Y. Sakurai

Magnetic Anisotropy and Magneto-Optical Properties of Iron Oxide Films

Iron oxide films were prepared by rf diode sputtering. Magnetic and magneto-optical properties of the iron oxide films are discussed. Perpendicular anisotropy was induced in sputtered iron oxide films (typically Ku=2×105 erg/cm3). This perpendicular anisotropy was lost by annealing in air. The value of the Faraday constant θf was typically 2×104 deg/cm at 633 nm. The absorption coefficient α was 105 cm-1 at 0.4-2.4 µm.

Sublattice contributions on Faraday rotation in annealed {YBi}3[Fe2−xGax](Fe3−yGay)O12

Sublattice contributions on the Faraday rotation were studied in BiGa:YIG films in which the sublattice moments were modified through an intersite migration of nonmagnetic Ga3+ by annealing. Linear combination of a- and d-site moments on the rotation was observed with a deviation of less than 0.5%. a-site Fe3+ had larger influence on the rotation although it seemed to depend on the Bi concentration.

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.

Magnetic Properties of SmCo Sputter-Deposited Polycrystalline Films

SmCo polycrystalline films were sputter-formed on glass substrates at temperatures between 200 and 300°C, and relations between precipitated phases and film magnetic properties were studied. Phases with Sm-Co stoichiometric ratios of 2-17, 1-5, 1-3, and 1-2 were tentatively identified; these phases exhibit widely varying coercivities, in the ranges of several hundred Oe, several kOe, around 10 kOe, and under 100 Oe, respectively. Except SmCo2, all other phases, which were of hexagonal structure, resulted in a large negative Ku value for the film.

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<inf>r</inf> and H<inf>c</inf> 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<inf>c</inf> increases significantly. At three layers M<inf>r</inf> becomes 300 G, a very high value compared with single-layer films. Though K<inf>u</inf> decreases monotonically with increase in lamination and H<inf>k</inf> = 2K<inf>¿</inf>/M<inf>s</inf> decreases too, H<inf>C</inf> increases resulting in high remanence.

Iron Oxide Sputtered Films with Perpendicular Anisotropy

Perpendicular magnetized sputtered iron oxide film was fabricated. At a substrate temperature of 205°C, the sputtered film was in-plane magnetized, but perpendicular magnetic anisotropy was induced at 176°C. A perpendicular magnetized film was obtained at an oxygen partial pressure of 0.18mTorr over a rather wide substrate temperature range. In the x-ray diffraction pattern there were several unclear Fe3O4 and Fe2O3 peaks which could not be precisely determined.

Laser Writing on Amorphous TbFe Films for Magnetic Printing

The laser (thermal) writing characteristics of amorphous TbFe perpendicular magnetic films of thicknesses h between 0.1 and 3 ¿m are reported. The Ms-Hc characteristics for Tb-rich and Fe-rich films were investigated; for limited film thicknesses h, Tb-rich films, with a larger magnetization, were more suitable for magnetic printing. The write power versus written reverse domain diameter was measured, and it was found that the reverse domain diameter increased geometrically with radiation power for thin (0.1 ¿m) film, but increased linearly for thicker (2.3 ¿m) film. Tb-rich film necessitates greater recording powers, and enables recording over a wide range of Ms·h values.

SmCo Magnetic Films Sputter-Deposited on Heated Substrates

Introduction SmCo in-plain magnetic polycrystalline films of high coercive force are being made on heated substrates [1]. We reported that we were able to obtain amorphous SmCo perpendicular magnetization films through sputtering [2]. In the making of SmCo perpendicular magnetization film, the substrate temperature (one film preparation parameter) has a great effect on the occurrence of perpendicular anisotropy. Perpendicular magnetization film has been obtained (in experiments up to 100°C) by applying substrate bias voltage at temperatures above 800C. This time we studied changes in the films characteristics using substrate heating only.

Sm Addition to GdCo and TbFe Films for Magneto-Optical Memory

Introduction In order to improve the magnetic properties of rare earthtransition metal alloys being studied for magneto-optical memory media, we added Sm to GdTbFeCo (a quaternary alloy), to make a quinternary alloy. We already reported that both the Kerr rotation angle and the magnetic anisotropy increase with the addition of Sm [1]. In order to study the origin of these improvements, we added Sm to GdCo and TbFe (each a binary alloy) to make ternary alloys. We then investigated their magnetic and magneto-optical properties.

Properties of Compositionally Modulated Magnetic Films

Compositionally modulated Gd + Co, Fe70Co30 + SiO2, and Fe + SiO2 films by magnetron RF sputtering were prepared, and the composition depth profiles, electrical and magnetic properties measured. The substrate was rotated during film growth, and the rotation rate converted into an equivalent film deposition time T. Compositional modulation of Gd + Co film down to a period of about 120 Å was confirmed. Short times T resulted in amorphous films of uniform composition in the depth direction, while longer T yielded crystalline film with a sinusoidal demodulated composition profile. The Hc of such film was decreased to 1/10, suggesting a means for obtaining soft magnetic properties.