We present a combined neutron and synchrotron powder diffraction study of the crystal and magnetic structure of VOCl. The occurrence of antiferromagnetic order in VOCl is accompanied by a monoclinic distortion. The high sensitivity of the magnetic interaction parameters on V-O-V bond angles and V-V distances yields strong magnetoelastic coupling which implies the structural distortion below T$_N$ as well as anomalous structural effects in the paramagnetic phase.
We carried out detailed studies of the magnetic structure, magnetoelastic coupling, and thermal properties of EuCrO$_3$ nano-powders from room temperature to liquid helium temperature. Our neutron powder diffraction and X-ray powder diffraction measurements provide precise atomic positions of all atoms in the cell, especially for the light oxygen atoms. The low-temperature neutron powder diffraction data revealed extra Bragg peaks of magnetic origin which can be attributed to a $G_x$ antiferromagnetic structure with an ordered moment of $\sim$ 2.4 $μ_{\rm B}$ consistent with the $3d^3$ electro…
We have studied the temperature dependence of crystal and magnetic structures of the Jahn-Teller distorted transition metal difluorides CrF$_2$ and CuF$_2$ by neutron powder diffraction in the temperature range 2-280 K. The lattice parameters and the unit cell volume show magnetoelastic effects below the Néel temperature. The lattice strain due to the magnetostriction effect couples with the square of the order parameter of the antiferromagnetic phase transition. We also investigated the temperature dependence of the Jahn-Teller distortion which does not show any significant effect at the anti…
Submicron powder of CrO$_2$ was prepared by hydrothermal synthesis method from chromium trioxide. Particles obtained were of rounded form with mean diameter about 120 nm. The powder (stabilized with thin surface layer of β-CrOOH) has been characterized by structural, X-ray and magnetic measurements. The powder (with Curie temperature about 385 K) was cold-pressed and its transport and magnetotransport properties have been measured in the temperature range 4--450 K in magnetic field up to 1.6 T. The samples studied is characterized by non-metallic temperature behavior of resistance and large ne…
Resistive, magnetoresistive and magnetic properties of four kinds of pressed CrO2 powders, synthesized by hydrothermal method of chromic anhydride have been investigated. The particles in powders constituted of rounded particles (diameter 120 nm) or needle-shaped crystals with an average diameter of 22.9 nm and average length of 302 nm. All of the particles had a surface dielectric shell of varying thickness and different types (such as oxyhydroxide -CrOOH or chromium oxide Cr2O3). For all the samples at low temperatures we found non-metallic temperature dependence of resistivity and giant neg…
The crystal structure and the magnetism of BaMn$_2$O$_3$ have been studied by thermodynamic and by diffraction techniques using large single crystals and powders. BaMn$_2$O$_3$ is a realization of a $S = 5/2$ spin ladder as the magnetic interaction is dominant along 180$^\circ$ Mn-O-Mn bonds forming the legs and the rungs of a ladder. The temperature dependence of the magnetic susceptibility exhibits well-defined maxima for all directions proving the low-dimensional magnetic character in BaMn$_2$O$_3$. The susceptibility and powder neutron diffraction data, however, show that BaMn$_2$O$_3$ exh…
Low temperature magnetic and structural behavior of the extended Kagome system YBaCo4O7 has been studied by single crystal neutron diffraction and high-resolution powder X-ray diffraction. Long-range magnetic ordering associated with a structural transition from orthorhombic Pbn2_1 to monoclinic P2_1 symmetry has been found at T_1 ~ 100 K. The interplay between the structural and magnetic degrees of freedom testifies that the degeneracy of the magnetic ground state, present in the orthorhombic phase, is lifted through a strong magnetoelastic coupling, as observed in other frustrated systems. A…
We report temperature dependent magnetization and neutron diffraction measurements on the corundum related magnetoelectric antiferromagnet Mn$_{4}$Ta$_{2}$O$_{9}$. Measurements performed on a single crystalline specimen reveal that the magnetization is anisotropic, and a weak ferromagnetic component emerges well within the antiferromagnetically ordered state. Powder neutron diffraction measurements indicate that the magnetic structure comprises of antiferromagnetically coupled ferromagnetic chains of Mn$^{2+}$ spins aligned along the trigonal $c$ axis, in contrast to that reported in other iso…
