Structural Transformations and Magnetic Properties of Mixed Spinel-Type NiCr1.7Fe0.3O4 Nanoparticles

Abstract

Structural and magnetic properties of NiCr1.7Fe0.3O4 nanoparticles, synthesized by a facile coprecipitation method, are examined using temperature-dependent X-ray diffraction, neutron scattering with XYZ polarizations, and magnetic measurements. The structural analysis demonstrates the stabilization of the cubic phase down to 200 K, followed by a low-temperature tetragonal phase at 100 K and an orthorhombic phase below 50 K. The refined occupancies of cations demonstrate that the NiCr1.7Fe0.3O4 is a mixed spinel compound, wherein B sites are populated by ≈85% Cr3+ and ≈15% Ni2+ cations and A sites are populated by ≈70% Ni2+ and ≈30% Fe3+ cations. As a consequence, the reduction in the occupancy of Jahn–Teller active Ni2+ (triply degenerate: e4 t4) at A site is attributed to the stabilization of the cubic phase below room temperature. Temperature-dependent magnetization and neutron scattering with XYZ polarizations measurements reveal the ferrimagnetic nature of the magnetic phase and the absence of spin-spiral ordering in NiCr1.7Fe0.3O4 nanoparticles. Furthermore, field-dependent magnetization measurement demonstrates an exchange bias field of ≈134.5 kA m−1 at 5 K. The training effect measurement is performed to discuss the origin of exchange bias based on different phenomenological models such as power-law and multiexponent models. © 2021 Wiley-VCH GmbH