Room temperature ferrimagnetism, magnetodielectric and exchange bias effect in CoFeRhO4 (original) (raw)
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Temperature-dependent multi-k magnetic structure in multiferroic Co3TeO6
Materials Research Bulletin, 2012
A complex magnetic order of the multiferroic compound Co 3 TeO 6 has been revealed by neutron powder diffraction studies on ceramics and crushed single crystals. The compound adopts a monoclinic structure (s.g. C2/c) in the studied temperature range 2 K -300 K but exhibits successive antiferromagnetic transitions at low temperature. Incommensurate antiferromagnetic order with the propagation vector k 1 = (0, 0.485, 0.055) sets in at 26 K. A transition to a second antiferromagnetic structure with k 2 = (0, 0, 0) takes place at 21.1 K. Moreover, a transition to a commensurate antiferromagnetic structure with k 3 = (0, 0.5, 0.25) occurs at 17.4 K. The magnetic structures have been determined by neutron powder diffraction using group theory analysis as a preliminary tool. Different coordinations of the Co 2+ ions involved in the low-symmetry C2/c structure of Co 3 TeO 6 render the exchange-interaction network very complex by itself. The observed magnetic phase transformations are interpreted as an evidence of competing magnetic interactions. The temperature dependent changes in the magnetic structure, derived from refinements of highresolution neutron data, are discussed and possible mechanisms connected with the spin reorientations are described.
Spatial inhomogeneity of magnetic moments in the cobalt oxide spinelCo3O4
Physical Review B, 2007
The antiferromagnetic ͑AF͒ nature of the normal spinel Co 3 O 4 with Néel temperature ͑T N ͒ =30 K was investigated by means of positive muon spin rotation and relaxation ͑ + SR͒ techniques using a polycrystalline sample. Clear muon spin precession signals due to a quasistatic long-range AF order were found in the zero-field + SR spectra below T N. The spectra consist of two oscillating signals with frequencies at T → 0 K of 80 and 60 MHz, respectively, indicating an incommensurate ͑IC͒ AF order in Co 3 O 4. A possible reason for the appearance of the IC-AF order in Co 3 O 4 would be local structural transitions due to a charge and/or a spin state change of Co ions.
Effect of boron content on structure and magnetic properties in CoFe2O4 spinel nanocrystals
Journal of Alloys and Compounds, 2018
We study the effect of boron content on the structural and magnetic properties of CoFe 2 O 4 spinel nanocrystallines synthesized by sol-gel method. The crystal structure and phase identification of samples are studied by using X-ray diffraction experiment and Rietveld analysis. Rietveld refinement results reveal that all samples have cubic symmetry with space group Fd3m. The cationic distributions are obtained from Rietveld refinement that boron ions are settled into both tetrahedral and octahedral sites in spinel lattice. The crystallite sizes of samples are found in a range of 47e67 nm that is in the limit of single domain in such structure. All samples show ferromagnetic nature and magnetic transition was not seen in the temperature range of 5e400 K. The magnetic domains are pinned with adding boron ions into the CoFe 2 O 4 spinel structure at low temperatures. Thus, an increment in the propagation field (H p) and temperature (T p) by boron content in CoFe 2 O 4 structure is observed. In addition, the saturation magnetization (M s) normalized by crystal size increases with increasing boron concentration. The temperature dependence of magnetic properties of the samples taken by experimental data are confirmed with the Neel-Arhenius model by adding thermal dependence of magnetocrystalline anisotropy term. The results indicate that boron-doping into the spinel structure enhances ferromagnetic coupling and suppresses super-exchange interaction between tetrahedral (X) and octahedral (Y) sites.
Journal of Applied Physics, 2015
In this paper, we establish the negative spontaneous magnetization in Mn and Zn substituted cobalt ferrite Co 0.6 Zn 0.4 Fe 1.7 Mn 0.3 O 4 (CZFMO). It is suggested that the origin of negative spontaneous magnetization is due to the substitution of small sized Mn þ4 ions (compared to Fe þ3 ions) at the octahedral B site in compound Co 0.6 Zn 0.4 Fe 2 O 4. The low value of Poisson's ratio $0.202 for this compound possibly contributes towards the easy distortion in the bond length and bond angle, causing increase in Fe-O bond distance/decrease in Fe-O-Fe bond angle with Mn substitution, leading to considerably weak Fe-O-Fe superexchange interaction at the octahedral B site. The neutron diffraction data clearly illustrated the significant reduction in ordered magnetic moment at the B site, with the resultant negative spontaneous magnetization (M ¼ M B À M A) in this mixed spinel system. The spin disorder also gives rise to an interesting semi-spin glass behavior in CZFMO.
