Crystal and magnetic structures of Cr1/3NbSe2 from neutron diffraction

Under a Creative Commons Attribution (CC BY) license.-- et al.Neutron diffraction measurements of the Cr intercalated niobium diselenide CrNbSe together with magnetization measurements have revealed that this compound exhibits ferromagnetic ordering below T = 96 K unlike a chiral helimagnetic order observed in the sulfide compound CrNbS. As derived from neutron diffraction data, the Cr magnetic moments μ = 2.83 ± 0.03 μ in CrNbSe are aligned within basal plane. The discrepancy in the magnetic states of CrNbS and CrNbSe is ascribed to the difference in the preferential site occupation of Cr ions in crystal lattices. In CrNbSe, the Cr ions are predominantly distributed over 2b Wyckoff site, which determines a centrosymmetric character of the crystal structure unlike CrNbS, where the Cr ions are mainly located in 2c position and the crystal structure is non-centrosymmetric.This work is partly based on experiments performed at the Japan Proton Accelerator Research Complex J-PARC. This work was performed within the state assignment of the FASO of Russia (No. 01201463334) and supported by Act 211 Government of the Russian Federation (Contract No. 02.A03.21.0006), by the Russian Foundation for Basic Research (Project Nos. 13-02-00364 and 13-02-92104), by the program of UB of RAS (Project No. 15-17-2-22), and by Grants-in-Aid for Scientific Research (Nos. 25220803, 242440590, and 25246006) from the Ministry of Education, Culture, Sports, Science and Technology (MEXT), Japan. This work was also supported by the Center for Chiral Science in Hiroshima University (the MEXT program for promoting the enhancement of research universities, Japan) and JSPS Core-to-Core Program, A. Advanced Research Networks. J.C. and Y.K. acknowledge the Grant No. MAT2011-27233-C02-02.Peer Reviewe

Magnetization in AIIIBV semiconductor heterostructures with the depletion layer of manganese

The magnetic moment and magnetization in GaAs/Ga$_{0.84}$In$_{0.16}$As/GaAs heterostructures with Mn deluted in GaAs cover layers and with atomically controlled Mn $\delta$-layer thicknesses near GaInAs-quantum well ($\sim$3 nm) in temperature range T=(1.8-300)K in magnetic field up to 50 kOe have been investigated. The mass magnetization all of the samples of GaAs/Ga$_{0.84}$In$_{0.16}$As/GaAs with Mn increases with the increasing of the magnetic field that pointed out on the presence of low-dimensional ferromagnetism in the manganese depletion layer of GaAs based structures. It has been estimated the manganese content threshold at which the ferromagnetic ordering was found.Comment: 8 pages, 3 figure

Pseudobinary Fe4Ti3S8 compound with a NiAs-type structure: Effect of Ti for Fe substitution

The transition metal sulfide Fe4Ti3S8 with 7:8 composition has been synthesized and studied by using X-ray diffraction, magnetization and electrical resistivity measurements. This compound exhibits a monoclinic crystal lattice (space group I12/m1). The substitution of Ti for Fe in Fe7S8 is found to result in a lowering of the Curie temperature (TC ≈ 205 K), in a larger value of the coercive field (Hc ∼ 9 kOe at low temperatures) and in a substantial growth of the resultant magnetic moment per formula unit (μFU) in comparison with Fe7S8. An enhanced value of μFU is attributed to the preferential substitution of Ti in alternating cation layers. From the paramagnetic susceptibility measured within temperature interval (250-350) K, a reduced value of the effective moment per iron (μFe ∼ 2.4μB) was determined. The electrical resistivity of Fe4Ti3S8 shows a non-metallic behavior and is affected by magnetic ordering. © 2013 Elsevier Masson SAS. All rights reserved

Voltage and temperature dependence of the grain boundary tunneling magnetoresistance in manganites

We have performed a systematic analysis of the voltage and temperature dependence of the tunneling magnetoresistance (TMR) of grain boundaries (GB) in the manganites. We find a strong decrease of the TMR with increasing voltage and temperature. The decrease of the TMR with increasing voltage scales with an increase of the inelastic tunneling current due to multi-step inelastic tunneling via localized defect states in the tunneling barrier. This behavior can be described within a three-current model for magnetic tunnel junctions that extends the two-current Julliere model by adding an inelastic, spin-independent tunneling contribution. Our analysis gives strong evidence that the observed drastic decrease of the GB-TMR in manganites is caused by an imperfect tunneling barrier.Comment: to be published in Europhys. Lett., 8 pages, 4 figures (included

Magnetic order in double-layer manganites (La(1-z)Pr(z))1.2Sr1.8Mn2O7: intrinsic properties and role of the intergrowths

We report on an investigation of the double-layer manganite series (La(1-z)Pr(z))1.2Sr1.8Mn2O7 (0 <= z <= 1), carried out on single crystals by means of both macroscopic magnetometry and local probes of magnetism (muSR, 55Mn NMR). Muons and NMR demonstrate an antiferromagnetically ordered ground state at non-ferromagnetic compositions (z >= 0.6), while more moderate Pr substitutions (0.2 <= z <= 0.4) induce a spin reorientation transition within the ferromagnetic phase. A large magnetic susceptibility is detected at {Tc,TN} < T < 250K at all compositions. From 55Mn NMR spectroscopy, such a response is unambiguously assigned to the intergrowth of a ferromagnetic pseudocubic phase (La(1-z)Pr(z))(1-x)Sr(x)MnO3, with an overall volume fraction estimated as 0.5-0.7% from magnetometry. Evidence is provided for the coupling of the magnetic moments of these inclusions with the magnetic moments of the surrounding (La(1-z)Pr(z))1.2Sr1.8Mn2O7 phase, as in the case of finely dispersed impurities. We argue that the ubiquitous intergrowth phase may play a role in the marked first-order character of the magnetic transition and the metamagnetic properties above Tc reported for double-layer manganites.Comment: 11 pages, 9 figures. Submitted to Phys. Rev.

