Anomalous weak ferromagnetism in the magnetically frustrated system R1-xYxB4 (R=Tb and Dy)

Abstract

The magnetic properties of R(1-)x Y x B-4 (R = Tb and Dy) single crystals were investigated. As the concentration of Y increased, the antiferromagnetic transition temperature was observed to systematically decrease, and an exotic weak ferromagnetic transition was also observed at the antiferromagnetic transition temperature. The weak ferromagnetism occurred in the magnetic easy plane, (001) for Tb1-x YxB4, and along the magnetic easy axis, [ 001] for Dy1-xYxB4. For Tb1-xYxB4, the saturated ferromagnetic signal at T = 2 K was also anisotropic, even in the (001) plane; that is, there was a local maximum along the principal axis and a local minimum along the [ 110] axis (equivalent to those along Tb dimers), where the parent compound, TbB4, was characterized as a magnetically frustrated dimer in a Shastry-Sutherland lattice. In addition, the saturated signal exhibited a strong dependence on the Y concentration, i. e., the signal reached amaximum at x = 0.35, indicating that the emergence of the weak ferromagnetism is not due to an individual atomic effect but rather to a collective correlation effect. This is an experimental observation of the development of weak ferromagnetism in a magnetically frustrated system induced by replacing a magnetic element with a nonmagnetic element.