Local-Ising-type magnetic order and metamagnetism in the rare-earth pyrogermanate Er2Ge2O7

Abstract

The recent discoveries of proximate quantum spin-liquid compounds and their potential application in quantum computing informs the search for new candidate materials for quantum spin-ice and spin-liquid physics. While the majority of such work has centered on members of the pyrochlore family due to their inherently frustrated linked tetrahedral structure, the rare-earth pyrogermanates also show promise for possible frustrated magnetic behavior. With the familiar stoichiometry RE 2Ge2O7, these compounds generally have tetragonal symmetry with a rare-earth sublattice built of a spiral of alternating edge and corner sharing rare-earth site triangles. Studies on Dy2Ge2O7 and Ho2Ge2O7 have shown tunable low temperature antiferromagnetic order, a high frustration index and spin-ice like dynamics. Here we use neutron diffraction to study magnetic order in Er2Ge2O7 (space group P 41212) and find the lowest yet Neél temperature in the pyrogermanates of 1.15 K. Using neutron powder diffraction we find the magnetic structure to order with k = (0, 0, 0) ordering vector, magnetic space group symmetry P 4 1 212 and a refined Er moment of m = 8.1µB -near the expected value for the Er 3+ free ion. Provocatively, the magnetic structure exhibits similar 'local Ising' behavior to that seen in the pyrocholres where the Er moment points up or down along the short Er-Er bond. Upon applying a magnetic field we find a first order metamagnetic transition at ∼ 0.35 T to a lower symmetry P 2 1 2 1 2 structure. This magnetic transition involves an inversion of Er moments aligned antiparallel to the applied field describing a class I spin-flip type transition, indicating a strong local anisotropy at the Er site -reminiscent of that seen in the spin-ice pyrochlores.

Observation of a Large Magnetic Anisotropy and a Field-Induced Magnetic State in SrCo(VO4)(OH): A Structure with a Quasi One-Dimensional Magnetic Chain

“…Therefore, a versatile synthetic method is essential for obtaining clean samples and large single crystals of mineral-based compounds. Consequently, we use a high-temperature high-pressure solution-based technique to access these mineralogically inspired magnetic materials and other interesting related low-dimensional magnetic materials. ,− Recently, we have been devoting our attention to transition metal vanadates. In contrast to phosphate (PO 4 3– ) and arsenates (AsO 4 3– ), vanadium can possess several oxidation states, including V 3+ ( S = 1) and V 4+ ( S = 1 / 2 ) in addition to the nonmagnetic V 5+ .…”

Linking emergent phenomena and broken symmetries through one-dimensional objects and their dot/cross products

“…Linear magnetoelectricity along z in Cr 2 O 3 , which we discussed earlier, is one example, and further examples of our approach using the tables of dot and cross products, practically handy for the discovery of new phenomena in low-symmetry materials, are discussed in the following. 'toroidal moment + a canted moment', and 'magnetic quadrupole moment + alternating canted moments', respectively, and all have SOS with C. Helical spin states have been observed in numerous magnets such as centrosymmetric compounds such as YMn 6 Sn 6 [20] Gd 2 PdSi 3 [21], MnP [22], and some rare earth metals [23] and crystallographically-chiral compounds such as Co 7 Zn 7 Mn 6 [24], MnSi [25], MnGe [26], Fe 1−x Co x Si [27] with B20 structure, Cu 2 OSeO 3 [28], Cr 1/3 TaS 2 [29], etc 'toroidal moment + a canted moment' has been observed in crystallographically-chiral BaCoSiO 4 [30], and 'magnetic quadrupole moment + alternating canted moments', has been reported in crystallographicallychiral Pb(TiO)Cu 4 (PO 4 ) 4 [31] and Er 2 Ge 2 O 7 [32]. Note that both helical spin state and 'toroidal moment + a canted moment' are 1D objects, and belong to C, but 'magnetic quadrupole moment + alternating canted moments' is 1D objects and belong to C. It turns out that circularly polarized light and vortex light beams with orbital angular momentum are, in fact, chiral (i.e.…”

Reddish-orange emitting Eu2−x Gd x Ge2O7 pyrogermanate ceramic phosphors: synthesis and role of Eu3+/Gd3+ substitution on the optical features

“…Nowadays, RE 2 X 2 O 7 (RE = Y, Sc, La-Lu, X = Ti, Zr, Hf, Si, Ge, Sn) ceramics have gained notoriety in the development of new smart materials due to their interesting and unique properties for the wide application potentialities in strategic scientific areas. Although they have been explored since the 60's [1,2] due to their chemical versatility, recently a growing number of publications have been registered, focusing on luminescent [3][4][5][6] and magnetic [7][8][9][10] properties, as well as catalytic applications [11], that ultimately depend on the crystalline and electronic structures.…”

“…Pyrogermanate-type compounds are less investigated than the majority of RE 2 X 2 O 7 materials. However, lately, they have been investigated mainly due to their interesting magnetic behavior [7][8][9][10]30] and remarkable thermal stability [30][31][32]. Currently, in a set of works for the RE 2 Ge 2 O 7 (RE = La, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu) complete series of ceramics, Martins et al [28,30,33] were the pioneers in reporting alternative conditions of synthesis via moltensalt process saving energy.…”