Intrinsic low field susceptibility in pseudobinary DyxY1-> x> Al2andTbxGd1- xAl2 cubic intermetallic compounds

Low field ( H_ac ≈ 3.5 x 10 ^-6T) and low frequency (15 Hz) ac susceptibilities, χ _i, have been measured between 3.3 K and well above the Curie temperatures, for the intermetallic Laves phase compounds Dy _xY _{1- x}Al ₂ and Tb _xGd _{1- x}Al ₂. It is concluded that χ _i is, at low enough temperatures, dominated by the domain wall excursions around the minima of the anisotropy Peierls potential wells. The derived model relation χ_i( T) H_c^{( i)} ( T) = const., where H _c⁽ⁱ⁾ is the intrin sic pinning coercive field, is confirmed at low enough temperatures. The shape of the observed susceptibility cusps around the Curie temperatures in the series Dy _xY _{1- x}Al ₂ ( x 0.35) suggests that these systems are magnetically inhomogenous. The magnetic domain sizes estimated from these measurements seem quite small (between around 0.01 and 0.1 μm).