Crystal Growth of Quantum Magnets in the Rare-Earth Pyrosilicate Family R2Si2O7 (R = Yb, Er) Using the Optical Floating Zone Method

Abstract

We report on the crystal growth of rare-earth pyrosilicates, R 2Si 2O 7 for R = Yb and Er using the optical floating zone method. The grown crystals comprise members from the family of pyrosilicates where the rare-earth atoms form a distorted honeycomb lattice. C-Yb 2Si 2O 7 is a quantum dimer magnet with field-induced long range magnetic order, while D-Er 2Si 2O 7 is an Ising-type antiferromagnet. Both growths resulted in multi-crystal boules, with cracks forming between the different crystal orientations. The Yb 2Si 2O 7 crystals form the C-type rare-earth pyrosilicate structure with space group C 2 / m and are colorless and transparent or milky white, whereas the Er-variant is D-type, P 2 1 / b , and has a pink hue originating from Er 3 +. The crystal structures of the grown single crystals were confirmed through a Rietveld analysis of the powder X-ray diffraction patterns from pulverized crystals. The specific heat of both C-Yb 2Si 2O 7 and D-Er 2Si 2O 7 measured down to 50 mK indicated a phase transition at T N ≈ 1.8 K for D-Er 2Si 2O 7 and a broad Schottky-type feature with a sharp anomaly at 250 mK in an applied magnetic field of 0.8T along the c-axis in the case of C-Yb 2Si 2O 7 .

Néel Ordering in the Distorted Honeycomb Pyrosilicate: C-Er$_{2}$Si$_{2}$O$_{7}$

“…We have not been successful in growing single crystals of C-Er 2 Si 2 O 7 via the optical floating zone technique because the high-temperature polymorph, D-Er 2 Si 2 O 7 , is stabilized from the melt instead. 29…”

Optical floating zone crystal growth of rare-earth disilicates, $R\mathbf{_{2}}$Si$\mathbf{_{2}}$O$\mathbf{_{7}}$ ($R=$ Er, Ho, and Tm)

“…The temperature of the sharp feature observed in the heat capacity measurements further demonstrates that the FZ-grown Er 2 Si 2 O 7 crystal belongs to the structural type D, because C-type Er 2 Si 2 O 7 orders below T N = 2.50(5) K. 22,24 The results are in agreement with the previous results published on a Er 2 Si 2 O 7 crystal grown using the FZ method. 16 Extensive studies of the magnetic ground state of D-type Er 2 Si 2 O 7 are described elsewhere in a more detailed paper.…”

“…The successful growth of ytterbium and erbium disilicate crystals using optical FZ method 16 has resulted in a resurgence of interest in the magnetic ground states of these compounds. 17,18 Yb 2 Si 2 O 7 is the first Yb 3+ based material that exhibits a quantum dimer magnet (QDM) state, consisting of nearest neighbour spin dimers, with magnetic field-induced order reminiscent of a Bose-Einstein condensate (BEC) phase.…”

“…There have been many attempts to grow crystals of the rare-earth disilicate compounds. Typical routes used to prepare R 2 Si 2 O 7 crystals include the Verneuil, 19 flux, [20][21][22][23][24][25] Czochralski, 8 chemical vapour transport (CVT), 26 floating zone (FZ) 6,16 and micro-pulling-down (µ-PD) 27 techniques. The FZ method of crystal growth has been widely employed in the past for the growth of oxides, and not only is it the ideal technique to produce large, high quality single crystals, but it is also one of the most appropriate methods due to its advantages compared to the conventional techniques of crystal growth.…”

“…Erbium disilicate exists in three polymorphs (see Table 1), a triclinic (P 1) low temperature phase (referred to as B-type), a monoclinic (C2/m) structure (C-type), and a high temperature monoclinic (P 2 1 /b) arrangement (D-type). grown from the melt, by the FZ method will therefore belong to the structural type D. 16 Due to the arrangement of the magnetic ions in the crystallographic structure, forming a distorted honeycomb-like lattice (see Fig. as well as exhibiting a highly anisotropic magnetic behaviour.…”