Comparison of anomalous magnetic properties of non-collinear CoCr2O4 and NiCr2O4 nanoparticles

•Tc was high for CoCr2O4 nanoparticles as compared to NiCr2O4.•A high value of Hc was observed for NiCr2O4 nanoparticles.•Larger canted angle increases the Hc value of NiCr2O4 nanoparticles.•NiCr2O4 nanoparticles follow the Bloch’s law with high value of Bloch’s constant and exponent.•CoCr2O4 nanopa...

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Bibliographic Details
Published in:Journal of magnetism and magnetic materials 2020-11, Vol.514, p.167225, Article 167225
Main Authors: Rasool, R. Zohaib, Nadeem, K., Kamran, M., Zeb, F., Ahmad, Naman, Mumtaz, M.
Format: Article
Language:English
Subjects:
Chromite
CoCr2O4
Coercivity
Ferrimagnetism
Low temperature
Magnetic measurement
Magnetic properties
Multiferroic
Nanoparticles
NiCr2O4
Size effects
Temperature dependence
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Summary:•Tc was high for CoCr2O4 nanoparticles as compared to NiCr2O4.•A high value of Hc was observed for NiCr2O4 nanoparticles.•Larger canted angle increases the Hc value of NiCr2O4 nanoparticles.•NiCr2O4 nanoparticles follow the Bloch’s law with high value of Bloch’s constant and exponent.•CoCr2O4 nanoparticles do not follow Bloch’s law predicted trend. Temperature-dependent magnetic properties of cobalt chromite (CoCr2O4) and nickel chromite (NiCr2O4) nanoparticles (NPs) have been compared by using magnetic measurements. The average particle size of CoCr2O4 and NiCr2O4 NPs deduced from TEM images was found to be 48 and 46 nm, respectively. The NiCr2O4 NPs showed paramagnetic to ferrimagnetic transition (Tc) at 84 K which is relatively lower than the Tc = 98 K for CoCr2O4 NPs. The temperature dependent Ms value for CoCr2O4 NPs showed deviation from Bloch’s law at low temperatures which may be due to the existence of lock-in and strong conical spin spiral state. NiCr2O4 NPs showed a good Bloch’s law fit with high value of Bloch’s constant B = 0.00183 K−1 and low value of Bloch’s exponent b = 1.23 than their respective bulk value which indicates the presence of disordered surface spins and finite size effect in these NPs. Interestingly, a high value of Hc (5 K) was observed for NiCr2O4 NPs relative to CoCr2O4 NPs which is attributed to the large canted angle between the oxygen and metallic cations in NiCr2O4 NPs. Temperature dependent coercivity (Hc) for both the NPs were fitted with Kneller’s law. The Kneller’s law fit to Hc vs. T data revealed an exponent α = 0.46 for CoCr2O4 NPs which indicates the non-interacting particles with uni-axial symmetry, while it was 0.74 for NiCr2O4 NPs indicating the assembly of randomly oriented particles. In summary, CoCr2O4 and NiCr2O4 NPs showed a different low temperature magnetic response which is also relatively different than counter ferrite NPs.
ISSN:0304-8853
1873-4766
DOI:10.1016/j.jmmm.2020.167225