Investigation on magnetic contribution of constituent elements in Co1-xNixCr2O4 spinel chromites

CoCr2O4 (CCO) undergoes complex magnetic phase transitions at low temperatures. In its cubic phase with Fd-3m symmetry, Co ions occupy tetrahedral sites with a 2+ charge state, while Cr ions reside in octahedral sites with a 3+ charge state, creating a cubic close-packed lattice within an O2- environment. Around 95 K(TC), a significant transition from paramagnetic to ferrimagnetic state occurs. Below 25 K (TS), structural frustration induces spiral magnetic ordering, leading to an incommensurate non-collinear system with spin-induced polarization, exhibiting multiferroicity below TS. At TL~13 K, a lock-in transition stabilizes the spins. However, a comprehensive understanding of these transitions is still lacking. Our initial studies on Ni doped and undoped CCO reveal some anomalous behaviour in magnetization data at 180 K, higher than TC. Photoelectron spectroscopy reveal hetero-valency in Co, Cr, and Ni, which would influence the magnetic properties. Investigations on the charge states of these atoms and their magnetic contributions with temperature variation is crucial for understanding their interactions. Temperature-dependent X-ray Magnetic Circular Dichroism (XMCD) experiments, ranging from 5 K to 300 K, offer valuable insights. XMCD enables exploration of the spin and orbital magnetic moment contributions of constituent cations at various temperatures, impacting their exchange interactions. Comparative analysis of XMCD spectra between Ni-doped and undoped CCO samples will reveal changes in magnetic moments, unveiling the nature of spin alignment and strengths of interactions between constituent cations. This investigation will help in illuminating the competitive magnetic alignments within the material, advancing our understanding of CCO (doped and undoped) magnetic behaviour.
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