Noriaki Kazama

Effect of silicon addition on the magnetic properties of Fe‐B‐C amorphous alloys

The effect of compositions on the saturation magnetization, Curie temperature and coercivity of the amorphous Fe‐B‐C alloys has been investigated in a wide range of B and C concentration. The C addition less than 7 at.% to Fe‐B alloys increases the saturation magnetization at the room temperature. The highest magnetization, σs = 178 emu/g, with the lowest coercive force, Hc = 22 mOe, has been obtained for the Fe81B12‐C7 alloy annealed in a magnetic field. In order to obtain further desirable soft magnetic properties, the effect of the addition of other elements to the Fe‐B‐C based amorphous alloys has been studied. The best properties are σs (R.T.)  = 176 emu/g, Hc = 8 mOe, Br/B100 = 0.88 and the core loss W/f = 8×10−4 watt. sec/kg (at 12.5 kG and 50 Hz) for the magnetically annealed Fe81B13C2Si4 alloy. As a result, it has been found that the addition of Si is most effective in reducing the coercive force and core loss as well as an improving the magnetic stability during aging at low temperatures.

Metastable Fe nitrides with high Bs prepared by reactive sputtering

Preparation of thick films or bulk formed materials of Fe16N2 compound has been attempted using a high rate reactive‐sputtering technique. As for the reactive gas, N2 was introduced with various pressures (PN2) into the chamber by mixing with Ar gas of about 10−2 Torr. About 0.5‐mm thick bulk deposits were obtained through the continuous running with a 1000 A/min rate. It has been found that the magnetization (σs) of about 240 emu/g exceeding the value for Fe can be obtained around PN2=0.1∼1×10−3 Torr. From thermomagnetization and x‐ray analyses the increased σs is attributed to Fe16N2 compound, but the coexistence of bcc Fe and Fe4N prevents reaching the σs to the expected maximum value 298 emu/g of Fe16N2. From the application point of view, the presently obtained Fe nitrides are interesting in their coercivities and are useful for semihard magnets with high Vicker’s hardness (about 700 Hv).

Magnetic Properties of Cr1-xMnx As System

Studies on X-ray crystallographic, magnetic, neutron diffraction and transport properties have been made of the system Cr 1- x Mn x As (0≤ x ≤0.9). All the members of the system undergo a transition from MnP structure to NiAs structure. Magnetic measurements have revealed the existence of three distinct magnetic regions and the magnetic structures of these regions have been found from neutron diffraction measurements. On the basis of these experimental data, magnetic and crystallographic phase diagrams have been constructed. In particular, CrAs exhibits a discontinuous change in the lattice constants at the Neel temperature which was obtained to be 265°K. The electrical resistivity and thermoelectric power show a strong anomaly at the temperature where the magnetic order disappears. The observed helical spin arrangement may be stabilized by the distorion of the Fermi surface which is caused by the formation of a new zone boundary.

Magnetostriction of Co‐base amorphous alloys and high frequency permeability in their sputtered thin films (invited)

For new magnetic materials with high permeability at MHz frequencies as well as high magnetic induction, magnetic properties of Co‐base amorphous alloys produced by a sputtering technique were investigated. Small magnetostrictions, important for this purpose, were found in the Co‐Nb‐Ti system and Co‐(Fe, Mn)‐Nb system. The dipole‐type model explained the concentration dependence of magnetostriction. In order to increase permeability at high frequencies by reducing eddy current losses, these amorphous alloys were made into thin film form. It was found that dc coercivity for the single film (about 3 μm thick) of Co80 Nb20 with negative magnetostriction was larger than that for Co80Ti20 with positive magnetostriction, while the layered films of Co80Nb20 separated by a SiO2 insulator showed small coercivities. Permeabilities of about 4×103 at 1 MHz and 1×103 at 10 MHz were obtained in the Co80Nb20/SiO2 and Co80Ti20/SiO2 layered films.

Electronic State of High Spin MnAs

The electronic state of high spin MnAs was investigated by using the polarized neutron technique. The experimental results are summarized as follows: i) By analyzing the asphericity of the magnetic form factor with the free ion model, the numbers of electrons in the atomic levels are determined to be (1.0↑+0.3↓, 2.0↑, 0.7↑) for (ψ x 0 , ψ x ± , ψ u ± ) atomic levels, respectively. Therefore, Mn atoms are in the 3d 4 electronic state in MnAs. ii) This electron configuration is convenient to explain the observed metallic conductivity. iii) The spin density distribution shows the characteristics of the above mentioned electron configuration and the strong covalency with the anion As. iv) Spherical part of the magnetic form factor agrees with the calculated one for Mn + , not for Mn 3+ . But this does not imply the Mn atom is in the Mn + state.

