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Several papers reported the experimental phenomena of single crystal orthoferrite DyFeO3 samples: the sample magnetization increases with increasing temperature, under a constant low magnetic field along the easy magnetizing direction of the samples, and then reaches a maximum value. These phenomena are better explained using magnetic domain wall pinning at low temperatures and depinning at high temperatures, which were neglected in previous papers. In this article, we argue that the magnetic domain wall motion must be taken into consideration in order to explain these experimental phenomena. Based on an O 2p itinerant electron model, we discussed the role of the magnetic domain and the characteristics of cation magnetic moments in relevant single crystal materials. [ABSTRACT FROM AUTHOR]

Powder samples of the ferrites MxNi1-xFe2O4 (M = Cr, Co and 0.0 ≤ x ≤ 0.3) were prepared using a chemical co-precipitation method. X-ray diffraction analysis showed that the two series of samples had a single-phase cubic spinel structure. It was found that the magnetic moments (μexp) per formula of samples measured at 10 K decreased when Cr substituted for Ni, but increased when Co substituted for Ni, in spite of the fact that the magnetic moments of Cr2+ (4 μB) and Co2+ (3 μB) are higher than that of Ni2+ (2 μB). With the assumption that the magnetic moments of Cr2+ and Cr3+ lie antiparallel to those of the Fe, Co, and Ni cations in the same sublattices of spinel ferrites, the dependences on the Cr (Co) doping level of the sample magnetic moments at 10 K were fitted successfully, using the quantum-mechanical potential barrier model earlier proposed by our group. For the two series of samples, the fitted magnetic moments are close to the experimental results. [ABSTRACT FROM AUTHOR]

The effects of lanthanum deficiency on the structural and magnetic properties of manganites with normal composition La0.7-xSr0.3MnO3 prepared by the sol-gel method with the highest heat treatment temperature at 800 °C have been investigated. X-ray diffraction (XRD) spectra indicate that the materials possess a single phase with the R3c perovskite structure for x≤0.05, and that they possess two phases with the R3c perovskite being the dominant phase and Mn3O4 being the second phase for x≥0.10. Using XRD analysis, these materials can be expressed as La0.7-xSr0.3Mn1-yO3-1.5(x+y)/(Mn3O4)y/3. On the basis of the thermal equilibrium theory of crystal defects, the ion ratios at the A, B, and O sites in the ABO3 perovskite phase were calculated. Those ion ratios were used in Rietveld fitting of the XRD spectra. It was found that the dependence of the Curie temperature TC on the content ratio RM4 of Mn4+ ions at B site is similar to that of the typical perovskite La1-xSrxMnO3. [ABSTRACT FROM AUTHOR]

Powder samples of the ABO3 perovskite manganites Pr0.6Sr0.4CrxMn1-xO3 (0.00≤x≤0.30) were synthesized using the sol-gel method. X-ray diffraction analyses showed that all the samples had a single-phase orthorhombic structure. By analyzing magnetic parameters on the basis of the O2p itinerant electron model, we found that there are two magnetic transition temperatures, TCM and TCP, corresponding to changes in the magnetic ordering for the Mn and Pr cations, respectively. The magnetic moments of Mn3+ and Cr3+ cations within the B sublattice show canted ferromagnetic coupling, and the magnetic moments of the Pr cations within the A sublattice also show canted ferromagnetic coupling. However, the total magnetic moment of the A sublattice shows antiferromagnetic coupling against that of the B sublattice. The assumption of the canted ferromagnetic coupling within the B sublattice was confirmed using magnetoresistance experimental results. [ABSTRACT FROM AUTHOR]

Powder samples of the ferrites MxMn1-xFe2O4 (M = Zn, Mg, Al) were prepared using a chemical co-precipitation method. X-ray diffraction analysis showed that the three series of samples had a single-phase cubic spinel structure and that there was a decrease in the lattice parameters with increasing x. There were different dependences on the doping level x of the magnetic moments (µexp) for the three series of samples measured at 10 K. We found a non-monotonic behavior for µexp as a function x for the Zn doped samples with a maximum at x = 0.4, while µexp decreased monotonically with increasing x for the Mg and Al doped samples. On the basis of the O2p itinerant electron model, the magnetic moment direction of the Mn3+ cations is expected to be antiparallel to those of the Mn2+ and Fe cations in these samples. With this assumption, the curves of µexp versus x for the three series of samples were fitted using a quantum-mechanical potential barrier model earlier proposed by our group, and the cation distributions were obtained. [ABSTRACT FROM AUTHOR]

