Toshihiko Tokunaga

Frequency dispersion and temperature variation of complex permeability of Ni‐Zn ferrite composite materials

Permeability spectra in Ni‐Zn ferrite composite materials were studied at the volume loading of ferrite above 30% and at temperatures from 100 to 400 K. The permeability decreased with decreases in the volume loading of ferrite. This decrease was much larger than that expected from the empirical mixing law. This was attributed to the demagnetizing field, generated by the magnetic poles on the surface of the ferrite particles. Simultaneously, the demagnetizing field increased spin resonance frequency. For the sintered ferrite, the primary peak of the permeability was just below the Curie temperature. The peak becomes obscure and disappeared as the volume loading decreased. The temperature dependence of the spin resonance frequency was lower in the ferrite composite material than that in the sintered ferrite. These features were also discussed from the view point of the demagnetizing field.

Magnetocrystalline anisotropy and magnetostriction of Pd-Co alloys

Abstract Magnetocrystalline anisotropy and magnetorestriction have been studied for fcc Pd-Co alloys. There is a difference in the concentration dependences between the two regions divided near 50 at% Pd where the hyperfine field changes the sign. In the Co-rich region, they are gentle, while they are steep in the Pd-rich region accompanying the maxima around 15–20 at % Co.

Magnetic and electrical properties of R7Rh3 (R=Gd, Tb, Dy, Ho, Er and Y)

The electric resistivity and magnetic susceptibility have been measured for hexagonal intermetallic compounds R 7 Rh 3 (R=Gd, Tb, Dy, Ho, Er and Y). At low temperature, these compounds except Y 7 Rh 3 have antiferromagnetic order. In room temperature region, the electric resistivity increases with decreasing temperature in all the compounds and some of these compounds show a broad maximum at paramagnetic region. The pronounced increase of electric resistivity due to superzone gap formation at the Fermi level has been observed at the Neel temperature. These properties could be explained by the semimetallic band scheme.

Temperature Dependence of the Forced Magnetostriction of Nickel

Forced longitudinal and transverse magnetostrictions for polycrystalline Ni have been measured by strain gauge technique at temperatures from 200 to 613°K below the Curie point. Results obtained show clearly an anisotropy, so that the forced volume magnetostriction is turned out not to be equal to three times as large as the forced longitudinal magnetstriction. The temperature dependence of the forced volume magnetostriction obtained reliably shows to be positive below \(T/T_{c}{\cong}0.7\) and negative above it. The forced volume magnetostriction at 0°K, (∂ω/∂ H ) 0 =1.4×10 -10 Oe -1 , and the change of the Curie point with pressure, ∂ T c /∂ p =3.2×10 -4 deg/bar, are estimated thermodynamically and agree with Kondorskys results and with Patricks, respectively. A special attension is given to an anomalous thermal expansion near the Curie point.

Magnetostriction of Pd-Co Alloys

Magnetostriction constants h 1 and h 2 of Pd-Co alloys containing 5∼60 at%Co have been measured in the temperature range between 77 K and 300 K. The values of h 1 and h 2 at 0 K determined by the extrapolation increase in magnitude with increasing Co concentration, and reach the maxima of about -3.1 ×10 -4 and -2.9 ×10 -4 at about 15 at%Co, respectively. With further increase of Co, h 1 decreases rapidly in magnitude and becomes positive above about 40 at%Co, while h 2 decreases gradually without change in sign.

Magnetic Anisotropy of Pd-Rich Pd–Co, –Ni and –Fe Alloys

The magnetic anisotropy of Pd-rich Pd–Co, –Ni and –Fe alloys has been measured by the torque method. In Pd–Co alloys, the anisotropy constant K 1 at 4.2 K has negative sign, and has a large maximum value of 1.7×10 6 erg/cm 3 at about 10 at%Co. In Pd–Ni alloys, K 1 has positive sign, and decreases monotonically with decreasing Ni content. In contrast to these alloys, K 1 is vanishingly small for Pd–Fe alloys.

Magnetic Properties of the Amorphous Alloy System (Fe1-xNix)77Si10B13

The saturation magnetic moment µs, the Curie temperature Tc, and the high temperature susceptibility were measured in the amorphous alloy system (Fe1-xNix)77Si10B13. The measurements were done for temperatures above 77 K. The variation of µs and Tc with x were similar to that in other (Fe-Ni)-amorphous systems so far reported. The susceptibility was measured for specimens with 0.6x1.0. Ni77Si10B13 or x=1.0 was found to have Pauli type paramagnetism with χg=2×10-6 emu/g over the temperature range 77-500 K. The susceptibilities for other specimens followed the Curie-Weiss law well, and so the Curie constant Cg, the effective magnetic moment µeff, and the asymptotic Curie temperature Θ were determined. Cg, µeff, and Θ decreased so as to vanish at x~1.0.

Magnetic Properties of the (Fe1-xMx)3P Compounds

The crystal structure, magnetic transition point and saturation magnetic moment were determined for (Fe1-xMx)3P compounds with M=Cr, Mn, Co, Ni. X-ray examination identified all the compounds as b.c.t., except Mn compounds with 0.3 0.3 could not be prepared. Antiferromagnetism was found in Mn compounds with x>0.3. The concentration dependence of lattice constants indicates that, in the range of small x, the substitution occurs preferentially at a specified site. The saturation moment at 4.2 K decreases almost linearly with increasing x, but with a different slope depending on the substituted elements. The result was discussed based on the assumption of the preferential substitution.

Magnetic and electrical properties of the intermetallic compounds R7Rh3 (R=La, Ce, Pr and Nd)

Abstract Magnetic and electrical properties of the hexagonal Th 7 Fe 3 -type R 7 Rh 3 compounds (R=La, Ce, Pr and Nd) have been studied by measuring a.c. magnetic susceptibility, magnetization, electrical resistivity, thermoelectric power and thermal expansion for polycrystalline samples. The Ce 7 Rh 3 and Pr 7 Rh 3 show ferromagnetic ordering below 6.8 and 15.6 K, respectively. In Nd 7 Rh 3 , there are two magnetic ordered phases; the ferromagnetic phase below 11 K and the antiferromagnetic phase up to 32 K. In the antiferromagnetic phase, a metamagnetic transition takes place. Pronounced changes at the magnetic transitions are observed in thermoelectric power.

Magnetocrystalline Anisotropy of Ni-Pd Alloys

The magnetocrystalline anisotropy constants of disordered Ni-Pd alloys containing 20, 30, 40, 50, 60, 75 and 90 at% Pd have been studied in a range from 4.2 K up to the Curie temperature T c by the use of the torque method. At 0 K, the first anisotropy constant K 1 of 20% Pd is much the same as that of Ni. Then K 1 varies rapidly accompanying a change in sign from negative to positive at 50% Pd and takes the maximum at about 65% Pd. The higher order constants K 2 and K 3 show a complicated dependence on the content of Pd. As temperature is raised, K 1 of the alloys with negative K 1 at 0 K changes the sign likewise Ni and the reduced temperature T / T c where the sign changes, lowers as Pd increases. For the alloys with positive one, it decreases monotonically. Discussions are qualitatively made on K 1 .