Field-induced partial disorder in a Shastry-Sutherland lattice.

A 2-Q antiferromagnetic order of the ferromagnetic dimers was found below T = 2.9 K in the Shastry-Sutherland lattice BaNdZnS by single crystal neutron diffraction. The magnetic order can be understood by the orthogonal arrangement of local Ising Nd spins, identified by polarized neutrons. A field was applied along [1 -1 0] to probe the observed metamagnetic transition in the magnetization measurement. The field decouples two magnetic sublattices corresponding to the propagation vectors q = (½, ½, 0) and q = (-½, ½, 0), respectively. Each sublattice shows a "stripe" order with a Néel-type arrangement in each single layer. The "stripe" order with q remains nearly intact up to 6 T, while the other one with q is suppressed at a critical field H ~1.7 T, indicating a partial disorder. The H varies with temperature and is manifested in the H-T phase diagram constructed by measuring the magnetization in BaNdZnS.