M. Sahashi

A magnetic thin film inductor and its application to a MHz switching dc-dc converter

The authors propose a novel structured magnetic thin film inductor using rotation magnetization only. The thin film inductor has a sandwich structure, which consists of a double-rectangular spiral coil between top and bottom CoZrNb amorphous thin films. The sputtered CoZrNb amorphous magnetic thin films have uniaxial magnetic anisotropy induced by direct current field annealing. The easy magnetization axis is directed to the main axis of the rectangular spiral coil. Hence, only the rotation magnetization process dominates in this device. The typical specifications are as follows; 3.5/spl times/5.5 mm in size, inductance of 1 /spl mu/H constant up to 10 MHz, and a quality factor of 10 at 10 MHz. A MHz switching chopper dc-dc converter has been developed by using this thin film inductor, bare-chip semiconductor devices (a power MOSFET and a Schottky barrier diode), and a multilayer ceramic capacitor. This converter with a 0.1 cc volume has an output power over 1 W at 5 MHz switching, and the power density exceeds 10 W/cc (160 W/in/sup 3/). >

Mn substitution effect on magnetostriction temperature dependence in Tb0.3Dy0.7Fe2

Magnetostriction temperature dependencies in Tb0.3Dy0.7 (Fe1−xMnx)2 were investigated. Mn substitution lowers the spin reorientation temperature, at which magnetostriction shows a sharp drop. Moreover, Mn containing compounds show larger magnetostriction than that for a Mn‐free compound at low temperature. Mossbauer measurements show that easy magnetization direction for the Mn containing compound is in the 〈111〉 direction at 300 K, while it is in the 〈100〉 at 77 K. These results indicate that the tetragonal distortion λ100 increases by Mn addition in Tb0.3Dy0.7Fe2.

Study of high power planar inductor

A method for planar inductor design has been established on the basis of a discussion of the magnetic flux density distribution. Planar inductors for miniature DC-DC converters have been developed using this design method. This converter is much smaller and thinner than conventional ones, and has an output power/volume ratio of 1.7 W/cc. A spiral coil with a very small distance between the conductors and a low loss magnetic sheet are required for the development of high Q planar inductors. >

New Magnetic Material R3T System With Extremely Large Heat Capacities Used as Heat Regenerators

We developed a new magnetic material R3T system, where R is a rare earth metal and T a transition metal, used as a regenerator matrix in a conventional two-stage Gifford-McMahon (GM) type cryocooler. These compounds, especially Er3Ni (Erbium 3 Nickel), possess extremely large heat capacities between 4 K and room temperature because of their low Debye temperatures, about 150 K, and broadened large peaks in specific heat due to complicated ferromagnetic or antiferromagnetic spin configuraxadtions near each transition temperature, for instance 7 K for Er3Ni.

Specific Heat of a Regenerator Material Er3Ni

Specific heat measurement was performed in the temperature range from 800 mK to 62 K on the regenerator material Er3Ni which is an antiferromagnet with a Neel temperature of 6.1 K and possesses a large volumetric heat capacity even at temperatures above T N. The magnetic contribution to the specific heat has been carefully divided into two parts, one of which is caused by entropy change due to the magnetic ordering and the other a contribution from higher energy level states (Schottky anomaly). The energy levels of the 4f electrons for Er3+ were calculated using the point-charge model, and compared with the experimental data. The entropy change of the Schottky anomaly is large compared with that of magnetic ordering and important for the regenerator material.

A study on the formation of ThMn12 and NaZn13 structures in RFe10Si2

Abstract RFe 10 Si 2 (Rue5fcLa, Pr, Nd, Sm, Gd, Er and Zr compounds were synthesized by the rapid quench method. The ThMn 12 structure can be obtained in the RFe 10 Si 2 system containing Rue5fcSm, Gd and Er, while the NaZn 13 structure can be obtained in the system containing Rue5fcLa, Pr and Nd. It has also been found that Nd 1− x Zr x Fe 10 Si 2 ( x = 0.25, 0.5 and 0.75) crystallized in the ThMn 12 structure. The factors which control the formation of ThMn 12 and NaZn 13 structures in the RFe 10 Si 2 system are discussed with respect to the atomic radius of the rare earth site element.

Magnetic properties and magnetostriction in grain‐oriented (TbxDy1−x)(Fe1−yMny)1.95 compounds

The magnetic properties and magnetostriction in grain‐oriented (TbxDy1−x)(Fe1−yMny)1.95 compounds with 0.3≤x≤0.5, 0≤y≤0.2 prepared by the Bridgman method have been investigated. It is confirmed that the Mn substitution not only lowers the spin reorientation temperature but also enhances λ〈100〉. This large λ〈100〉 is contradictory to the single‐ion model. For Tb0.5Dy0.5 (Fe0.9Mn0.1)1.95 compound, no spin reorientation, which induces the sharp drop in the magnetostriction is seen in the temperature range from 77 to 400 K. In addition, by choosing the appropriate compressive stress, the quite excellent thermal stability and the large magnetostriction of 2000 ppm in the low applied field can be realized in the Tb0.5Dy0.5 (Fe0.9Mn0.1)1.95 compound. These features make Tb0.5Dy0.5 (Fe0.9Mn0.1)1.95 a promising material applicable to the various giant magnetostrictive actuators.

Magnetic field influence on er3ni specific heat

Er3Ni specific heat in 0, 1, 3, and 4.3 T magnetic fields was measured. The specific heat curves for 0 T and 1 T have a single peak due to magnetic phase transition, but those for 3 T and 4.3 T have no peak. Er3Ni specific heat decreases with increasing magnetic field around its ordering temperature, but increases in the higher-temperature region. Using the measured specific heat data, regenerator efficiency and cooling power were calculated to estimate the specific heat reduction influence due to a magnetic field on the Er3Ni regenerator performance. The results show that efficiency and cooling power in the practical leaking magnetic field are almost the same as those in 0 T.

Crystal Field Effects on Thermal and Magnetic Properties of Er3Co

The specific heat and magnetic susceptibility have been measured for Er3Co. The magnetic susceptibility obeys the Curie-Weiss law in the temperature range of 100-300 K with the effective moment µ eff=9.52µ B. A large magnetic specific heat above the Curie temperature of 13 K was found, which is interpreted in terms of the point-charge model. It is revealed that the crystal field and exchange field are of the same order of magnitude and that the electronic thermal excitations contribute to the magnetic specific heat, resulting in a broad Schottky-type contribution. Moreover, magnetocrystalline anisotropy gives rise to the noncollinear spin structure.

Coercive force of Co added Nd-Fe-B based powders prepared by crushing sintered magnets

An anisotropic resin-bonded magnet was prepared by crushing sintered Nd-Fe-B magnets with Co-Al or Co-Ga. The following magnetic properties for the composition of Nd/sub 14.5/Fe/sub 63/Co/sub 16/Ga/sub 1/B/sub 5.5/ were obtained: (BH)/sub max/=114 kJ/m/sup 3/, B/sub r/=0.89 T, and iH/sub c/=810 kA/m. Co addition is shown to play a significant role in improving the magnetic properties of the crushed powder. The surface layer damaged by crushing becomes thinner in the powder containing Co. In the Co-added sintered magnets, the main crack brought about by Vickers indentation is comparatively easy to propagate through the grain boundaries, and microcrack branchings are rarely observed. These mechanical properties are closely related to the thickness of the damaged surface layer. Al or Ga addition to the Nd-Fe-Co-B system is very effective for obtaining a high coercive force of the powder. >