We present the discovery and refinement by neutron powder diffraction of a new magnetic phase in the Na1-xCaxMn7O12 quadruple perovskite phase diagram, which is the incommensurate analogue of the well-known pseudo-CE phase of the simple perovskite manganites. We demonstrate that incommensurate magnetic order arises in quadruple perovskites due to the exchange interactions between A and B sites. Furthermore, by constructing a simple mean field Heisenberg exchange model that generically describes both simple and quadruple perovskite systems, we show that this new magnetic phase unifies a picture…
We have investigated the structural and magnetic transitions in CsCoO$_2$ using calorimetric measurements, neutron powder diffraction (NPD), density functional theory (DFT) calculations and muon-spin relaxation ($μ$SR) measurements. CsCoO$_2$ exhibits three-dimensional long-range antiferromagnetic (AFM) order at 424~K, resulting in antiferromagnetic alignment of chains of ferromagnetically ordered Co-Co spin dimers. Although there is no change in magnetic structure around a structural transition at $T^{*}=100$~K, the resulting bifurcation of corner-shared Co--O--Co bond angles causes a weakeni…
We report synchrotron radiation diffraction and muon spin rotation (muSR) measurements on the frustrated pyrochlore magnet Tb2Ti2O7. The powder diffraction study of a crushed crystal fragment does not reveal any structural change down to 4 K. The muSR measurements performed at 20 mK on a mosaic of single crystals with an external magnetic field applied along a three-fold axis are consistent with published a.c. magnetic-susceptibility measurements at 16 mK. While an inflection point could be present around an internal field intensity slightly above 0.3 T, the data barely support the presence of…
The structural properties of BiMn$O_3$ were determined from neutron powder diffraction data as a function of temperature and magnetic field. The structure at all temperatures was found to be centrosymmetric with space group $C2/c$, which is incompatible with ferroelectricity. At T$_C\simeq 100 K$, we observed the onset of a large magnetoelastic strain, proportional to the square of the magnetization. We interpret this structural rearrangement, together with the previously observed magnetodielectric anomalies, as due to the need to optimize the partially frustrated magnetic interactions.
The chiral magneto-electric compound Ni3TeO6 is investigated through temperature-dependent synchrotron-based powder x-ray diffraction and x-ray absorption spectroscopy between 15 to 300 K. Our work provides direct evidence for the exchange-striction in the material around the concomitant onset point of collinear antiferromagnetic and magneto-electric phases. The x-ray absorption near edge spectra and x-ray photoelectron spectra show that the sample consists of both Ni2+ and Ni3+ ions in the lattice. The ionic state of Ni is found to be quite robust, and it is largely independent of the prepara…
Through analysis of variable temperature neutron powder diffraction data, we present solutions for the magnetic structures of SrMn$_7$O$_{12}$, CdMn$_7$O$_{12}$, and PbMn$_7$O$_{12}$ in all long-range ordered phases. The three compounds were found to have magnetic structures analogous to that reported for CaMn$_7$O$_{12}$. They all feature a higher temperature lock-in phase with \emph{commensurate} magneto-orbital coupling, and a delocked, multi-\textbf{k} magnetic ground state where \emph{incommensurate} magneto-orbital coupling gives rise to a constant-moment magnetic helix with modulated sp…
α-SrCr2O4 has a triangular planar lattice of d3 Cr3+ made from edge sharing CrO6 octahedra; the plane shows a very small orthorhombic distortion from hexagonal symmetry. With a Weiss temperature of -596 K and a three-dimensional magnetic ordering temperature of 43 K, the magnetic system is quasi two-dimensional and frustrated. Neutron powder diffraction shows that the ordered state is an incommensurate helical magnet, with an in-plane propagation vector of k = (0,0.3217(8),0). Temperature dependent synchrotron powder diffraction characterization of the structure shows an increase in the inter-…
High resolution X-ray powder-diffraction experiments on a well-characterized polycrystalline sample of the spin liquid Tb2Ti2O7 reveal that it shows normal positive thermal-expansion above 4 K, which does not agree with the intriguing anomalous negative thermal-expansion due to a magneto-elastic coupling reported for a single crystal sample below 20 K. We also performed a Rietveld profile refinement of a powder-diffraction pattern taken at a room temperature, and confirmed that it is consistent with the fully ordered cubic pyrochlore structure.
