Tunable magnetism and large inverse magnetocaloric effect in Shastry-Sutherland compounds Tb2Be2Si1-xGexO7 (0 ≤ x ≤ 1)

Abstract

The structure, magnetism and magnetocaloric effect (MCE) have been systematically investigated on the series of Tb2Be2Si1-xGexO7 (0 ≤ x ≤ 1) compounds, where the magnetic Tb3+ ions are located on the quasi-two-dimensional Shastry−Sutherland-Lattice (SSL). The X-ray diffraction measurements reveal that all compounds crystallize into the tetragonal structure with space group P4¯21m, the lattice parameters and nearest neighbor Tb-Tb distances increase monotonically with the variation of doping content x. All samples show the antiferromagnetic (AFM) ordered ground state and field (μ0H) induced spin-flop (SP) transitions below Néel temperature (TN). Moreover, the constructed field-temperature (μ0H−T) phase diagrams of Tb2Be2Si1-xGexO7 (0 ≤ x ≤ 1) reveal that the AFM phase shifts to the low temperature and low field sides with increased x. Below TN, we can observe a crossover behavior of MCE from the low-field (Δμ0H<2.58 T) inverse MCE (IMCE) to the CMCE at high fields (Δμ0H>2.58 T). Among these serial compounds, Tb2Be2SiO7 exhibits the maximal IMCE with a value of 8.30 J kg−1 K−1 under Δμ0H= 0.7 T and 2 K, comparable to the MCE (8.6 J kg−1 K−1) of the benchmark material Tb3Ga5O12 at Δμ0H = 2 T. Additionally, it has a slightly better MCE performance than the materials RE3Ga5O12 (RE = Dy, Tb, Gd) under Δμ0H = 2 T. The realization of large IMCE performance for Tb2Be2SiO7 provides an alternative route for magnetic refrigeration at low field and liquid Helium temperatures.