Ceramics International, 2014
The effect of Mn substitution on temperature dependent magnetic properties of Mn substituted cobalt ferrite, i.e., Co 1−x Mn x Fe 2 O 4 (x ¼0.0-0.4), prepared by a ceramic method has been investigated. X-ray diffraction (XRD) analysis reveals that all samples posses a single phase cubic spinel structure. The lattice constant determined from XRD increases with Mn substitution whereas the bulk density of the samples decreases. Mössbauer results reveal that Co, Fe and Mn ions are distributed over the tetrahedral (A) and octahedral (B) sites for the prepared samples. Hysteresis loops yield a saturation magnetization (M s ) and coercive field (H c ) that vary significantly with temperature and Mn content (x). The temperature dependence of the magnetization obtained for μ o H¼ 5 T presents a maximum at 175 K which is also dependent on the value of x. The high field regimes of the hysteresis loops are modeled using the Law of Approach to Saturation (LAS) to determine the first-order cubic anisotropy coefficient (K 1 ). It has been found that the anisotropy of these materials increases significantly with decreasing temperature. However, below 175 K, the shape of the anisotropy energy function changes significantly causing a first-order magnetization process (FOMP) at higher fields, which also prevents the magnetization to saturate even under a maximum applied field of 5 T. In general, the anisotropy coefficient decreases with increasing Mn substitution at a given temperature, which could be explained in terms of the site occupancy of the Mn 2+ substituent in the cubic spinel lattice.
Physical Review B
A detailed account of magnetolattice coupling, magnetic frustration, and magnetoelectric effects in Fe 1−x Cr x VO 4 (x = 0 − 1.0) studied by temperature-dependent synchrotron x ray diffraction (SXRD), temperature-and magnetic-field-dependent dielectric permittivity ε, and magnetization measurements are presented in this paper where progressive Cr doping leads to structural transitions from triclinic (T)-monoclinic (M)-orthorhombic (O) symmetries. SXRD data shows an intricate relationship between magnetic, ferroelectric, and lattice degrees of freedom in these systems. FeVO 4 reaches a magnetically ordered state with two successive antiferromagnetic orderings at T N1 (21.85 K) and T N2 (15.65 K), having collinear and noncollinear natures, respectively, as evidenced in DC magnetization measurements. Progressive Cr 3+ incorporation at the Fe 3+ site in Fe 1−x Cr x VO 4 shifts these transitions to higher temperatures in T phase (x = 0.0 and 0.10). At x = 0.175 [in (T + M) phase], these transitions become closer to each other. Beyond this concentration, a single broad antriferromagnetic transition is observed in M (x = 0.20 − 0.30) and O (x = 0.90 − 1.0) phases. A nonlinear behavior in isotherm M-H curves below T N2 indicates field-induced spin-reorientation transitions at higher magnetic field. In dielectric permittivity ε a sharp peak at T N2 in T and near M regions with a minimal suppression because of applied magnetic field is found and no such peak is observed in far M phase. A discontinuity evidenced in electromagnetic susceptibility indicates magnetoelectric effect at the polar to nonpolar transition regions. The structural incongruence in progressive transformation from T to M to O symmetries plays a vital role in controlling the nature of magnetic interactions. Our results indicate a strong correlation between structural transitions, magnetolattice coupling, magnetic frustrations, and magnetoelectric effect in Fe 1−x Cr x VO 4 .
Spin effect on electronic, magnetic and optical properties of spinel CoFe2O4: A DFT study
Materials Science and Engineering B , 2020
This report demonstrates the structural, electronic, magnetic, elastic, and optical properties of spinel CoFe2O4 using generalized gradient approximation (GGA). Both the spin and non-spin polarized density functional theory (DFT) have been used to study the influence of spin interactions on electronic structures, spin magnetic mo- ments, and optical properties. The calculated magnetic moments of CoFe2O4 from spin density of states are 6.98 μB per formula unit. The Fe and Co ions prefer high spin orientations owing to the cationic polarization because of crystal field strength and intra-atomic exchange interactions, which induces large spin magnetic moments. The high values of spin magnetic moments confirm strong spin orbit coupling due to strong electron-electron interactions and can be a promising for spintronic application. Moreover, the calculated high reflectivity of CoFe2O4 material (~100%) in the Infrared-Visible-Ultraviolet region up to ~30 eV, which suggesting that the CoFe2O4 can also be a good candidate for solar reflector.