On the Magnetocrystalline Anisotropy of Iron Selenide Fe₇Se₈

Abstract

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.