Structure, optical and varying magnetic properties of insulating MCr2O4 (M= Co, Zn, Mg and Cd) nanospinels

Chromite nanospinels of MCr2O4 (M = Co, Zn, Mg and Cd) have been synthesized using a microwave combustion method. The spinel phase and average particles size have been investigated by powder X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and transmission electron microscopy...

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Bibliographic Details
Published in:Journal of alloys and compounds 2019-06, Vol.790, p.853-862
Main Authors: Kassem, Mohamed A., Abu El-Fadl, Abdulaziz, Nashaat, Ahmed M., Nakamura, Hiroyuki
Format: Article
Language:English
Subjects:
Antiferromagnetism
Cadmium
Chromite
Chromite nanospinels
Cobalt
Curie temperature
Dependence
Divalent cations
Energy gap
Ferrimagnetism
Fourier transforms
Magnesium
Magnetic properties
Magnetic transitions
Magnetism
Magnetization
Nanocrystals
Nanoparticles
Optical properties
Particle size
Superparamagnetism
Temperature
Transmission electron microscopy
Wide energy gap
X ray powder diffraction
X-ray diffraction
XRD
Zinc
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Summary:Chromite nanospinels of MCr2O4 (M = Co, Zn, Mg and Cd) have been synthesized using a microwave combustion method. The spinel phase and average particles size have been investigated by powder X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and transmission electron microscopy (TEM). Both XRD and TEM reveal an overall average particle size of about 12 nm. UV–Vis optical absorbance measurements at room temperature indicate common wide optical energy gap of about 3.1–3.4 eV. Magnetization processes have been studied via precise field cooled (FC) and zero-field cooled (ZFC) magnetization measurements. The magnetic transition temperatures found in the nanoparticles are slightly below those of corresponding bulk crystals. Survived spiral spin textures below ∼26 K and coexisting spin-glassy state are observed in the Néel-type ferrimagnetic CoCr2O4 nanocrystals with Curie temperature of 92 K. While the antiferromagnetic state of chromites with nonmagnetic divalent cations is observed in ZnCr2O4 nanocrystals below Néel temperature of 11 K, it is significantly suppressed in MgCr2O4 and CdCr2O4 nanocrystals of identical average particle size. Our results indicate increased surface spins contribution with increasing lattice parameter. ESR linewidth and resonance field of MCr2O4 also show M-cation type dependence. The coexisting spin-glassy-like state in long-range ordered CoCr2O4 and a possible superparamagnetic state in MCr2O4 (M = Zn, Mg and Cd) nanospinels are discussed as finite-size and Cr-Cr separation effects. [Display omitted] •XRD, FTIR and TEM indicate single nanospinel phase of ∼12 nm in particle size.•Overall wide energy gap of ∼3.2 eV is demonstrated by UV–Vis optical measurements.•FIM CoCr2O4 nanocrystals exhibit coexisting spin glassy and survived spiral spin states.•Varying suppression limit of the AF state in MCr2O4 (M = Zn, Mg, Cd) nanospinels is observed.•AF suppression is attributed to spin surface contribution depends on lattice parameter.
ISSN:0925-8388
1873-4669
DOI:10.1016/j.jallcom.2019.03.189