Static magnetic response of clusters in Co_{0.2}Zn_{0.8}Fe_{1.95}Ho_{0.05}O_{4} spinel oxide

Earlier investigation of Co_{0.2}Zn_{0.8}Fe_{1.95}Ho_{0.05}O_{4} spinel has shown the existence of "super-ferromagnetic " clusters containing Fe^{3+} and Ho^{3+} ions along with small size clusters of Fe^{3+} ions (Bhowmik et al, J. Magn. Magn. Mater. {247}, 83 (2002)). Here, We report the static magnetic response of these clusters. The experimental data suggests some interesting magnetic features, such as, enhancement of magnetization; re-entrant magnetic transitions with paramagnetic to ferromagnetic state below 225 K and ferromagnetic to spin glass state below 120 K; appearance of field induced ferromagnetism. We also observe an unusual maximum in the thermoremanent magnetization (TRM) vs temperature data. Our measurements suggest that this unusuality in TRM is related to the blocking of "super-ferromagnetic" clusters ,out of the ferromagnetic state, along their local anisotropy axis.