Through powder x-ray diffraction we have investigated the structural behavior of SmVO3, in which orbital and magnetic degrees of freedom are believed to be closely coupled to the crystal lattice. We have found, contrary to previous reports, that SmVO3 exists in a single, monoclinic, phase below 200 K. The associated crystallographic distortion is then stabilized through the magnetostriction that occurs below 134 K. The crystal structure has been refined using synchrotron x-ray powder diffraction data measured throughout the structural phase diagram, showing a substantial Jahn-Teller distortion…
We have studied the crystal and magnetic structures of Fe-doped hexagonal manganites LuMn1-xFexO3 (x = 0, 0.1, 0.2, and 0.3) by using bulk magnetization and neutron powder diffraction methods. The samples crystalize consistently in a hexagonal structure and maintain the space group P63cm from 2 to 300 K. The Néel temperature TN increases continuously with increasing Fe-doping. In contrast to a single Γ4 representation in LuMnO3, the magnetic ground state of the Fe-doped samples can only be described with a spin configuration described by a mixture of Γ3 (P63'cm') and Γ4 (P63'c'm) representatio…
The polycrystalline samples of LaGa1-xMnxO3 (0<x<0.3) has been prepared by solid state reaction route. The phase purity of these samples has been confirmed by powder x-ray diffraction experiments carried out on BL-12 at Indus-2 synchrotron radiation source. The sample with x=0.2 shows significant change in the value of capacitance with the application of magnetic field. The observed results were understood by systematically analyzing magneto-capacitance (MC), magneto resistance (MR) and dielectric loss as a function of frequency. Our results and analysis suggests that the observed magneto diel…
The Co2V2O7 is recently reported to exhibit amazing magnetic field-induced magnetization plateaus and ferroelectricity, but its magnetic ground state remains ambiguous due to its structural complexity. Magnetometry measurements, and time-of-flight neutron powder diffraction (NPD) have been employed to study the structural and magnetic properties of Co2V2O7, which consists of two non-equivalent Co sites. Upon cooling below the Neél temperature TN = 6.3 K, we observe magnetic Bragg peaks at 2K in NPD which indicated the formation of long range magnetic order of Co2+ moments. After symmetry analy…
We use neutron powder diffraction to investigate the magnetic and crystalline structure of Cr$_2$GaN. A magnetic phase transition is identified at $T \approx 170$ K, whereas no trace of structural transition is observed down to 6 K. Combining Rietveld refinement with irreducible representations, the spin configuration of Cr ions in Cr$_2$GaN is depicted as an incommensurate sinusoidal modulated structure characterized by a propagating vector ${k}$=(0.365, 0.365, 0). Upon warming up to the paramagnetic state, the magnetic order parameter closely resembles to the temperature dependence of $c$-ax…
Orthoferrites are a class of magnetic materials with a magnetic ordering temperature above 600 K, predominant G-type antiferromagnetic ordering of the Fe-spin system and, depending on the rare-earth ion, a spin reorientation of the Fe spin taking place at lower temperatures. DyFeO3 is of particular interest since the spin reorientation is classified as a Morin transition with the transition temperature depending strongly on the Dy-Fe interaction. Here, we report a detailed study of the magnetic and structural properties of microcrystalline DyFeO3 powder and bulk single crystal using neutron di…
High-resolution neutron diffraction determination of noncollinear antiferromagnetic order in the honeycomb magnetoelectric Fe$_{4}$Nb$_{2}$O$_{9}$
