T. Tsushima

Different origin of the perpendicular anisotropy in amorphous Gd-Fe from Gd-Co films

In order to contribute to the investigations of the mechanism of positive K u induced in the amorphous R-T films, a magnetic study was made on the amorphous Gd-Fe and Gd-Co films prepared under various conditions. It is found that the origin of K u in the Gd-Fe films is quite different from that in the Gd-Co ones. In the case of Gd-Co, the positive K u is known to be induced by a resputtering effect and its physical origin is thought as an atomic pair ordering. However, a different mechanism of stress induced anisotropy is taken as the responsible one for the positive K u in the Gd-Fe films.

Anisotropic Distribution of Atomic Pairs Induced by the Preferential Resputtering Effect in Amorphous Gd-Fe and Gd-Co Films

Mossbauer effect and X-ray diffraction of amorphous Gd-Fe films show that isolated Gd atoms are preferentially resputtered and a non-uniform distribution of Gd atoms is induced in amorphous Gd-T (T=3d transition metal) films prepared by a sputtering method with negative bias. The resputtering effect of isolated Gd atoms produces anisotropic distributions of T-T, Gd-T and Gd-Gd pairs in Gd-T films. The difference between the numbers of T-T pairs parallel and normal to the film amounts to 1020~1021 pairs/cm3. This number of T-T pairs is appropriate to account for the oserved anisotropy of amorphus Gd-Co films. It is coucluded that the anisotropic distribution of atomic pairs is the most important origin of the magnetic uniaxial anisotropy induced by bias sputtering.

Magnetic anisotropy distribution near the surface of amorphous ribbons

Magnetic anisotropy in an amorphous ribbon of Fe 40 Ni 40 P 14 B 6 has been studied. Domain structures and the in-plane anisotropy were measured as a function of the depth from the ribbon surface by a powder technique, transmission electron microscopy and a torque method. Groups of fine domains diminish with depth. The maximum in-plane anisotropy exists at the surface and the anisotropy decreases one or two orders in magnitude at the center of the ribbon. The data have an obvious connection with the surface topography of the ribbon that is introduced in the melt and quench process.

Annealing effects on magnetic properties of amorphous GdCo, GdFe, and GdCoMo films

Long term thermal stability of the amorphous R‐T films is a fundamental requirement for the sake of practical use. Detailed experiments of the annealing effects were made on the amorphous GdCo, GdFe, and GdCoMo films prepared by means of the D.C. biased r.f. sputtering technique. It is found that annealing at various temperatures reduces Ku, but it enhances Ms and A in all of the films. Moreover, it is found also that the changing rates of Ms and Ku decrease with the increase of Mo concentration in the amorphous GdCoMo films.

Rotational-type spin reorientation in Nd 1-x Dy x Co 5 and its application to thermomagnetic generator

A rotational-type spin reorientation (SR) phenomenon is found in single crystals of Nd 1-x Dy x Co 5 , and the SR temperatures are controlled by Dy concentration near room temperature. In the SR temperature region an anomaly of a trapezoid shape is observed in specific heat, and it shows the second order nature of this phase transition. A thermomagnetic generator utilizing this phenomenon is invented, where thermal energy is converted directly into electric energy through the magnetic flux change accompanied with the SR. In an ideal case, the maximum energy that can be converted is evaluated as the magnetic anisotropy energy in the SR temperature region.

Resonance Raman scattering in CdIn2S4

Abstract Two types of resonance Raman effects were observed in the spinel-type semiconductor CdIn 2 S 4 : resonant enhancement of the cross section for “forbidden” 1 LO lines and for second order lines, and resonant cancellation of the cross section for E g line of 184 cm −1 at 300 K. The resonant cancellation occurs with incident light of ≈2.3 eV photon energy. A large intensity change of this line in the temperature variation is accounted for by this resonance effect.

Raman Scattering of Trigonal Se and Te at Very High Pressure

The first-order Raman spectra of trigonal Se and Te have been measured under pressure up to the semiconductor-metal transition points at room temperature. In both materials, a prominent pressure effect is found as an anomalous shift of the A 1 mode to low frequency. This softening indicates interference of the interchain bonding with the intrachain covalent bond. Frequency shifts with pressure show deviations from the lattice dynamical homology of Se and Te. The results are interpreted as aspects of the transition to the puckered layer structure of the high-pressure monoclinic phase of Te.

Dominant Contribution of Preferential Resputtering Effect on Perpendicular Uniaxial Anisotopy in Amorphous Gd-Co Films

In order to investigate the physical origin of the perpendicular uniaxial anisotropy ( K u ) in the amorphous Gd–Co films, 4π M s and K u of the films prepared under some sputtering conditions were measured. It is found that K u is induced by the preferential resputtering effect of the amorphous Gd–Co films.

Resonance Raman scattering in ferromagnetic CdCr2S4

Large enhancement of Raman cross section for the phonon lines at 352 and 396 cm-1 was observed below Tc with ∼ 650 nm excitation light, and it is accounted for by a resonance effect related to the “red shifting” C transition in CdCr2S4. While, for 281 cm-1 line resonant cancellation and enhancement effects were observed with different excitation wavelengths. It becomes evident that the anomalous temperature dependence of intensity of the phonon lines depends strongly on the excitation wavelength corresponding to the electronic transitions near the band gap in CdCr2S4.

Hall effect and magnetoresistance in Fe1−xCuxCr2S4

The Hall effect and the magnetoresistance effect are studied in Fe1−xCuxCr2S4. FeCr2S4 is a ferrimagnetic semiconductor and CuCr2S4 is a ferromagnetic metal. The number and the mobility of charge carriers are determined independently. The mobility decreases as the temperature increases toward the Curie temperature. This shows that the anomalous increase in the electrical resistivity around the Curie temperature is caused by the decrease in the mobility by the spin‐disorder scattering. The temperature dependence of the number of charge carriers indicates that this system is still in a semiconductor state at x=0.65. The negative magnetoresistance effect is observed below the Curie temperature, and is discussed in terms of the spin‐disorder scattering. The compositional dependences of the magnetoresistance effect and the Curie temperature suggest the semiconductive‐to‐metallic transition near x=0.85.