Observation of a High Magnetic Field-Induced Phase Transition in Frustrated Magnet Gadolinium Gallium Garnet

Gadolinium gallium garnet (Gd₃Ga₅O₁₂), or GGG, is a frustrated magnet in which antiferromagnetic exchange interactions exist among Gd³⁺ ions located on two triangular sublattices. The geometric frustration prevents ordering, and the system is best described as a spin liquid at low temperatures. It has been shown that an applied magnetic field of ~1 T produces an antiferromagnetic phase below ~0.4 K, but properties of GGG in higher magnetic fields remain unexplored. Here, we have carried out terahertz magnetospectroscopy measurements on GGG in fields up to 25 T using a table-top pulsed magnet. We performed magnetic field- and temperature-dependent THz transmission measurements and observed a splitting of the electron paramagnetic resonance (EPR) peak for Ga³⁺ ions. Our results indicate that, at high enough magnetic fields and low enough temperatures, there exists a new phase where EPR exhibits two peaks. By taking the 1-peak-to-2-peak transition point as the critical field/temperature, we constructed a phase diagram, which shows a critical magnetic field of ~17 T (~23 T) at 10 K (250 K). We will present a model that takes into account the effect of a strong magnetic field on the antiferromagnetic Gd-Gd exchange interactions on a triangular lattice.