Institute for Basic Science (IBS)（韩国基础科学研究院）；Yonsei University（延世大学）；Chonnam National University（全南国立大学）；Center for Integrated Nanostructure Physics, Institute for Basic Science (IBS)（韩国基础科学研究院集成纳米物理中心）；Sungkyunkwan University（成均馆大学）；Rutgers University（罗格斯大学）
Coexistence of mutually influencing ferroelectric and magnetic ordering at low temperature in hexagonal phase of rare-earth manganites gives rise to interesting physical phenomena. Here, we report a detailed analysis of powder neutron diffraction (ND) studies on polycrystalline Y1-xDyxMnO3 (x = 0, 0.05) as a function of temperature. Our analysis shows that Dy doping at Y site leads to modification in lattice constants: unit cell shrinks in c direction, but expands in ab plane, unit cell volume increases and effective Mn magnetic moment also reduces. All the Mn-O bond lengths and O-Mn-O bond an…
Nuclear magnetic resonance (NMR), neutron diffaction (ND), x-ray diffraction, magnetic susceptibility and specific heat measurements on the frustrated A-site spinel CoAl2O4 compound reveal a collinear antiferromagnetic ordering below Tn = 9.8(2) K. A high quality powder sample characterized by x-ray diffraction that indicates a relatively low Co-Al inversion parameter x = 0.057(20) in (Co1-xAlx)[Al2-xCox]O4, shows a broad maximum around 15 K in magnetic susceptibility and a sharp peak at Tn in heat capacity. The average ordered magnetic moment of Co^2+ (S = 3/2) ions at the A-site is estimated…
We report the results of direct measurement of remanent hysteresis loops on nanochains of BiFeO$_3$ at room temperature under zero and $\sim$20 kOe magnetic field. We noticed a suppression of remanent polarization by nearly $\sim$40\% under the magnetic field. The powder neutron diffraction data reveal significant ion displacements under a magnetic field which seems to be the origin of the suppression of polarization. The isolated nanoparticles, comprising the chains, exhibit evolution of ferroelectric domains under dc electric field and complete 180$^o$ switching in switching-spectroscopy pie…
The present work aims to address the electronic and magnetic properties of the intermetallic compound GdPd$_2$Bi through a comprehensive study of the structural, magnetic, electrical and thermal transport on a polycrystalline sample, followed by theoretical calculations. Our findings indicate that the magnetic ground state is antiferromagnetic in nature. Magnetotransport data present prominent hysteresis loop hinting a structural transition with further support from specific heat and thermopower measurements, but no such signature is observed in the magnetization study. Temperature dependent p…
The magnetic structures and the magnetic phase transitions in the Mn-doped orthoferrite TbFeO$_3$ studied using neutron powder diffraction are reported. Magnetic phase transitions are identified at $T^\mathrm{Fe/Mn}_N \approx$ 295~K where a paramagnetic-to-antiferromagnetic transition occurs in the Fe/Mn sublattice, $T^\mathrm{Fe/Mn}_{SR} \approx$ 26~K where a spin-reorientation transition occurs in the Fe/Mn sublattice and $T^\mathrm{R}_N \approx$ 2~K where Tb-ordering starts to manifest. At 295~K, the magnetic structure of the Fe/Mn sublattice in TbFe$_{0.5}$Mn$_{0.5}$O$_3$ belongs to the ir…
The magnetic and structural properties of polycrystalline Co$_{4-x}$ Ni$_x$ Nb$_2$ O$_9$ (x=1,2) have been investigated by neutron powder diffraction, magnetization and heat capacity measurements, and density functional theory (DFT) calculations. For x=1, the compound crystallizes in the trigonal P$\bar{3}$c1 space group. Below T$_N$ = 31 K it develops a weakly non-collinear antiferromagnetig structure with magnetic moments in the ab-plane. The compound with x=2 has crystal structure of the orthorhombic Pbcn space group and shows a hard ferrimagnetic behavior below T$_C$ =47 K. For this compou…
