Stabilization of the high-spin state of Co3+^{3+} in LaCo1−x_{1-x}Rhx_{x}O3_3

The rhodium doping in the LaCo$_{1-x}$Rh$_{x}$O$_3$ perovskite series ($x=0.02-0.5$) has been studied by X-ray diffraction, electric transport and magnetization measurements, complemented by electronic structure GGA+U calculations in supercell for different concentration regimes. No charge transfer between Co$^{3+}$ and Rh$^{3+}$ is evidenced. The diamagnetic ground state of LaCoO$_3$, based on Co$^{3+}$ in low-spin (LS) state, is disturbed even by a small doping of Rh. The driving force is the elastic energy connected with incorporation of a large Rh$^{3+}$ cation into the matrix of small LS Co$^{3+}$ cations, which is relaxed by formation of large Co$^{3+}$ in high-spin (HS) state in the next-nearest sites to the inserted Rh atom. With increasing temperature, the population of Co$^{3+}$ in HS state increases through thermal excitation, and a saturated phase is obtained close to room temperature, consisting of a nearest-neighbor correlation of small (LS Co$^{3+}$) and large (HS Co$^{3+}$ and LS Rh$^{3+}$) cations in a kind of double perovskite structure. The stabilizing role of elastic and electronic energy contributions is demonstrated in supercell calculations for dilute Rh concentration compared to other dopants with various trivalent ionic radius.Comment: 8 pages, 8 figure

Metal-insulator transition and the Pr3+^{3+}/Pr4+^{4+} valence shift in (Pr1−y_{1-y}Yy_{y})0.7_{0.7}Ca0.3_{0.3}CoO3_3

The magnetic, electric and thermal properties of the ($Ln_{1-y}$Y$_{y}$)$_{0.7}$Ca$_{0.3}$CoO$_3$ perovskites ($Ln$~=~Pr, Nd) were investigated down to very low temperatures. The main attention was given to a peculiar metal-insulator transition, which is observed in the praseodymium based samples with $y=0.075$ and 0.15 at $T_{M-I}=64$ and 132~K, respectively. The study suggests that the transition, reported originally in Pr$_{0.5}$Ca$_{0.5}$CoO$_3$, is not due to a mere change of cobalt ions from the intermediate- to the low-spin states, but is associated also with a significant electron transfer between Pr$^{3+}$ and Co$^{3+}$/Co$^{4+}$ sites, so that the praseodymium ions occur below $T_{M-I}$ in a mixed Pr$^{3+}$/Pr$^{4+}$ valence. The presence of Pr$^{4+}$ ions in the insulating phase of the yttrium doped samples (Pr$_{1-y}$Y$_{y}$)$_{0.7}$Ca$_{0.3}$CoO$_3$ is evidenced by Schottky peak originating in Zeeman splitting of the ground state Kramers doublet. The peak is absent in pure Pr$_{0.7}$Ca$_{0.3}$CoO$_3$ in which metallic phase, based solely on non-Kramers Pr$^{3+}$ ions, is retained down to the lowest temperature.Comment: 10 figure

Investigation of magneto-structural phase transition in FeRh by reflectivity and transmittance measurements in visible and near-infrared spectral region

Magneto-structural phase transition in FeRh epitaxial layers was studied optically. It is shown that the transition between the low-temperature antiferromagnetic phase and the high-temperature ferromagnetic phase is accompanied by a rather large change of the optical response in the visible and near-infrared spectral ranges. This change is consistent with ab initio calculations of reflectivity and transmittance. Phase transition temperatures in a series of FeRh films with thicknesses ranging from 6 to 100 nm is measured thereby demonstrating the utility of the method to quickly characterise samples. Spatially resolved imaging of their magnetic properties with a micrometer resolution shows that the phase transition occurs at different temperatures in different parts of the sample

Magnetization Study of the AFM-FM Coexistence in the Manganite System Pr0.5Ca0.5−xSrxMnO3Pr_{0.5}Ca_{0.5-x}Sr_xMnO_3

