Magnetization Study of Itinerant-Electron Ferromagnet Y₉Co₇

Abstract

Magnetic-superconductor Y₉Co₇ has been investigated from a magnetization measurement in the temperature range between 0.5 K and 420 K and in the magnetic fields H from ∼2 Oe to 70 kOe. The magnetization M can be expressed in a form of H⁄M=a+bM²+cM⁴ up to 70 kOe at 0.5 K. Above 2.2 K (superconducting transition temperature) and in a limited region of magnetization, the magnetization is expressed in a form of H⁄M=a+bM². The spontaneous magnetization M_s varies with temperature T as M_s²∝(T_m^4⁄3−T^4⁄3), where T_m is the ferromagnetic transition temperature of 4.2 K. The magnetic moment extrapolated to zero temperature and zero field is 0.09 μ_B/Y₉Co₇. These behaviors indicate Y₉Co₇ to be a very weak itinerant-electron ferromagnet. The magnetization curve in a superconducting state suggests a very hard type II superconductor or an inhomogeneous state.