The Ca$_2$MnReO$_6$ double perovskite is a spin-orbit-assisted Mott insulator with exotic magnetic properties, including a largely non-collinear Mn$^{2+}$ spin arrangement and nearly orthogonal coupling between such spins and the much smaller Re $5d$ magnetic moments. Here, the electron-doped compound Ca$_{1.7}$Y$_{0.3}$MnReO$_6$ is investigated. Neutron and X-ray powder diffraction confirm that nearly full chemical order is maintained at the Mn and Re sites under the Y substitution at the Ca site. X-ray absorption measurements and an analysis of the Mn-O/Re-O bond distances show that the Mn o…
Here, we report successful single crystal growth of SnSb2Te4 using the self-flux method. Unidirectional crystal growth is confirmed through X Ray Diffraction (XRD) pattern taken on mechanically cleaved crystal flake while the rietveld refined Powder XRD (PXRD) pattern confirms the phase purity of the grown crystal. Scanning Electron Microscopy (SEM) image and Energy Dispersive X-Ray analysis (EDAX) confirm crystalline morphology and exact stoichiometry of constituent elements. Vibrational Modes observed in Raman spectra also confirm the formation of the SnSb2Te4 phase. DC resistivity measureme…
We present a comprehensive experimental and ab-initio study of the $S=1/2$ Mo$^{5+}$ system, KMoOP$_2$O$_7$, and show that it realizes the $S = 1/2$ Heisenberg chain antiferromagnet model. Powder neutron diffraction reveals that KMoOP$_2$O$_7$ forms a magnetic network comprised of pairs of Mo$^{5+}$ chains within its monoclinic $P2_1/n$ structure. Antiferromagnetic interactions within the Mo$^{5+}$ chains are identified through magnetometry measurements and confirmed by analysis of the magnetic specific heat. The latter reveals a broad feature centred on $T_\textrm{N} = 0.54$ K, which we ascri…
Neutron powder diffraction studies of the crystal and magnetic structures of the magnetocaloric compound Mn1.1Fe0.9(P0.8Ge0.2) have been carried out as a function of temperature, applied magnetic field, and pressure. The data reveal that there is only one transition observed over the entire range of variables explored, which is a combined magnetic and structural transformation between the paramagnetic to ferromagnetic phases (Tc~255 K for this composition). The structural part of the transition is associated with an expansion of the hexagonal unit cell in the direction of the a- and b-axes and…
Probing the magnetic ground state and magnetoelastic coupling in double perovskite ruthenate: Ca2ScRuO6
Indian Institute of Technology Palakkad（印度理工学院帕拉克卡德分校）；Bhabha Atomic Research Centre（巴哈原子研究中心）；Homi Bhabha National Institute（霍米·巴巴国立研究所）；Indian Institute of Technology Kharagpur（印度理工学院卡拉格普尔分校）；UGC-DAE Consortium for Scientific Research（UGC-DAE科学研究联盟）
Double magnetic transition, complex field-induced phases, and large magnetocaloric effect in the frustrated garnet compound Mn$_{3}$Cr$_{2}$Ge$_{3}$O$_{12}$
The magnetic properties of the high temperature alpha form of the CaCr2O4 compound have been investigated for the first time by magnetic susceptibility, specific heat and powder neutron diffraction. The system undergoes a unique magnetic phase transition at 43K to a long range order incommensurate helical phase with magnetic propagation vector k=(0,0.3317(2),0). The magnetic model proposed from neutron diffraction data shows that the plane of rotation of the spins is perpendicular to the wave-vector, and that the magnetic modulation is consistent with two modes belonging to distinct irreducibl…