For the manganites $Pr_{0.5}Ca_{0.5-x}Sr_xMnO_3$ (x=0;0.3) the temperature and cooling field dependence of the reduced remanence asymmetry indicates the antiferromagnetic exchange between the antiferromagnetic and ferromagnetic spins at the surface of the clusters. For x=0.3 we deduce the radius of the cluster in the field cooled regime to be about 20 times larger than that for x=0

Details of Magnetic Properties in Pb(Fe1/2Nb1/2)O3Pb(Fe_{1/2}Nb_{1/2})O_{3}

For $Pb(Fe_{0.5}Nb_{0.5})O_{3}$ the χ(T) and m(H) measurements up to 70 kOe were performed with the aim to estimate the antiferromagnetic (AFM) and superantiferromagnetic (SAF) contribution to χ(T). Below $T_{N}$ the increase of χ(T) is attributed to a small part of $Fe^{3+}$ ions in the SAF clusters. For high fields the suppression of the AFM and enhancement of the SAF susceptibility was observed. An inflection point of the m(H) curves below the Néel point suggests the presence of a spin reorientation process connected with the AFM phase

New Findings in Mössbauer Studies of Amorphous FeMoCuB NANOPERM-Type Alloy

The effect of heat treatments at 603 K (a relaxation of an amorphous structure) and at 723 K (an onset of a bulk nanocrystallization) of a rapidly quenched $Fe_{76}Mo_{8}Cu_{1}B_{15}$ alloy is studied. The differences in sample processing are reflected in magnetization direction as seen by room- and low-temperature Mössbauer spectroscopy

Cation disorder and size effects on the magnetic transition in Ba-containing ferromagnetic manganites

PACS. 75.30.Kz Magnetic phase boundaries (including magnetic transitions, metamagnetism, etc.) - 75.50.Dd Nonmetallic ferromagnetic materials - 76.60.-k Nuclear magnetic resonance and relaxation,

Structural and magnetic properties of Zn x Mn 3-x O 4 spinels

International audienceTo study structural and magnetic properties of spinels a series of ceramic samples with a different ZnMn ratio was prepared by high-temperature annealing in air followed by quenching in liquid nitrogen. The spinels with nominal composition of Zn x Mn 3-x O 4 (x=0-1.29) were characterized by means of X-ray diffraction, Raman spectroscopy, scanning electron microscopy and SQUID magnetometry. Two tetragonal spinels of the same I4 1 /amd space-group were identified based on the crystallographic, vibrational and grain-morphology point of view and described in detail. The unit-cell parameters and phase ratio of the spinel phases were determined using Rietveld refinement. According to the factor-group analysis the majority of the vibrational modes were identified in the Raman spectra. The magnetic properties of Zn x Mn 3-x O 4 spinels are in agreement with a model of nanoscale ferrimagnetic Mn 3 O 4 clusters in the antiferromagnetic ZnMn 2 O 4 matrix (T N ≈60 K). New features are a constricted hysteresis loop for x=0.3, and the effect of defects on magnetic properties for high Zn content which points to a good quality of the samples prepared by a solid state reaction. © 2016 Elsevier B.V. All rights reserved

Structural and magnetic properties of Zn x Mn 3-x O 4 spinels

To study structural and magnetic properties of spinels a series of ceramic samples with a different ZnMn ratio was prepared by high-temperature annealing in air followed by quenching in liquid nitrogen. The spinels with nominal composition of Zn x Mn 3-x O 4 (x=0-1.29) were characterized by means of X-ray diffraction, Raman spectroscopy, scanning electron microscopy and SQUID magnetometry. Two tetragonal spinels of the same I4 1 /amd space-group were identified based on the crystallographic, vibrational and grain-morphology point of view and described in detail. The unit-cell parameters and phase ratio of the spinel phases were determined using Rietveld refinement. According to the factor-group analysis the majority of the vibrational modes were identified in the Raman spectra. The magnetic properties of Zn x Mn 3-x O 4 spinels are in agreement with a model of nanoscale ferrimagnetic Mn 3 O 4 clusters in the antiferromagnetic ZnMn 2 O 4 matrix (T N ≈60 K). New features are a constricted hysteresis loop for x=0.3, and the effect of defects on magnetic properties for high Zn content which points to a good quality of the samples prepared by a solid state reaction. © 2016 Elsevier B.V. All rights reserved