Double perovskite iridates $A_2$ZnIrO$_6$ ($A$ = alkaline or lanthanide) show complex magnetic behaviors ranging from weak ferromagnetism to successive antiferromagnetic transitions. Here we report the static ($dc$) and dynamic ($ac$) magnetic susceptibility, and neutron powder diffraction measurements for $A$ = La and Nd compounds to elucidate the magnetic ground state. Below 10~K, the $A$ = La compound is best described as canted iridium moments in an antiferromagnet arrangement with a propagation vector \textbf{k} = 0 and a net ferromagnetic component along the $c$-axis. On the other hand, Nd$_2$ZnIrO$_6$ is described well as an antiferromagnet with a propagation vector \textbf{k} = (1/2~1/2~0) below $T_\mathrm{N} \sim$ 17 K. Scattering from both the Nd and Ir magnetic sublattices were required to describe the data and both were found to lie almost completely within the $ab$-plane. $Dc$ susceptibility revealed a bifurcation between the zero-field-cooled and field-cooled curves below $\sim$13 K in Nd$_2$ZnIrO$_6$. A glassy state was ruled out by $ac$ susceptibility but detailed magnetic isotherms revealed the opening of the loop below 13~K. These results suggest a delicate balance exists between the Dzyaloshinskii-Moriya, crystal field schemes, and $d$-$f$ interaction in this series of compounds.
We have successfully synthesized the novel antiferromagnets with Ir$^{4+}$ honeycomb lattice ZnIrO$_3$ and MgIrO$_3$ and investigated their magnetic and thermodynamic properties. The two iridates are isomorphic but exhibit qualitatively different magnetic properties. ZnIrO$_3$ shows antiferromagnetic ordering below 46.6 K, whereas MgIrO$_3$ displays weak ferromagnetic behavior below 31.8 K owing to formation of a canted antiferromagnetic ordering. The measurement of magnetic susceptibility with using an oriented powder sample revealed the presence of an XY-like magnetic anisotropy and a tiltin…
In this work, we report on the synthesis and magnetic properties of a series of double perovskites Ln$_2$ZnIrO$_6$ with Ln = Nd, Sm, Eu & Gd. These compounds present new examples of the rare case of double perovskites (general formula A$_2$BB'O$_6$) with a magnetic 4f -ion on the A-site in combination with the strongly spin-orbit coupled 5d-transition metal ion Ir$^{4+}$ on the B-sublattice. We discuss the impact of different rare earths on the macroscopic magnetic properties. Gd$_2$ZnIrO$_6$ and Eu$_2$ZnIrO$_6$ show weak canted antiferromagnetic order below T$_N$ = 23 K and T$_N$ = 12 K, resp…
Sr$_{3}$ZnIrO$_{6}$ is an effective spin one-half Mott insulating iridate belonging to a family of magnets which includes a number of quasi-one dimensional systems as well as materials exhibiting three dimensional order. Here we present the results of an extensive investigation into the magnetism including heat capacity, a.c. susceptibility, muon spin rotation ($μ$SR), neutron diffraction and inelastic neutron scattering on the same sample. It is established that the material exhibits a transition at about $17$ K into a three-dimensional antiferromagnetic structure with propagation vector $\bo…
We present a combined neutron and synchrotron powder diffraction study of the crystal and magnetic structure of VOCl. The occurrence of antiferromagnetic order in VOCl is accompanied by a monoclinic distortion. The high sensitivity of the magnetic interaction parameters on V-O-V bond angles and V-V distances yields strong magnetoelastic coupling which implies the structural distortion below T$_N$ as well as anomalous structural effects in the paramagnetic phase.
Soft X-ray resonant powder diffraction has been performed at the Mn L2,3 edges of A-site ordered SmBaMn2O6. The energy and polarization dependence of the (1/2 1/2 0) reflection provide direct evidence for a (x2-z2)/(y2-z2) type orbital ordering in contrast to the single layer manganite. The temperature dependence of the reflection indicates an orbital reorientation transition at 210 K, below which the charge and orbital ordered MnO2 sheets show AAAA type of stacking. The concurring reduction of the ferromagnetic super exchange correlations leads to further charge localization.
Rb2SnCu3F12 has been studied using synchrotron powder X-ray diffraction, powder neutron diffraction and single crystal X-ray diffraction at a range of temperatures (100 to 500 K). A broad but clear phase transition, possibly of re-entrant character, is found to occur in the powder form, whereas the corresponding transition is not seen in the single crystal.
