Magnetic compensation, field-dependent magnetization reversal, and complex magnetic ordering in Co2TiO4

Abstract

The complex nature of magnetic ordering in the spinel Co2TiO4 is investigated by analyzing the temperature and magnetic field dependence of its magnetization (M), specific heat (Cp), and ac magnetic susceptibilities χ′ and χ″. X-ray diffraction of the sample synthesized by the solid-state reaction route confirmed the spinel structure whereas x-ray photoelectron spectroscopy shows its electronic structure to be Co2TiO4=[Co2+][Co3+Ti3+]O4. From analysis of the temperature dependence of the dc paramagnetic susceptibility, the magnetic moments μ(A)=3.87μB and μ(B)=5.19μB on the A and B sites are determined with μ(B) in turn yielding μ(Ti3+)=1.73μB and μ(Co3+)=4.89μB. Analysis of the dc and ac susceptibilities combined with the weak anomalies observed in the Cp vs T data shows the existence of a quasi-long-range ferrimagnetic state below TN∼47.8K and a compensation temperature Tcomp∼32K, the latter characterized by sign reversal of magnetization with its magnitude depending on the applied magnetic field and the cooling protocol. Analysis of the temperature dependence of M (field cooled) and M (zero field cooled) data and the hysteresis loop parameters is interpreted in terms of large spin clusters. These results in Co2TiO4, significantly different from those reported recently in isostructural Co2SnO4=[Co2+][Co2+Sn4+]O4, warrant further investigations of its magnetic structure using neutron diffraction.