Transverse and Longitudinal Magnetic-Field Responses in the Ising Ferromagnets URhGe, UCoGe and UGe2

The field dependence of the electronic specific heat gamma(H) of URhGe is determined using temperature-dependent magnetization measurements and Maxwell's relation for all three orthorhombic directions. A large (40 %) enhancement of gamma(H) is found at the reorientational transition for fields applied along the b hard axis, which we argue occurs when the field-induced moment is of the same size as the zero-field ordered moment M0. Fields applied along the easy direction, on the other hand, lead to a rapid suppression of gamma(H). We emphasize that this behavior is also applicable to the closely related ferromagnetic superconductors UCoGe and UGe2 and discuss implications for the novel field-induced/enhanced superconductivity in these materials.