Field-Induced Partial Disorder in a Shastry-Sutherland Lattice*

Geometrical frustration in magnetic systems can drive the stabilization of exotic phases such as spin-liquids. The Shastry-Sutherland lattice is one such geometrically frustrated lattice that consists of a two-dimensional orthogonal arrangement of spin dimers and results in rich phase diagrams. In this talk I will present the findings of the possible field-induced spin liquid state of S=1 spin dimers in the Shastry-Sutherland lattice material BaNd₂ZnS₅. A metamagnetic transition in the bulk magnetization measurement was observed under field along the ab plane below T_N = 2.9K. We established the Ising behavior in the Nd spins by the local magnetic susceptibility method with polarized neutrons at the paramagnetic state. The zero-field 2-Q antiferromagnetic order of ferromagnetic dimers was determined by neutrons at 1.4 K. The constituting propagation vectors q₁ = (½ ½ 0) and q₂ = (-½ ½ 0) each exhibit a “stripe” order when viewing multiple layers and a Néel-type arrangement in a single layer. By applying field along [1 -1 0] the two sublattices respond differently. The q₁ magnetic sublattice remains relatively intact up to 6 T while the stripe phase of the q₂ magnetic sublattice order is suppressed at the critical field H_c = 1.7 T, indicating an emerging partial disorder, liquid state of ferromagnetic dimers, corresponding to the metamagnetic transition in the bulk measurement. With this information we constructed an H-T phase diagram from the bulk magnetization measurements that clearly defines the “stripe” state at lower field and a field polarized state at upper fields with a critical region emerging in between represented as a spin dimer liquid phase.