Ferrite powder samples of Mn xNi1- xFe2O4 (0.0 ≤ x ≤ 1.0) with single phase (A)[B]2O4 spinel structure were prepared using a sol-gel method. Following the successful proposal by our group, that the magnetic moment directions of Cr2+ (3d4) cations are antiparallel to those of Fe3+ (3d5) and Fe2+ (3d6) cations in a given sublattice of the Cr-doped spinel ferrites due to the constraints imposed by Hund's rules, we extend here the same idea and assume that the magnetic moment directions of Mn3+ (3d4) cations are also antiparallel to those of Mn2+ (3d5) and divalent and trivalent Fe (Ni) cations in a given sublattice of Mn-doped spinel ferrites. We have thereby obtained cation distributions for the samples by fitting the magnetic moments of the samples at 10 K. The results indicate that 72% of the Mn cations occupy the [B] sites in MnFe2O4, which is close to the results for Ni (82%) in NiFe2O4, but is different from the result obtained using the conventional view which yields 80% of the Mn cations in the (A) sites of MnFe2O4. On the basis of the present analyses of the magnetic structure of Mn xNi1- xFe2O4 (0.0 ≤ x ≤ 1.0), we propose here a new model for spinel ferrites that is distinctly different from both the super- and the double-exchange model and that we refer to as the O2p itinerant electron model. Using this model, not only can the magnetic structure of the spinel ferrites MFe2O4 ( M = Fe, Co, Ni, and Cu) be explained better than by using the super- and double-exchange interaction models, but also the magnetic structure and the cation distributions of Cr-, Mn-, and Ti-doped spinel ferrites can be explained. [ABSTRACT FROM AUTHOR]

Powder samples of the spinel ferrites MxNi0.7-xFe2.3O4 (M = Cr, Co and 0.0 ≤ x ≤ 0.3) and CrxNi0.7Fe2.3-xO4 (0.0 ≤ x ≤ 0.3) were synthesized using the chemical co-precipitation method. The XRD spectra confirmed that the samples had a singlephase cubic spinel structure. Magnetic measurements showed that the magnetic moments (μexp) per formula both at 10 K and 300 K increased with Co substitution, while the values of μexp decreased with Cr substitution. Applying the assumption that the magnetic moments of Cr2+ and Cr3+ lie antiparallel to those of the divalent and trivalent Fe, Co, and Ni cations in the same sublattice of spinel ferrites, these interesting behaviors could be easily interpreted. The cation distributions of the three series of samples were estimated successfully by fitting the dependences of μexp, measured at 10 K, on the doping level x, using a quantum-mechanical potential barrier model earlier proposed by our group. The results obtained for the Cr cation distributions at the (A) and [B] sites are very close to those obtained elsewhere using neutron diffraction. [ABSTRACT FROM AUTHOR]

Ti-doped Ni0.68Fe2.32O4 spinel ferrite samples with nominal composition Ni0.68−0.8 xTi xFe2.32−0.2 xO4 (0 ≤ x ≤ 0.312) were prepared using conventional ceramic methods. The samples exhibited a single-phase cubic spinel structure. When the doping level had values x > 0.15, a transition temperature, TN, was found, below which the magnetization of the samples decreased with decreasing measurement temperature. This phenomenon indicates that an additional antiferromagnetic structure arises in the traditional spinel phase of ferrites resulted from Ti doping. Therefore, Ti ions appear in the form of Ti3+ and Ti2+ cations that have magnetic moments, rather than as Ti4+ cations without magnetic moment as assumed by many researchers. The dependence of the magnetic moments on the Ti doping level x at 10 K was fitted successfully using our quantum-mechanical potential barrier model proposed earlier. In the fitting process, we assumed that the magnetic moments of the Ti cations were opposite to the direction of the Fe and Ni moments. According to the fitted results, the Ti2+ cations at the [B] sites constitute about 81% of the total Ti content x for all samples, which is close to the content of the Ni2+ cations at the [B] sites (77%). [ABSTRACT FROM AUTHOR]