Tokutaro Hirone

The Magnetic Properties of FeSex with the NiAs Structure

The thermal and X-ray analyses were carried out for iron-selenium system from 48.8 to 57.4 atomic percent of selenium, such range being previously reported to be ferrimagnetic.It was concluded from the experimental results that at room temperature the concentration range from 48.8 to 53.1% selenium is the two phase region α+β; α has the PbO type structure and β the NiAs type. These two phases transform through a eutectoid reaction into a γ phase with the NiAs structure of slightly different lattice parameters in comparison with those of the β phase, the eutectic temperature being 350°C. The solubility limit in iron side of the phase lies at 53.1% selenium. It is remarkable that the substance with stoichiometric concentration (50% Se) does not lie in the single phase region of NiAs type. It was also found that the ferrimagnetism of this binary system originates from the phase of NiAs type (β phase) and the α phase is weakly paramagnetic or antiferromagnetic.The Curie point of the compound containing 53.1% ...

On the Ferrimagnetism of Iron Selenides

The thermomagnetic properties of iron selenides FeSe x with various selenium contents x were measured as functions of temperature. The thermomagnetic curves obtained belong to the ordinary Weiss type. It was also found that the magnetization at the boiling temperature of liquid nitrogen increases with the selenium content, reaches its maximum value. 35 gauss, at x =1.23, and then decreases again with further increase of x . The Neel temperature was approximately 150°C in the range of x from 1 to 1.26 whereas it decreases gradually with further increase of x and approaches to its lowest value 30°C at x =1.35. The origin of the magnetization of this substance was discussed based on the theory of ferrimagnetism.

On the Magnetocrystalline Anisotropy of Iron Selenide Fe7Se8

Magnetization measurements along the a -and c -axes of a single crystal of a compound Fe 7 Se 8 have been carried out in magnetic fields up to 92 kOe over the temperature range 4.2° to 300°K, together with magnetic torque measurements on the b c -plane up to 9 kOe. The results of magnetization measurements along the c -axis lead to the magnetocrystalline anisotropy energy of the form, E (θ)=- K 0 |cos θ|+ K 3 cos 2 θ+ K 4 cos 4 θ, the last term being for minor correction. In this expression θ is an angle between magnetization and field direction. The measured values of anisotropy constants K 0 and K 3 at 290°, 77° and 4.2°K are K 0 =0.3×10 6 , 32×10 6 and 65×10 6 erg/cc and K 3 =2.5×10 6 , 18×10 6 and 35×10 6 erg/cc, respectively. From the magnetocrystalline energy mentioned above, it can be shown that the magnetic moment takes a conical distribution around the c -axis at low temperatures. The results of torque measurements on the b c -plane is reproduced by assuming a triad crystal domain structure.

On the Magnetic Properties of Nickel-Arsenide Type Crystals

The formation of the ordered arrangement of the magnetic moments of cations (spin ordering or spin arrangement) in the crystal lattice of the nickel-arsenide type is studied theoretically with the molecular field approximation, taking into account interaction between pairs of cations, which form the first, second or third neighbours in the crystal lattice. Various types of spin arrangement in this structure with two kinds of cations are derived. Based on the results obtained the magnetic properties of the compounds are discussed. The theory is applied as a typical example to the interpretation of the magnetism of the ternary solid solution of manganese-chromium-antimony system.

On the Magnetic Properties of the System MnSb-CrSb

The change of magnetic properties due to the replacement of manganese by chromium in manganese antimonide (MnSb), which is of the NiAs structure, was investigated. It was found that, with the increase of the concentration of chromium, the magnetic behaviour of these compounds (Mn 1- x Cr x )Sb changes as follows: (1) at x =0 (MnSb), the temperature-magnetization curve shows typical behaviour of ferromagnetic substance, (2) in the range 0.1≤ x ≤0.7, it deviates remarkably from the Weiss curve in proportion with the chromium content, and the temperature dependence of the reciprocal susceptibility above the Curie point is of a ferrimagnetic type. (3) In the range 0.8≤ x ≤0.9 a transition from ferrimagnetic to antiferromagnetic was observed, and finally (4) at x =1 (CrSb) a typical antiferromagnetism could be seen. A short discussion of such transitions is given.

Diffusion of Nickel in Silver

The diffusion coefficient of nickel in single-crystal of silver has been measured by the lathe-sectioning technique as a function of temperature throughout the range from 750°C to 950°C using radioactive isotope Ni 63 as a tracer. The results are expressed as follows: \begin{aligned} D{=}(21.9)\exp\left(-\frac{54\ 800}{RT}\right)\ \text{cm}^{2}/\text{sec}. \end{aligned} The value of activation energy, 54.8 kcal/mole, obtained by the present experiment is in good agreement with the result of the screening theory of impurity diffusion.

Diffusion of Cobalt into Silver

The diffusion coefficient of cobalt into silver has been measured as a function of temperature over the range from 745°C to 943°C by the tracer and lathe-sectioning technique. It has been found that the diffusion coefficient can be expressed as follows; \begin{aligned} D{=}(104)\exp\frac{59.9}{RT}10^{3}\ \text{cm}^{2}/\text{sec}. \end{aligned} The value of activation energy, 59.9K cal/mol, obtained by the present experiment is in good agreement with the result of the screening theory of impurity diffusion, but considerable discrepancy is found between the observed and theoretical frequency factor. The amount of diffused cobalt showes an abnormal decrease near the diffusing surface, which may be caused by the low solubility limit of cobalt in silver.

The Change of Curie Temperature of Ordered Au4Mn and of Indium Heusler Alloy by Hydrostatic Pressure

The change of the Curie temperature by the application of 3 katm. of hydrostatic pressure to the indium Heusler alloy as well as the intermetallic compound Au 4 Mn was measured. It was found that the rate of change takes positive values, 1.5×10 -3 and 2.7×10 -3 deg/kg/cm 2 for the Heusler alloy and the Au 4 Mn respectively. It was also elucidated that the relative changes of absolute saturation of magnetization for both alloys are negative, -2.1×10 -12 and -7.2×10 -12 cm 2 /dyne respectively.

Megnetocrystalline Anisotropy of Pyrrhotite

Magnetization curves in the base plane and along the c-axis of natural pyrrhotite crystals (Fe 7 S 8 ) are measured up to a magnetic field strength of 90 kOe. The results can be expressed in terms of the magnetocrystalline anisotropy energy, E k =- K 0 |cos θ|+ K 3 cos 2 θ+ K 4 cos 4 θ, the last term being the correction term for the preceding one. The values of K 0 , K 3 and K 4 obtained are K 0 =0.51×10 6 erg/cc, K 3 =3.2×10 6 erg/cc and K 4 =0.098×10 6 erg/cc at 293°K and K 0 =1.2×10 6 erg/cc K 3 =4.2×10 6 erg/cc and K 4 =0.21×10 6 erg/cc at 77°K. These values obtained are discussed on the basis of Adachis theory of magnetocrystalline anisotropy.

Thermal Analysis of Iron Sulfides at the Temperature Range of β-transformation

The measurements of specific heat was performed at the temperature range of β-transformation in iron sulfides with various sulfur contents x ranging from x =1 to x =1.12. A peak in specific heat versus temperature curve is found at 315°C, and this temperature as well as the jump in specific heat, 0.05 cal gr. -1 deg. -1 in value, is almost independent of sulfur contents. The mechanism of transformation is discussed, based upon the theory of ferrimagnetism, and it is concluded that the present experimental results accord well with the theoretical ones.