Coexistence of spin glass and superparamagnetism with ferrimagnetic order in polycrystalline spinel Co_0.2Zn_0.8Fe_1.95Ho_0.05O₄

Abstract

We discuss our investigation of DC magnetization, as a function of time, temperature and magnetic field, and explore some distinct magnetic behaviour in the polycrystalline spinel Co_0.2Zn_0.8Fe_1.95Ho_0.05O₄. The system is essentially to be a ferrimagnet and the ferrimagnetic order (spontaneous magnetization) is identified using Arrot plot of M(H) data. Application of some scaling laws have shown the coexistence of spin glass (SG) and superparamagnetism (SPM) with ferrimagnetic order (FIMO) at low and high temperature, respectively, in the system. The coexistence of SG and SPM with FIMO shows paramagnetic to ferrimagnetic state at T_c ≈ 225K and ferrimagnetic to cluster spin glass state below T_m ≈ 120K. The non-linear increase, without hysteresis, of M(H) data above T_C indicates the existence of short range interacting clusters in the paramagnetic state. In addition, the anisotropy effect of Ho³⁺ has shown some interesting magnetic features, such as, spin glass of Ising nature and an unusual maximum in the thermoremanent magnetization about 180 K.