S. Tsunashima

Magnetization Process of Exchange-Coupled Ferrimagnetic Double-Layered Films

Magnetization curves are theoretically calculated for exchange-coupled ferrimagnetic double-layered (ECDL) films, each layer of which has a uniaxial anisotropy with the easy axis perpendicular to the film plane and exhibits a rectangular hysteresis loop. With this model are obtained the conditions for the appearance of anomalous and inverted hysteresis loops observed by the Kerr magneto-optic method. Experiments are made on Gd-Fe/Tb-Fe double-layered films deposited successively in a vacuum better than 10-6 Torr. By comparing the experimental switching field for the Gd-Fe layer in ECDL films with the theory, the energy density of the interface wall is estimated to be 1–2 erg/cm2.

Stress induced anisotropy in amorphous Gd-Fe and Tb-Fe sputtered films

The perpendicular anisotropy caused by the internal planar stress due to the substrate constraint in Gd‐Fe and Tb‐Fe sputtered films was investigated. The internal planar stress σ in these films is found to be very sensitive to preparation conditions, especially to the argon pressure during sputtering, PAr. Stress is compressive for low PAr and tensile for high PAr. The contribution of the stress to the total perpendicular anisotropy varies depending on PAr. Measurement of the anisotropy change before and after the removal of the substrate reveals that the predominant part of the perpendicular anisotropy originates from the internal stress due to the substrate constraint for Tb‐Fe films with a composition of around 30 at.%Tb, where the magnetostriction is extraordinarily large.

Exchange coupling between antiferromagnetic Mn-Ir and ferromagnetic Ni-Fe layers

Exchange couplings between antiferromagnetic Mn–Ir and ferromagnetic Ni–Fe layers have been investigated while varying the Mn–Ir composition. These exchange couplings appeared at room temperature at Ir compositions between 20 and 46 at.%. The maximum exchange coupling field of 3.2 kA/m was obtained for Mn–20 at.%Ir(59 nm)/Ni–Fe(20 nm)/Zr(10 nm). Dependence of the exchange coupling fields on each layer thickness was also investigated. The Mn–Ir/Ni–Fe bilayers maintained high exchange coupling fields at Mn–Ir layer thicknesses above 10 nm.

Perpendicular Magnetic Anisotropy And Magneto-Optical Kerr Spectra Of MBE-Grown PtCo Alloy Films

Pt/sub 50/Co/sub 50/ alloy films have been grown by MBE method onto heated MgO(100) and (111) substrates. It is found that films grown on a (111) substrate at 300/spl deg/C have the CuPt type structure, whereas films grown onto (111) substrate at 500/spl deg/C and onto (100) substrate at 300/spl deg/C and 400/spl deg/C form in the PtCo ordered phase with AuCu structure. The film of the CuPt type exhibits a very large perpendicular magnetic anisotropy of 1.0/spl times/10/sup 6/ J/m/sup 3/, due to the layered structure along the film normal direction. The spectrum of Kerr rotation /spl theta//sub k/ of the film with CuPt structure is considerably different from that of AuCu structure, not exhibiting a maximum around 4.0 eV but showing a peak at 1.4 eV.

Magneto-optical recording

Basic physics and current technologies of magneto-optical recording are reviewed. The development owes much to the discovery of amorphous rare earth-transition metal (RE-TM) films, which exhibit quite uniform magnetic and optical properties in the scale of practical interest. The RE-TM films also exhibit a wide variety of thermomagnetic properties on adjusting their composition, which resulted in the recent development of high-density recording using multilayer films. In amorphous RE-TM films it is possible to record thermomagnetically marks some several tens of nanometres in size. In order to readout such small recorded marks, further development of new readout techniques is necessary.

Magnetoelastic contribution to perpendicular anisotropy in amorphous Gd-Co and Gd-Fe films

The magnetoelastic contribution to the perpendicular anisotropy in rf sputtered amorphous Gd-Co and Gd-Fe films was investigated by the following three experiments: (1) Measurement of the magnetoelastic coupling energy, (2) measurement of the internal planar stress, and (3) the evaluation of the anisotropy due to the substrate constraint. In these experiments it was found that the magnetoelastic contribution to the perpendicular anisotropy is very sensitive to the preparation condition, especially to the substrate bias voltage V b during sputtering. The contribution of the magnetoelastic component to the perpendicular anisotropy is in an order of 104erg/cc, which corresponds to 10∼30% of the total perpendicular anisotropy.

Element-specific imaging of magnetic domains at 25 nm spatial resolution using soft x-ray microscopy

The combination of magnetic circular dichroism as a magnetic contrast mechanism and a transmission x-ray microscope allows imaging of magnetic structures with lateral resolutions down to 25 nm. Results on magneto-optical Tb25(Fe75Co25)75 layers system with thermomagnetically written bits of various sizes were obtained at the x-ray microscope XM-1 at the Advanced Light Source in Berkeley, CA. The results prove the thermal stability of the bits in the recording process. Furthermore the capability of soft x-ray microscopy with respect to the achievable lateral resolution, element specificity and sensitivity to thin magnetic layers is demonstrated. The potential of imaging in applied magnetic fields for both out-of-plane and in-plane magnetized thin magnetic films is outlined.

Giant Magnetoresistance in FeNiCo/Cu Multilayers

The giant magnetoresistance effect of Fe16Ni66Co18/Cu multilayers prepared by the RF magnetron sputtering method is reported. A magnetoresistance ratio as large as 35% is obtained at 300 K, and it oscillates as a function of Cu layer thickness. The oscillation period is about 1 nm, which is similar to the case of Co/Cu multilayers. The maximum interlayer coupling strength for the first peak is about 0.05 erg/cm2. For the second peak the coupling is as weak as 0.003 erg/cm2 with a magnetoresistance ratio of 13%.

Perpendicular Magnetic Anisotropy of TbCo Films

An experimental study has been made on the magnetic anisotropy of amorphous TbCo films prepared by rf co-sputtering. TbCo films prepared at a substrate bias voltage of –100 V exhibit a large uniaxial anisotropy of 2×106 erg/cm3 with its easy axis perpendicular to the film plane, whereas films prepared without the substrate bias exhibit the anisotropy with its easy axis in the film plane. The planar stress due to the substrate constraint considerably influences the perpendicular anisotropy through the large magnetostriction of about 2×10-4. When films with perpendicular anisotropy are removed from the substrate, the anisotropy energy decreases to 65–80 percent of its initial value. Annealing for one hour at 300°C destroys the perpendicular anisotropy almost completely.

Magneto-optical properties of PdCo based multilayered films

The magnetooptical and magnetic properties of multilayered films composed of PdCo alloy and other noble metal (Pd, Pt, or Cu) layers were investigated. Multilayered films were prepared by RF magnetron sputtering. Kerr rotation spectra (275-800 nm) of Pd/Co multilayered films resemble those of PdCo alloys. In the films composed of PdCo alloy and Pt bilayers, the Kerr rotation increases with increasing Pt content while the perpendicular anisotropy decreases. >