Superparamagnetic clusters at room temperature, anomalous magnetic coercivity and spin-flop transition in novel dilute antiferromagnetic nanoparticles of La2Fe0.875Cr0.125GaO6

Abstract Magnetism at the nanoscale is intriguing, but that on the magnetic properties of a dilute antiferromagnetic (AFM) system is rarely studied. Presence of uncompensated spins at the lattice as well as on the nanoparticle surfaces could lead to interesting magnetic behaviour. We present the combined effect of reduction in particle size and dilution of exchange interactions on the magnetic properties of an AFM perovskite oxide. A dilute AFM compound, La 2 Fe 0.875 Cr 0.125 GaO 6 nanoparticles (average particle size ∼ 44.5 (7) nm), has been synthesized where non-magnetic Ga-ions are introduced to interrupt the superexchange pathways. The compound crystallizes in orthorhombic structure with Pbnm space group, where Fe, Cr and Ga ions are distributed randomly in the B-site. DC magnetic studies show superparamagnetic behaviour at room temperature, spin-flop transition and a prominent hysteresis loop with sufficiently high coercivity around 6.69 kOe at ∼138 K. The analysis of thermoremanent and isothermoremanent magnetization curves reveal SPM behaviour at 300 K and 2-dimensional dilute antiferromagnetic in field like nature at 5 K. AC magnetic susceptibility analysis confirms the presence of non-interacting clusters having SPM behaviour with blocking temperature ∼280 K. Furthermore, temperature variation of coercivity shows a Gaussian nature, mainly associated with competing Dzyaloshinskii-Moriya interactions between disordered B-site ions along with strong uncompensated surface spin effects.