Effects of metalloids on the magnetic properties of iron-and cobalt-based amorphous alloys

Abstract Effects of the metalloids on the magnetic properties of Fe- and Co-based amorphous alloys have been observed as a function of the atomic size of these metalloids. The substitution of C by Si in the amorphous Fe81B13C6 resulted in a further reduction of core loss associated with improved thermal stability.

High Spin-Low Spin Transition in MnAs1-xPx(x=0.075)

Some of the physical properties of the compound MnAs 1- x P x ( x =0.075) are investigated by the various measurements, and they can be divided into four different temperature ranges. The compound is: i) for T > T 2 , a high spin state paramagnet with the NiAs type ( B 8 1 ), ii) for T 1 < T < T 2 , a high spin state paramagnet with the MnP type ( B 31), iii) for T N < T < T 1 , an intermediate spin state paramagnet with the MnP type and iv) for T < T N , a low spin state antiferromagnet with the MnP type. Especially in the region iii), an interesting phenomenon of a high spin-low spin transition is observed, and characterized by a large change in the lattice constants and the electrical resistivity.

Magnetic and thermal expansion properties in hydrided Fe–Zr amorphous alloys

The effect of hydrogenation on the Invar‐like thermal expansion anomaly for Fe–Zr amorphous alloys has been investigated. Low temperature magnetization hysteresis has also been examined for the hydrided alloys. The Invar anomaly is changed slightly by hydrogenation only through the increase in the saturation magnetization at 0 K (Mso), since the spontaneous‐volume‐magnetostriction (ωm) for the anomaly increases in proportion to the square of the saturation magnetization (Ms)2. But, the coupling constant between ωm and M2s is not changed by hydrogenation. Field cooling down to 4.2 K makes the magnetization hysteresis asymmetric in the case of the nonhydrided alloys, while no longer any asymmetrical loop has been observed in the hydrided alloys. Thus, the observed large ωm is explained by the simple ferromagnetic effect, rather than by the concept based on a magnetically mixed state.

Electronic State of Low Spin MnAs(P)

The electronic state of the compound MnAs 1- x P x ( x =0.075) was investigated. It is in the low spin state below the Neel temperature (232 K), which is stabilized by the substitution of phosphorus in MnAs for arsenic. By analyzing the neutron magnetic scattering, the following results were obtained: (i) The magnetic structure is a double spiral structure with the propagation vector q =0.111× a * , and the magnetic moment is 1.80±0.05µ B at 78 K . (ii) By analyzing the anisotropy of the magnetic form factor, 3d electron configuration was determined as (1↑+1↓, 2↑, 0) for (ψ x 0 , ψ x ± , ψ u ± ) orbitals. (iii) This configuration explains qualitatively various changes in the physical properties occurring with the high spin-low spin transition. (iv) The radial distribution of 3d electron in the low spin state is more spread than that in the high spin state.

Magnetic Structure of CrAs and Mn‐Substituted CrAs

A neutron diffraction study has been made of powdered samples of CrAs and Mn‐substituted CrAs, namely, Cr0.7Mn0.3As, Cr0.4Mn0.6As, and Cr0.3Mn0.7As. Although CrAs shows a kink in susceptibility at 796°K, the anomaly was found to be due to a crystallographic transformation, from MnP‐type structure (low‐temperature side) to NiAs type. The liquid‐nitrogen temperature diffraction pattern contains a number of magnetic peaks. An analysis of the data gives a double‐layered helical structure, with the propagation vector along the c axis (the space group Pnma), like that found in MnP. The Neel temperature as determined from the temperature dependence of (101)− intensity is about 280°K. The magnetic structure of Cr0.7Mn0.3As is much the same as that of CrAs, but with the Neel temperature at 263°K. Cr0.4Mn0.6As is ferromagnetic with a Curie temperature at 160°K, and has a magnetic transition in the paramagnetic range, which separates the low‐temperature low‐spin state from the high‐temperature intermediate‐spin stat...