T. Kamimori

Heating of ferrite powder by an AC magnetic field for local hyperthermia

To develop materials for achieving local hyperthermia, we investigate the heating of various ferrite and metal powders by applying an external AC magnetic field. In comparison with magnetite powder, which has often been used in previous experiments, Mg-ferrite powder is more applicable for achieving local hyperthermia.

Magnetic properties and exchange interactions in (GdxFe1-x)80Si12B8 amorphous alloys

Abstract Magnetization Curie temperature and magnetovolume effects of amorphous (Gd x Fe 1- x ) 80 Si 12 B 8 alloys (0.1 ⩽ x ⩽ 1.0) were investigated. Gd 80 Si 12 B 8 is an asperomagnet having the Curie temperature of 129 K. The large susceptibility of the asperomagnet enhances the forced volume magnetostriction for x more than 0.7, which reaches about 100 × 10 -10 Oe -1 at x = 1.0 and T = 30 K. The Mossbauer study revealed a decrease of the Fe magnetic moment with an increase of Gd content. Exchange interactions J FeFe and J FeGd evaluated by the fitting of σ - T curves are discussed and compared with those of crystalline GdFe compounds.

Magnetocrystalline Anisotropy in Quenched and Annealed Fe3Si

Magnetocrystalline anisotropy constant K 1 of Fe 1- x Si x (0.08≤ x ≤0.25) in both as-quenched and after-annealed samples was determined from torque measurements in 77∼300 K, in order to make clear the difference in K 1 between disorder and order phase (D0 3 type) of Fe 3 Si at x =0.25. The difference in K 1 between both the cases began to appear at x ≃0.17, and values of K 1 for x =0.25 were determined to be - 1.01× and 0.94×10 5 erg/cm 3 at 77 K in the as-quenched and the after-annealed, respectively. This difference in K 1 was apparently due to the one in the degree of order in D0 3 ; the former value was thought to be of nearly perfect disorder in long range and the latter of perfect order. In any case, it was concluded that K 1 of Fe 3 Si is negative in disorder and positive in order (D0 3 ).

Thickness dependence of field induced uniaxial anisotropy in 80-permalloy films

Abstract The induced uniaxial anisotropy constant, Ku, and the saturation magnetization, Ms, in 80-Permalloy films were examined as a function of thickness by a method involving the magnetoresisttance effect. The films were evaporated in a magnetic field. In contrast to Ms which was independent of thickness, Ku decreased continuosly with decreasing thickness and vanished around 100 A. The value of Ku, however, showed large scatter in films of the same thickness. These facts are well explained in terms of dead and induced anisotropy layers. The dead layer is formed at an initial stage of evaporation and the reason why the anisotropy is not induced is discussed in connection with island structure.

Inhomogeneous Concentration Distribution in Obliquely Evaporated Fe–Cu Films

A distribution of atoms or local concentration in FexCu1-x films prepared by an oblique incident beam is discussed based on the results of the magnetization, Mossbauer effect, X-ray diffraction and simulation of a film-formation process. From these experiments, it was concluded that an inhomogeneous concentration distribution takes place in a column which is formed by oblique incidence. In each column three kinds of regions (Fe, Fe-Cu and Cu) are found, depending on the iron contents (x) and the incidence angles (θ). When θ is small, only an Fe-Cu region appears; this is an Fe-rich (bcc) or Cu-rich (fcc) alloy corresponding to large or small x, respectively. When θ is large, Fe and Cu regions appear instead of Fe-Cu regions; also, x affects the volume ratio of the Fe to Cu regions.

Reentrant spin glass behavior of FeY amorphous alloys

Abstract AC susceptibility, magnetization and Mossbauer spectra have been measured for Fe100−xYx (x = 20−60 at%) amorphous alloys made by melt-spinning method. The results show a reentrant spin glass. This state is intermediate between ferromagnetic and spin glass states for a-FeY alloys made by melt-spinning and sputtering methods, respectively. Three states above are discussed with the change of atomic disorder depending on the quenching speed.

Preferential site occupation of M atoms and the Curie temperature in Y2Fe17-xMx (M = Al, Si, Ga)

Abstract The Curie temperature, lattice parameters and the 57 Fe Mossbauer spectra were studied on Y 2 Fe 17- x M x , where M = Al(0 ⩽ x ⩽ 4), Si(0 ⩽ x ⩽ 3.5) and Ga(0 ⩽ x ⩽ 11). The analysis of Mossbauer spectrum shows the preferential site occupation of M atoms. The preference has little dependence on M. The behavior of the Curie temperature is closely related not to the lattice dimension but to the preferential site occupation of M.

Pressure Effects Estimated from Forced Volume Magnetostriction for Ni–Tm [Tm=Ti, V, Cr, Mn] Alloys

The temperature dependence of forced volume magnetostriction dω/d H for Ni 1- x Ti x ( x ≤0.1) and Ni 1- x V x ( x ≤0.08) alloys has been measured using the 3-terminal capacitance method. The values of dω/d H for Ni ∼8 at%Ti-Ni and ∼6 at%V-Ni alloys change their sign from positive to negative with raising the temperature. Pressure coefficients, d ln µ/d p and d ln T c /d p , have been deduced from the temperature dependence of dω/d H using the thermodynamical and the Kornetzki-Kouvel relations. The relation between two pressure coefficients above are analysed according to Inoue and Shimizus discussion. The values of the coefficient C /χ hf T c obtained decrease gradually from 2 to 1 with decreasing T c toward 0 K for both alloy systems.

The Magnetovolume Effect of an Amorphous Magnet Gd67Ni33

We have observed a large magnetovolume effect in a melt spun Gd-rich amorphous magnet Gd 67 Ni 33 . The magnet shows the forced volume magnetostriction of a positive value of 3.76×10 -5 T -1 at 4.4...

Site occupancy of Fe atom and magnetic phases of GdFe4+xAl8−x (0 ≦ x ≦ 2)

Abstract From the Mossbauer and a.c. magnetic susceptibility studies of GdFe4+xAl8−x compounds (0 ≦ x ≦ 2) the concentration dependence of site occupancy of Fe atom and the concentration-temperature magnetic phase diagram are presented. The former plays an important role in the latter.