Magnetic short-range order and Griffiths-like phase in the S-1/2 spin-dimer ferromagnet BaCu(SeO3)2

Abstract

The polycrystals of S = 1/2 spin-dimer compound BaCu(SeO3)2 have been synthesized by using solid-state reaction. Without long-range order, the magnetic susceptibility χ(T) curve presents two anomalies at T1 = 5 K and TG = 58 K due to antiferromagnetic (AFM) short-range order and short-range ferromagnetic (FM) correlations, respectively, which is further supported by the specific heat and electron spin resonance data. The high-temperature χ(T) curve follows the Curie-Weiss law with θCW = 11.3 K, showing the dominant intradimer FM interaction. The magnetization M(H) curve at 2 K is characteristic of an AFM-FM transition at 0.4 T, suggesting the weak interdimer AFM couplings. The density function theory calculations and quantum Monte Carlo simulations allow an estimation of the intradimer and interdimer exchanges with J1/kB = 39.09 K, J2/kB = −1.51 K, and J3/kB = −1.68 K. Interestingly, the χ−1(T) curve within θCW <T <TG deviates downward from paramagnetic Curie-Weiss behavior, mimicking the Griffiths-like phase. This is further supported by the ac magnetic susceptibility and magnetic relaxation measurements. The competing intradimer FM and interdimer AFM exchanges with a subtle ratio between them are proposed to be responsible for the formation of Griffiths-like phase.