Insulating 5d3 La3OsO7 and hole doped La2.8Ca0.2OsO7 materials featuring well separated pseudo-one-dimensional zig-zag chains of corner-sharing OsO6 octahedra have been synthesized and their magnetic and electrical transport properties characterized. Long range magnetic order between the antiferromagnetic chains is determined with a propagation vector k = 1/2, 1/2, 0 and TN = 45 and 53 K for the parent and doped materials. An Os5+ moment of 1.7(1) μB for La3OsO7 and 1.2(2) μB for La2.8Ca0.2OsO7 is refined. The long range magnetic structure is compared to the few currently known for isostructur…
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 present the low-temperature magnetic structures of SrGd$_2$O$_4$ combining neutron diffraction methods on polycrystalline and single-crystal samples containing the $^{160}$Gd isotope. In contrast to other members of the Sr$Ln_2$O$_4$ family ($Ln$ = lanthanide) this system reveals two long-range ordered magnetic phases, which our diffraction data unambiguously identify. Below $T_{\rm N1}$ = 2.73~K, a $\mathbf{q}_1$ = (0 0 0) magnetic structure is stabilized where ferromagnetic chains along the $c$~axis (space group $Pnam$) are coupled antiferromagnetically with neighboring chains. On cooling…
The crystal and magnetic structure of (La0.70Ca0.30)(CryMn1-y)O3 for y = 0.70, 0.50 and 0.15 has been investigated using neutron powder diffraction. The three samples crystallize in the Pnma space group at both 290 K and 5 K and exhibit different magnetic structures at low temperature. In (La0.70Ca0.30)(Cr0.70Mn0.30)O3, antiferromagnetic order with a propagation vector k = 0 sets in. The magnetic structure is Gx, i.e. of the G-type with spins parallel to the a-axis. On the basis of our Rietveld refinement and the available magnetisation data, we speculate that only Cr3+ spins order, whereas Mn…
The discovery of superconductivity in the 122 iron selenide materials above 30 K necessitates an understanding of the underlying magnetic interactions. We present a combined experimental and theoretical investigation of magnetic and semiconducting Ce$_{2}$O$_{2}$FeSe$_{2}$ composed of chains of edge-linked iron selenide tetrahedra. The combined neutron diffraction and inelastic scattering study and density functional calculations confirm the ferromagnetic nature of nearest-neighbour Fe -- Se -- Fe interactions in the ZrCuSiAs-related iron oxyselenide Ce$_{2}$O$_{2}$FeSe$_{2}$. Inelastic measur…
The magnetic ground state of polycrystalline Néel skyrmion hosting material GaV$_4$S$_8$ has been investigated using ac susceptibility and powder neutron diffraction. In the absence of an applied magnetic field GaV$_4$S$_8$ undergoes a transition from a paramagnetic to a cycloidal state below 13~K and then to a ferromagnetic-like state below 6~K. With evidence from ac susceptibility and powder neutron diffraction, we have identified the commensurate magnetic structure at 1.5 K, with ordered magnetic moments of $0.23(2)~μ_{\mathrm{B}}$ on the V1 sites and $0.22(1)~μ_{\mathrm{B}}$ on the V2 site…
The magnetic ground state of two isostructural coordination polymers (i) the quasi two-dimensional S = 1/2 square-lattice antiferromagnet [Cu(HF$_{2}$)(pyrazine)$_{2}$]SbF$_{6}$; and (ii) a new compound [Co(HF$_{2}$)(pyrazine)$_{2}$]SbF$_{6}$, were examined with neutron powder diffraction measurements. We find the ordered moments of the Heisenberg S = 1/2 Cu(II) ions in [Cu(HF$_{2}$)(pyrazine)$_{2}$]SbF$_{6}$ are 0.6(1)$μ_{B}$, whilst the ordered moments for the Co(II) ions in [Co(HF$_{2}$)(pyrazine)$_{2}$]SbF$_{6}$ are 3.02(6)$μ_{B}$. For Cu(II), this reduced moment indicates the presence of …
The crystal and magnetic structures of the spinel compounds ZnCr$_2$S$_4$ and ZnCr$_2$Se$_4$ were investigated by high resolution powder synchrotron and neutron diffraction. ZnCr$_2$Se$_4$ exhibits a first order phase transition at $T_N=21$ K into an incommensurate helical magnetic structure. Magnetic fluctuations above $T_N$ are coupled to the crystal lattice as manifested by negative thermal expansion. Both, the complex magnetic structure and the anomalous structural behavior can be related to magnetic frustration. Application of an external magnetic field shifts the ordering temperature and…
Machine learning magnetic interactions from neutron powder diffraction data
School of Physics, Georgia Institute of Technology（佐治亚理工学院物理学院）；Neutron Scattering Division, Oak Ridge National Laboratory（橡树岭国家实验室中子散射部）；Materials Science and Technology Division, Oak Ridge National Laboratory（橡树岭国家实验室材料科学与技术部）
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…
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…
FeXMn1-XS (0 <x< 0.3) synthesized on the basis of α-MnS are the novel Mott-type substances with the rock salt structure. Neutron diffraction study shows that the shift of the Neel temperature of these materials from 150 (x = 0) to 200 K (x = 0.29) under the action of chemical pressure (x) is accompanied by a decrease in the cubic NaCl lattice parameters. The structural transition with a change in crystal symmetry and a decrease in resistance before the magnetic transition at x = 0.25 is found. Therefore, FeXMn1-XS are interesting materials for both fundamental study of the interrelation betwee…
