Ordered spin-ice state in the geometrically frustrated metallic ferromagnet Sm₂Mo₂O₇

Abstract

The recent discovery of spin ice is a spectacular example of the non-coplanar spin arrangements that can arise in the pyrochlore A₂B₂O₇ structure. We present magnetic and thermodynamic studies on the metallic ferromagnet pyrochlore Sm₂Mo₂O₇. Our studies, carried out on oriented crystals, suggest that the Sm spins have an ordered spin-ice ground state below about T*=15 K. The temperature and field evolution of the ordered spin-ice state are governed by an antiferromagnetic coupling between the Sm and Mo spins. We propose that as a consequence of a robust feature of this coupling, the tetrahedra aligned with the external field adopt a "1-in, 3-out" spin structure as opposed to the "3-in, 1-out" structure in dipolar spin ices, as the field exceeds a critical value.