-transition metal thin films with composition close to the compensation composition.

Aging phenomena in TbFe thin films

The aging phenomenon of amorphous TbFe thin films when protected with a SiO2 layer is studied by plotting the hysteresis cycles of the films at various time intervals. The changes observed in the coercive field are related to the changes in the Tb content of the layer. It is suggested that Tb atoms, in spite of their size, can move easily in the layer and tend to migrate out of the amorphous TbFe film. This hypothesis is confirmed by the differences observed in TbFe films deposited on pure Tb underlayers of different thicknesses and by Auger profiles carried out on aged samples.

High-Density Information Storage by Means of Magnetic Holography on Amorphous TbFe Thin Films

High-density information storage by means of magnetic holography is demonstrated by using amorphous TbFe thin films as a magnetic hologram medium. The object beam, which emerges from a two-dimensional information pattern (in most cases 35 mm photographic films), is focused on TbFe film by a lens using the spatial Fourier-transform pattern. A magnetic hologram, that is, a magnetic domain pattern corresponding to the interference pattern of the object beam and the reference beam, is established on the TbFe film by thermo-magnetic writing. A Q-switched ruby laser (of peak light power=0.6MW and light pulse durations30 ns) was used as the writing light source. An illuminated spot, from 0.2 to 1 mm in diameter, was chosen depending on the size of information. Image reconstruction was done by means of either the Faraday effect (transmitted light) or the polar Kerr effect (reflected light) using a first-order diffracted beam. A He-Ne laser (1 mW or 30 mW) was used for the reconstruction light source. It was confirmed that satisfactory images of not only documents but also picture images can be reconstructed by magnetic holography. The storage density estimated from the preliminary experiment is about 4×103 characters/mm2. Some considerations for improving the reconstructed image quality are also described.

Extraordinary Hall resistivity in amorphous terbium–iron thin films and its temperature dependence

Measurements of the extraordinary Hall effect are performed as a function of temperature for amorphous Tb–Fe thin films of compositions close to 21 and 25 at. % Tb. The experimental results indicate that the Fe sublattice gives the dominant contribution to the extraordinary Hall effect.

Thickness dependence of magnetic hysteretic properties of rf-sputtered amorphous Tb–Fe alloy thin films

The variation in the magnetic hysteretic properties of rf-sputtered amorphous Tb–Fe thin films as a function of the nominal film thickness was investigated, using Kerr magneto-optic and Hall effect measurements. The results on the thickness dependence of coercivity, polarity of the hysteresis loop, and Curie temperature of films prepared at the same sputtering condition indicate that there is a change in the ‘‘effective’’ film composition. This composition change is believed to be due to microstructure-induced variations in the short-range order during the film growth.

Sputtering-induced recrystallization on the target and its effect on magnetic properties of amorphous rare-earth transition metal thin films

An investigation was made to evaluate the variation in the magnetic hysteretic properties of rf-sputtered amorphous Tb-Fe thin films as a function of sputtering parameters, such as Ar pressure and rf input power. It was discovered that, during sputtering from a composite target which consists of rare-earth disks placed on a transition metal plate, the average surface composition of the target changed by formation of intermetallic RE-TM compounds through a recrystallization process on the RE disk surface. Using x-ray diffraction, electron microprobe, and scanning electron microscopy, analysis of the surface revealed that the amount and morphology of intermetallic compounds formed had a strong dependence on Ar pressure but a lesser dependence on power. The magnetic properties of the films deposited under different sputtering conditions were measured using Kerr magneto-optic and VSM hysteresis loop tracers. The results show that the changes in the magnitude of magnetization, coercivity, and polarity of the hysteresis loop of the films obtained from a given sputtering target with various sputtering parameters are the consequence of changes in film composition which arise from the altered surface composition and morphology of the sputtering target.

An investigation of amorphous Tb-Fe thin films for magneto-optic memory application

Amorphous Tb <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">x</inf> Fe <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1-x</inf> ( <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.16 &lt; x &lt; 0.35</tex> ) thin films produced by rf co-sputtering have been investigated for magneto-optic memory media application. The anisotropy, hysteresis and coercivity of the films were investigated as a function of composition and film thickness. The sputtered films were overcoated with thermally evaporated SiO. The effect of SiO thickness on the Kerr magneto-optic enhancement and the reflectivity was also measured. It was found that the magnetization and coercivity of those films having perpendicular anisotropy change dramatically not only with target composition but also with film thickness. Thin films having a high hysteresis loop squareness and a coercivity appropriate for magneto-optic recording (500 to 2000 Oe.) were produced from film compositions near the compensation composition of 22.3 at. % Tb. Thermomagnetic writing and reading of the TbFe films were made with a GaAs laser. The results show that the films have a high writing sensitivity (threshold energy of 0.2 nJ and saturation energy of 0.3 nJ) and a high reading contrast for bit sizes of 1 micron.

The microstructure and magnetic properties of amorphous TbFe(O 2) thin films

Amorphous Tb-Fe films were prepared by vapour deposition in ultrahigh vacuum or at partial oxygen pressures in the range 10 −7–10 −3 Pa. In the highly oxygen-doped films we observed the presence of both iron-rich crystallites and terbium oxide. Interpretation of the magnetic domain structure indicates a gradual change in the easy axis of magnetization from perpendicular to in-plane as the oxygen content in the films increases. At the highest oxygen partial pressures we found both a rapid increase of the saturation magnetization and a drop in the Curie temperature and coercive force. The correlation of structural features and magnetic properties is discussed.

Tb-Feアモルファス薄膜による弾性表面波の伝搬速度の変化

Tb-Feアモルファス薄膜による弾性表面波の伝搬速度の変化

Magnetic properties of amorphous Tb-Fe thin films prepared by rf sputtering

The magnetic properties of amorphous TbxFe1−x films prepared by rf cosputtering were studied. For 0.15&amp;lt;x&amp;lt;0.28, the films have uniaxial magnetic anisotropy normal to the film plane sufficient to stabilize cylindrical domains. The Curie temperature Tc and the coercivity Hc were measured as a function of composition. Tc increases monotonically with increasing Tb content in the alloy films in the region 0.1 &amp;lt; x&amp;lt;0.5. Hc is about one order of magnitude large, in contrast with amorphous Gd-Fe films at room temperature, and it increases further at low temperatures. Amorphous Tb-Fe films have a high potential for thermomagnetic recording using the Curie temperature because of the large Hc (1–5 kOe) and the low Curie temperature (∼120°C).