A Novel Ordered Phase in SrCu2(BO3)2 under High Pressure

TL;DR

This study reveals a new ordered magnetic phase in SrCu2(BO3)2 under high pressure, characterized by symmetry breaking and a doubled unit cell, indicating complex magnetic behavior in this frustrated spin system.

Contribution

The paper reports the discovery of a novel ordered phase in SrCu2(BO3)2 under high pressure, identified through NMR and susceptibility measurements, with evidence of symmetry breaking and unit cell doubling.

Findings

Magnetic phase transition occurs below 3.6 K at high pressure.

Symmetry breaking observed in NMR lines splitting below 30 K.

Low-temperature phase has a doubled unit cell with mixed dimer states.

Abstract

We report results of 11B NMR and susceptibility measurements on the quasi 2D frustrated dimer spin system SrCu2(BO3)2 under high pressure. At 2.4 GPa and in a magnetic field of 7 T, NMR lines split with decreasing temperature in two steps. A gradual splitting below T=30 K breaking the four-fold symmetry of magnetic response is followed by a further sudden splitting below 3.6 K. The latter indicates a magnetic phase transition, which is also marked by a kink in the susceptibility at 1.44 GPa. From the magnetic hyperfine shift data, we conclude that the low-T phase has a doubled unit cell containing two types of dimers, one in a nearly singlet state and the other with a finite magnetization down to T=0.