Magnetic ground states and magnetodielectric effect in RCr(BO3)2 (R= y and Ho)

The layered perovskites RCr(BO3)2 (R=Y and Ho) with magnetic triangular lattices were studied by performing ac/dc susceptibility, specific heat, elastic and inelastic neutron scattering, and dielectric constant measurements. The results show (i) both samples' Cr3+ spins order in a canted antiferromagnetic structure with TN around 8-9 K, while the Ho3+ ions do not order down to T=1.5 K in HoCr(BO3)2; (ii) when a critical magnetic field HC around 2-3 T is applied below TN, the Cr3+ spins in the Y compound and both the Cr3+ and Ho3+ spins in the Ho compound order in a ferromagnetic state; (iii) both samples exhibit dielectric constant anomalies around the transition temperature and critical field, but the Ho compound displays a much stronger magnetodielectric response. We speculate that this is due to the magnetostriction, which depends on both the Cr3+ and the Ho3+ ions' ordering in the Ho compound. Moreover, by using linear spin-wave theory to simulate the inelastic neutron scattering data, we estimated the Y compound's intralayer and interlayer exchange strengths as ferromagnetic J1=-0.12 meV and antiferromagnetic J2=0.014 meV, respectively. The competition between different kinds of superexchange interactions results in the ferromagnetic intralayer interaction.