On the Magnetic Anisotropy of Single Crystal of Mn_5Ge_3

The magnetic anisotropy of a single crystal of Mn_5Ge_3 is measured by means of a torque magnetometer. The direction of easy magnetization is found to lie along the c-axis between room and liquid nitrogen temperatures. The anisotropy constants are determined as 3.0×10^5erg/cm^3 at room temperature and 4.2×10^6 erg/cm^3 at liquid nitrogen temperature. The anisotropy constant determined from magnetization curves at liquid nitrogen temperature is 3.5×10^6erg/cm^3, and agrees well with that from torque measurements. Calculation shows that magnetic dipolar interaction accounts for about 20% of the observed value of the anisotropy. Temperature dependence of the dipolar anisotropy is discussed using molecular field approximation

Magnetocrystalline Anisotropy of Pyrrhotite

Magentization curves in the base plane and along the c-axis of natural pyrrhotite crystals (Fe_7S_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^2θ+K_4cos^4θ, 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=0.51×10^6erg/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 Adachi\u27s theory of magnetocrystalline anisotropy

On the Magnetocrystalline Anisotropy of Iron Selenide Fe_7Se_8

Magnetization measurements along the α- and c-axes of a single crystal of a compound Fe_7Se_8 have been carried out in magnetic fields up to 92 kOe over the temperature range from 4.2° to 300°K, together with magnetic torque measurements on the bc-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|cosθ|+K_3 cos^2θ+K_4 cos^4θ, 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 bc-plane is reproduced by assuming a triad crystal domain structure

Behaviors of Some Magnetic Compounds under Intense Magnetic Fields

Effects of intense magnetic field on the properties of magnetic ions are discussed briefly. Details of the researches on the magnetic properties of some compounds under intense magnetic field are presented. In Fe_7S_8, orbital angular momentum is not quenched and the direction of the magnetic spin is inclined to the basal plane of a pseudo-hexagonal lattice. Magnetic anisotropy energy of Fe_7S_8 is deduced from the magnetization curve under the intense field as high as 100 kOe. In Au_2Mn a transition from antiferromagnetic helical spin structure to a ferromagnetic is observed and the induced magnetostriction is measured. In α-Fe_2O_3 Single crystal, a magnetic field-induced transition from an antiferromagnetic to a weak ferromagnetic and then to the antiferromagnetic is observed. The results of measurements are analyzed on the basis of magneto-crystalline coupling in a rhombohedral lattice. In the compound MnHg, a gradual change of susceptibility is observed at 200°K. This change is accompanied with a deformation of lattice and can not be regarded as a Neel point, based on the measurements of high field susceptibility and specific heat. In Cr-modified Mn_2Sb, the variation of transition point from antiferromagnetic to ferrimagnetic state with magnetic field is observed. A mechanism of the transition is proposed on the basis of a temperature dependent variation of the molecular field coefficient, and the exerimental results are analyzed