We report neutron diffraction and transport results on the newly discovered superconducting nitride ThFeAsN with $T_c=$ 30 K. No magnetic transition, but a weak structural distortion around 160 K, is observed cooling from 300 K to 6 K. Analysis on the resistivity, Hall transport and crystal structure suggests this material behaves as an electron optimally doped pnictide superconductors due to extra electrons from nitrogen deficiency or oxygen occupancy at the nitrogen site, which together with the low arsenic height may enhance the electron itinerancy and reduce the electron correlations, thus…
To clarify the magnetic properties of cluster-glass states in Sr1-xLaxRuO3 (0.3 <= x <= 0.5), we report herein the results of muon spin relaxation (muSR) and neutron powder diffraction measurements. The muSR experiments showed that magnetic clusters start developing well above the peak temperature T^* in the ac susceptibility. The volume fraction of the magnetically ordered region increases continuously with decreasing temperature, showing no anomaly at T^*, and reaches nearly 100% at the lowest temperature. The temperature variation of the volume fraction is essentially independent of the La …
We use neutron powder diffraction to study on the non-superconducting phases of ThFeAsN$_{1-x}$O$_x$ with $x=0.15, 0.6$. In our previous results on the superconducting phase ThFeAsN with $T_c=$ 30 K, no magnetic transition is observed by cooling down to 6 K, and possible oxygen occupancy at the nitrogen site is shown in the refinement(H. C. Mao \emph{et al.}, EPL, 117, 57005 (2017)). Here, in the oxygen doped system ThFeAsN$_{1-x}$O$_x$, two superconducting region ($0\leqslant x \leqslant 0.1$ and $0.25\leqslant x \leqslant 0.55$) have been identified by transport experiments (B. Z. Li \emph{e…
We used neutron powder diffraction to obtain the local and long-range structure of La0.5Ca0.5MnO3 at room temperature and 20K. By combining Rietveld and pair distribution function analysis of the total neutron scattering data, we have analyzed the structure of the compound using two competing models describing the low temperature phase: first the charge ordered/orbital ordered model and second the Mn-Mn dimer model. These structural models fit the 20K neutron powder diffraction pattern equally well using Rietveld analysis. Therefore, pair distribution function analysis is used to probe the loc…
Various MSr2YCu2Oz (M1212 with M = Fe, Co, Al and Ga) compounds have been synthesized through a solid state reaction route. All these compounds are derived from the basic CuBa2YCu2O7 structure. Rietveld structural refinement of the room-temperature neutron diffraction data for Fe-1212 reveals that nearly half of Fe remains at the M site, while the other half goes to the Cu site in the CuO2 plane. For the M = Co, Al and Ga compounds, the basic unit cell gets doubled due to two distinct M sites in the M-O layer and the space group Ima2, without any cation intermixing is found more appropriate. F…
We performed magnetic susceptibility and neutron powder diffraction experiments on the ternary compound Pr5Ru3Al2. It belongs to the noncentrosymmetric and nonmirrorsymmetric cubic I213 space group. The previously reported ferromagnetic transition at 24 K was not detected in our improved quality samples. Instead, magnetic ordering was observed in the DC magnetic susceptibility at 3.8 K. Neutron powder diffraction further indicates that an incommensurate magnetic structure is established below 3.8 K, with the magnetic modulation vector (0.066, 0.066, 0.066) (r.l.u.). Using the magnetic represen…
The role of slight changes of the chemical composition on antiferromagnetic ordering of Cr in rare-earth orthochoromites was investigated on a series of ceramic solid-solutions Ce$_{1-x}$Eu${_x}$O$_3$ where x varied from 0 to 1. Gradual replacement of Ce with Eu reduces the cell volume and acts equivalently to applying external pressure. Full replacement of Ce by Eu, on the other hand, reduces the Néel temperature from 260 K for CeCrO$_3$ to 178 K for EuCrO$_3$ as established by magnetization, heat capacity and neutron powder diffraction measurements. High resolution x-ray powder diffraction m…
The development of short- and long-range magnetic order induced in a frustrated zig-zag ladder compound SrDy2O4 by an applied field is studied using neutron diffraction techniques. In zero field, SrDy2O4 lacks long-range magnetic order down to temperatures as low as 60 mK, and the observed powder neutron diffraction (PND) patterns are dominated by very broad diffuse scattering peaks. Single crystal neutron diffraction reveals that the zero-field magnetic structure consists of a collection of antiferromagnetic chains running along the c axis and that there is very little correlation between the…
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 solid solution Cs2-xRbxSnCu3F12 (x = 0, 0.5, 1.0, 1.5) has been investigated crystallographically between 100 and 300 K using synchrotron X-ray powder diffraction and, in the case of x = 0, neutron powder diffraction.
Magnetic and crystal structures of superconducting X yFe 2-xSe 2 (X= Rb and K with Tc=31.5 K and 29.5 K) have been studied by neutron powder diffraction at room temperature. Both crystals show ordered iron vacancy pattern and the crystal structure is well described in the I4/m space group with the lattice constants a=8.799, c=14.576 and a=8.730, c=14.115 A, and the refined stoichiometry x=0.30(1), y=0.83(2) and x=0.34(1), y=0.83(1) for Rb- and K-crystals respectively. The structure contains one fully occupied iron position and one almost empty vacancy position. Assuming that the iron moment is…
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.
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…
