Magnetic anisotropy in AnTGa5 single crystals

We have investigated oriented single crystals of the antiferromagnets NpCoGa5 (T-N approximate to 47K) and NpRhGa5 (T-N approximate to 36K) and the superconductors PuCoGa5 (T-c approximate to 18 K) and PuRhGa5 (T-c approximate to 9 K) by magnetization and specific heat measurements. Significant anisotropy effects are observed : when magnetic fields are applied in the basal plane. the Neel temperatures of NpCoGa5 and NpRhGa5 are barely affected. On the contrary, in fields applied along the c-axis, NpCoGa5 undergoes a metamagnetic transition to an induced ferromagnet and in NpRhGa5 the second-order transition (magnetic ordering) is shifted to lower temperatures and merges into the first-order transition (reorientation of the magnetic moments). This study reveals the analogy in AnTGa(5) compounds between antiferromagnetic order and superconductivity that are both more fragile when the magnetic field is applied along the c-axis, consistent with antiferromagnetic fluctuations mediated superconductivity in PuCoGa5 and PuRhGa5. (c) 2006 Elsevier B.V. All rights reserved.