Coupling between Charge Density Wave Ordering and Magnetism in Ho₂Ir₃Si₅

Abstract

Ho 2 Ir 3 Si 5 belongs to the family of three-dimensional (3D) R 2 Ir 3 Si 5 (R = Lu, Er, Ho) compounds that exhibit a first-order, charge-density-wave (CDW) phase transition, where there is a strong orthorhombic-to-triclinic distortion of the lattice accompanied by superlattice reflections. The analysis by single-crystal X-ray diffraction (SXRD) has revealed that the Ir−Ir zigzag chains along c are responsible for the CDW in all three compounds. The replacement of the rare earth element from nonmagnetic Lu to magnetic Er or Ho lowers T CDW , where T CDWLu = 200 K, T CDWEr = 150 K, and T CDWHo = 90 K. Out of the three compounds, Ho 2 Ir 3 Si 5 is the only system where second-order superlattice reflections could be observed, indicative of an anharmonic shape of the modulation wave. The CDW transition is observed as anomalies in the temperature dependencies of the specific heat, electrical conductivity, and magnetic susceptibility, which includes a large hysteresis of 90 to 130 K for all measured properties, thus corroborating the SXRD measurements. Similar to previously reported Er 2 Ir 3 Si 5 , there appears to be a coupling between CDW and magnetism such that the Ho 3+ magnetic moments are influenced by the CDW transition, even in the paramagnetic state. Moreover, earlier investigations on polycrystalline material revealed antiferromagnetic (AFM) ordering at T N = 5.1 K, whereas AFM order is suppressed and only the CDW is present down to at least 0.1 K in our highly ordered single crystal. First-principles calculations predict Ho 2 Ir 3 Si 5 to be a metal with coexisting electron and hole pockets at the Fermi level. The Ho and Ir atoms have spherically symmetric metallic-type charge density distributions that are prone to CDW distortion. Phonon calculations affirm that the Ir atoms are primarily responsible for the CDW distortion, which is in agreement with the experiment.

Much more to explore with an oxidation state of nearly four: Pr valence instability in intermetallic m -Pr 2 Co 3 Ge 5

“…Intrigued by the unstable electronic states and polymorphism in the group 9 germanides (31)(32)(33)(34)(35), we recently showed that large single crystals of both m-Pr 2 Co 3 Ge 5 (Lu 2 Co 3 Si 5 type, I2/c) (36) and o-Pr 2 Co 3 Ge 5 (U 2 Co 3 Si 5 type, Ibam) (37) can be stabilized at room temperature. In this work, we reveal a second-order structural phase transition between two polymorphs of Pr 2 Co 3 Ge 5 through complementary in situ powder x-ray diffraction (PXRD) and in situ electron energy-loss spectroscopy (EELS).…”

Room Temperature Charge Density Wave in a Tetragonal Polymorph of Gd2Os3Si5 and Study of Its Origin in the RE2T3X5 (RE = Rare Earth, T = Transition Metal, X = Si, Ge) Series

“…The magnetic susceptibility χ( T ) reveals an antiferromagnetic (AFM) ordering at T N ∼ 5.5 K, and in the paramagnetic state, it exhibits hysteresis where the CDW transition is observed. The previous results of RE 2 T 3 X 5 compounds have revealed that the dimensionality plays a key role in the formation of the CDW phase. ,− ,− A criterion is proposed, which is based on the lattice parameters according to the value of c / a b , where a , b , and c are the lattice parameters of the tetragonal or orthorhombic structure. We found that 0.526 < c / a b < 0.543 needs to be fulfilled for the existence of a CDW state in a compound of the series of RE 2 T 3 X 5 .…”

“…A gap opens up in the electronic density of states (EDOS), which is often reflected in the physical properties, such as the electrical resistivity and magnetic susceptibility, and in spectroscopic experiments. ,,,, There are various techniques to probe the CDW state, such as X-ray diffraction (XRD), , scanning tunneling microscopy (STM), , transmission electron microscopy (TEM), angle-resolved X-ray photoelectron spectroscopy (ARPES), nuclear magnetic resonance (NMR), Raman spectroscopy, and ultrafast pump–probe experiments . A metal-to-insulator transition (MIT), obvious in the electrical resistivity, together with the appearance of superlattice reflections in XRD are the typical characteristic features pointing toward a CDW state. ,,− …”

“…CDW transitions have been observed for compounds with either structure type. For example, Ramakrishnan et al − reported CDW transitions in three orthorhombic compounds RE 2 Ir 3 Si 5 , with transition temperatures T CDW = 90 K for RE = Ho, T CDW = 150 K for RE = Er, and T CDW = 200 K for RE = Lu. Moreover, Ho 2 Ir 3 Si 5 shows a coupling between CDW ordering and magnetism .…”

“…For example, Ramakrishnan et al − reported CDW transitions in three orthorhombic compounds RE 2 Ir 3 Si 5 , with transition temperatures T CDW = 90 K for RE = Ho, T CDW = 150 K for RE = Er, and T CDW = 200 K for RE = Lu. Moreover, Ho 2 Ir 3 Si 5 shows a coupling between CDW ordering and magnetism . XRD studies pointed toward zigzag chains of Ir atoms being responsible for the stabilization of the CDW in these compounds. − Bugaris et al have reported CDW transitions in the tetragonal compounds RE 2 Ru 3 Ge 5 ( RE = Pr, Sm, Dy), with T CDW = 200 K for RE = Pr, and T CDW = 175 K for RE = Sm.…”