Unconventional magnetism of non-uniform distribution of Co in TiO2 nanoparticles

High-resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD) analysis, electron paramagnetic resonance (EPR), X-ray absorption spectroscopy (XAS), magnetic methods, and density-functional theory (DFT) calculations were applied for the investigations of Co-doped anatase TiO2 nanoparticles (∼20 nm). It was found that high-spin Co2+ ions prefer to occupy the interstitial positions in the TiO2 lattice which are the most energetically favourable in compare to the substitutional those. A quantum mechanical model which operates mainly on two types of Co2+ – Co2+ dimers with different negative exchange interactions and the non-interacting paramagnetic Co2+ ions provides a satisfactorily description of magnetic properties for the TiO2:Co system. © 2020 Elsevier B.V.Russian Foundation for Basic Research. Ministry of Science and Higher Education of the Russian Federatio

Critical behavior study of magnetic transitions in Dy3Co single crystals

An ac photopyroelectric calorimeter has been used to study the critical behaviour of the magnetic transitions in Dy3Co measuring thermal diffusivity, specific heat and thermal conductivity, at low temperature. There are two phase transitions, both of which present singularities in the three variables. The antiferromagnetic to paramagnetic phase transition at 42 K complies with the short range, isotropic universality class, 3D-Heisenberg (alfaexp = -0.133 for specific heat, bexp = -0.145 for thermal diffusivity, alfatheor = btheor = -0.13). In the case of the lower transition where there is a rearrangement of the antiferromagnetic spin ordering at 32 K the critical behavior shows a deviation from isotropy. These results are linked to magnetic measurements already found in literature.This work has been supported by Universidad del País Vasco/Euskal Herriko Unibertsitatea (UPV/EHU-GIU16/93) and also partially supported by FASO of Russia (themes No 01201463328 and 01201463334)

Peculiar magnetocaloric properties and critical behavior in antiferromagnetic Tb3Ni with complex magnetic structure

A study on the magnetocaloric properties of a Tb3Ni single crystal (which crystallizes in the orthorhombic Pnma space group) has been undertaken and combined with the study of the character and critical behavior of its magnetic transitions. It presents two important magnetocaloric effects in the temperature range 3–90 K due to the richness and variety of its temperature and magnetic field induced phase transitions. There is a conventional (direct) magnetocaloric effect with a maximum at 65 K and very competitive properties:  = 16.6 J/kgK, RCFWHM = 432 J/kg, with a 50 K span, for μ0ΔH = 5 T, which is due to the transition from a magnetically ordered state to the paramagnetic (PM) state with a combined antiferromagnetic to ferromagnetic (AFM-FM) metamagnetic transition. Besides, it also presents an inverse magnetocaloric effect at very low temperature for which the presence of metamagnetic transitions between AFM and FM states is responsible (=19.9 J/kgK, RCFWHM = 245 J/kg, with a 15 K span, for μ0ΔH = 5 T). At low field (<2 T), the character of the AFM-PM transition which takes place at ≈ 61 K has been well established to be second order and governed by short range order interactions, as the critical parameters α, A+/A- obtained from the specific heat at μ0H = 0 T point to the 3D-Heisenberg universality class. Conversely, the metamagnetic transitions between AFM and FM states, which appear for magnetic fields higher than 2 T, have a first order character, as proved by the magnetization behavior as a function of field and temperature. These properties make this material extremely interesting for magnetic refrigeration applications in the gas liquefaction range 4–77 K.This work has been supported by Universidad del País Vasco UPV/EHU (GIU16/93). A. Herrero thanks the Department of Education of the Basque Government as grantee of the programme “Programa Predoctoral de Formación de Personal Investigador No Doctor”. The authors thank for technical and human support provided by SGIker of UPV/EHU. This work was also supported by Russian Science Foundation (project No. 18-72-10022)

Comprehensive study of the magnetic phase transitions in Tb3Co combining thermal, magnetic and neutron diffraction measurements

A comprehensive study of the magnetic phase transitions in Tb3Co has been undertaken combining different techniques. Using single crystal neutron diffraction in the paramagnetic state a weak crystal structure distortion from the room temperature orthorhombic structure of the Fe3C type described with the Pnma space group toward structure with lower symmetry has been observed with cooling below 100 K. At 81 K there is a second order phase transition to an antiferromagnetic incommensurate phase with the propagation vector k = (0.155, 0, 0). As derived from thermal diffusivity measurements, the critical exponents for this transition are very close to the 3D-Heisenberg universality class, proving that the magnetic interactions are short-range but with a deviation from perfect isotropy due to crystal field effects. At T2 ≈ 70 K there is another magnetic phase transition to a ferromagnetic state whose character is shown to be weakly first order. The low temperature magnetic state has a non-coplanar ferromagnetic structure with strong ferromagnetic components of Tb magnetic moments along the crystallographic c-axis. The application of an external magnetic field B = 2 T along the c crystallographic axis suppresses the incommensurate antiferromagnetic phase and gives rise to the ferromagnetic phase. The magnetic entropy peak change as well as the refrigerant capacity indicate that Tb3Co is a competitive magnetocaloric material in this temperature range. © 2019 Elsevier Lt