Li4MgReO6: An S=1/2 antiferromagnet exhibiting spin-glass behavior

Abstract

Polycrystalline Li 4 MgReO 6 was prepared by means of solid-state synthesis. The crystallographic structure was determined from high-resolution powder-neutron-diffraction data. It was found that Li 4 MgReO 6 crystallizes in space group C2/m with lattice parameters, aϭ5.0978(3) Å, bϭ8.8163(5) Å, cϭ5.0815(3) Å, and ␤ϭ109.835(2)°. This structure is an ordered variant of Li 2 SnO 3 in which Li ϩ , Mg 2ϩ , and Re 6ϩ ions occupy the Sn 4ϩ sites, which can be desribed as honeycomb layers. Due to the large differences in formal charge, the Re 6ϩ ions order on half of the Sn sites forming a distorted face-shared tetrahedral sublattice. As Re 6ϩ is an Sϭ1/2 ion this material is an attractive candidate for the study of the effects of geometric frustration on a quantum spin system. The investigation of bulk magnetic susceptibilities and magnetization studies as well as low-temperature neutron-diffraction experiments reveals a spin-glass behavior with a glass transition temperature of 12 K. Both heat-capacity and muon spin-relaxation measurements at low temperatures are consistent with a spin-glass interpretation with no long-range order detectable down to Tϭ0.5 K.

Structural and magnetic properties of the5d2double perovskitesSr2BReO6(Aczel1, Zhao2, Calder3 et al. 2016Phys. Rev. B223244View full textAdd to dashboardCite

“…Integrating C mag /T up to the freezing temperature T f = 12 K yields an entropy of 0.18 J/K-mol Re. Although this value represents only 2% of the expected entropy release for an S = 1 spin glass, the drastically-reduced value is consistent with reports of spin glassiness in Sr 2 MgReO 6 (3% entropy release at T f ) [24], Li 4 MgReO 6 (14% entropy release below T f ) [37] and the jarosite (H 3 O)Fe 3 (SO 4 ) 2 (OH) 6 (6% entropy release at T f ) [38]. Furthermore, it is well-known that many spin glasses lose significant entropy above T f [39].…”

“…The low temperature data (T ≤ 20 K) fits well to the function C p = γT + βT 3 with γ = 15.0(1) mJ/K 2 -mol Re and β = 0.774(5) mJ/K 4 -mol Re. A non-zero γ is unexpected in insulators that exhibit magnetic order at low T , and this feature has been interpreted as a signature of spin glass behavior in insulating Sr 2 MgReO 6 [24] and Li 4 MgReO 6 [37]. Therefore, we assume that the linear component represents the magnetic contribution C mag .…”

Geometrically Frustrated Magnetic Materials

“…Two examples which have been studied in some detail are Li 4 MgReO 6 and Li 5 OsO 6 . [30,31] Both involve S ¼ ½ ions, Re 6þ in the former and Os 7þ in the latter. The crystal structure, C2/m, is shown in Figure 2.12.…”

“…30 The magnetic phase diagram for GGG showing the field induced AFLRO state [73]. Reprinted with permission fromSchiffer et al, 1994 [73].…”

Single Crystal Growth of Pure Co3+ Oxidation State Material LaSrCoO4

“…This shows that the nonzero γ term does not arise from an electronic contribution. Thus, it could be attributed to the spin glass state which has a highly degenerate ground state [17,18]. In order to estimate the magnetic contribution C M , the phonon contribution has been subtracted from C p .…”