Abstract
Nanoparticles of (Co1–xNix)Cr2O4, with x = 0.5 and 0.25, were prepared utilizing the sol-gel technique, in order to investigate the effect of Ni substitution at the Co site. The crystal structure of the prepared samples was identified using X-ray diffraction. Transmission electron microscopy images indicate a non-uniform distribution in particle sizes. Temperature dependent magnetization measurements as a function of probing field demonstrate different magnetic transition temperatures to that of both the parent compounds. The magnetization as a function of applied magnetic field shows a wasp-waist like feature for (Co0.5Ni0.5)Cr2O4 nanoparticles measured at 10 K, which is absent in both NiCr2O4 and CoCr2O4. This feature diminished for other measurement temperatures below the Curie temperature and was also absent at all temperatures for the (Co0.75Ni0.25)Cr2O4 nanoparticles. X-ray photoemission spectroscopy results show that the Ni cations prefers the 3+ and Co the 2+ oxidation states, while that of Cr was found to be 3+. However, mixed oxidation states were observed for Ni and Co in both samples, which can influence the magnetic properties.
Highlights
CoCr2O4 is a well-studied ferrimagnetic material,[1] with a collinear ferrimagnetic phase below T C ≈ 93 K.1 CoCr2O4 obtains a remanent magnetic moment from the Co and Cr sublattices aligning antiparallel along [001].1 In addition a spiral ordering at T S ≈ 26 K and a lock-in transition at T L ≈ 15 K, as well as strong magneto-electric coupling have been reported for this compound.[2]
Structural and morphological characterizations were carried out using X-ray diffraction (XRD) with Cu–Kα radiation and a 200 kV analytical transmission electron microscope (TEM), respectively
Ferrimagnetic behaviour was observed in the M(μ0H) curves for T < T C, with non-saturated magnetization up to fields of 12 T, in both samples
Summary
CoCr2O4 is a well-studied ferrimagnetic material,[1] with a collinear ferrimagnetic phase below T C ≈ 93 K.1 CoCr2O4 obtains a remanent magnetic moment from the Co and Cr sublattices aligning antiparallel along [001].1 In addition a spiral ordering at T S ≈ 26 K and a lock-in transition at T L ≈ 15 K, as well as strong magneto-electric coupling have been reported for this compound.[2]. The magnetic properties can be altered by substituting cations with different ions of suitable size and oxidation state. Considering that size reduction to nanoscale alters the magnetic properties,[10] together with the ferroelectricity[11] and enhancement[12] of T C previously observed in bulk Co1 xNixCr2O4, similar work on analogous doped chromite nanoparticles should be interesting. This study extends investigations into nanoparticle form, in order to explore the modification in structural and magnetic properties
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