Recent work analyzing the impact of non-symmorphic symmetries on electronic states has given rise to the discovery of multiple types of topological matter. Here we report the single-crystal synthesis and magnetic properties of EuGa2Sb2, an Eu-based a
ntiferromagnet structurally consisting of pseudo-1D chains of Eu ions related by a non-symmorphic glide plane. We find the onset of antiferromagnetic order at TN = 8 K. Above TN the magnetic susceptibility is isotropic. Curie-Weiss analysis suggests competing ferromagnetic and antiferromagnetic interactions, with peff = 8.1 muB as expected for 4f7 J = S = 7/2 Eu^2+ ions. Below TN and at low applied magnetic fields, an anisotropy develops linearly, reaching chi perpendicular over chi parallel =6 at T = 2 K. There is concomitant metamagnetic behavior along with chi parallel, with a magnetic field of mu0 H=0.5 T sufficient to suppress the anisotropy. Independent of crystal orientation, there is a continuous evolution to a field polarized paramagnetic state with M=7 muB/Eu^2+ cation at mu0 H=2 T as T approaches 0 K. Specific heat measurements show a recovered magnetic entropy of dSmag=16.4 J/mol.K from T near 0 K to T = TN, close to the expected value of Rln(8) for an S = 7/2 ion, indicating negligible low dimensional spin fluctuations above TN. We find no evidence of unusual behaviors arising either from the dimensionality or the presence of the non-symmorphic symmetries.
Recently measurements on various spin-1/2 quantum magnets such as H$_3$LiIr$_2$O$_6$, LiZn$_2$Mo$_3$O$_8$, ZnCu$_3$(OH)$_6$Cl$_2$ and 1T-TaS$_2$ -- all described by magnetic frustration and quenched disorder but with no other common relation -- never
theless showed apparently universal scaling features at low temperature. In particular the heat capacity C[H,T] in temperature T and magnetic field H exhibits T/H data collapse reminiscent of scaling near a critical point. Here we propose a theory for this scaling collapse based on an emergent random-singlet regime extended to include spin-orbit coupling and antisymmetric Dzyaloshinskii-Moriya (DM) interactions. We derive the scaling $C[H,T]/T sim H^{-gamma} F_q[T/H]$ with $F_q[x] = x^{q}$ at small $x$, with $q in$ (0,1,2) an integer exponent whose value depends on spatial symmetries. The agreement with experiments indicates that a fraction of spins form random valence bonds and that these are surrounded by a quantum paramagnetic phase. We also discuss distinct scaling for magnetization with a $q$-dependent subdominant term enforced by Maxwells relations.
With the increased availability of high intensity time-of-flight neutron and synchrotron X-ray scattering sources that can access wide ranges of momentum transfer, the pair distribution function method has become a standard analysis technique for stu
dying disorder of local coordination spheres and at intermediate atomic separations. In some cases, rational modeling of the total scattering data (Bragg and diffuse) becomes intractable with least-squares approaches and necessitates reverse Monte Carlo (RMC) simulations using large supercells. However, the extraction of meaningful information from the resulting atomistic ensembles is challenging, especially at intermediate length scales. We use representational analysis to describe displacements of atoms in RMC ensembles from an ideal crystallographic structure. Rewriting the displacements in terms of a local basis that is descriptive of the ideal crystallographic symmetry provides a robust approach to characterizing medium-range order (and disorder) and symmetry breaking in complex and disordered crystalline materials. This method enables the extraction of statistically relevant displacement modes (orientation, amplitude, and distribution) of the crystalline disorder and provides directly meaningful information in a symmetry-adapted basis set that is most descriptive of the crystal chemistry and physics.
