Investigating the Magnetic Properties of Frustrated Spin Systems: Triangular and Square Lattices

Abstract

In the study of magnetic materials, frustration—when there are competing interactions that cannot all be simultaneously satisfied—provides a fruitful playground in the search for new physics. Frustrated materials can have highly degenerate ground state, which can give rise to a variety of new phases. The most coveted of these is the quantum spin liquid, which is a state that resists magnetic order, in which the spins remain dynamic and highly entangled down to very low temperatures. In this work, we present results on three families of rare-earth based spin liquid candidates. Since the rare-earth elements are so chemically similar, they can easily be swapped to study the effects of different spins without significantly affecting the crystal structure of the material. The double borates Ba3RE(BO3)3 (RE = Tb, Ho, Er, Yb) are layered materials with the rare-earth atoms forming triangular lattices, the simplest geometrically frustrated lattice. The melilites RE2Be2GeO7 (RE = Nd, Gd, Yb) form a distorted square lattice known as the Shastry–Sutherland lattice, which has been the subject of intense theoretical interest for the past 40 years. Finally, TmZn2GaO5 is a disorder-free material which also has the Tm sitting on a triangular lattice. We have prepared high-quality powder and single crystal samples of these materials, and investigated their magnetic properties using a variety of experimental probes, including SQUID magnetometry, heat capacity, and neutron scattering measurements. These measurements establish interesting physics in these materials, and serve as a guide for future investigations into their properties.