Magnetic structure study of antiferromagnet NpPtGa5 by neutron diffraction

The magnetic structure of NpPtGa5was investigated by neutron diffraction. NpPtGa5 exhibits an A-type antiferromagnetic structure with propagation vector q→=(0,0,1/2) below TN=26 K. The estimated Np magnetic moment is 0.38(5) μB, and it is oriented parallel to the 〈100〉 direction. This small moment would be consistent with the large γ=123 mJ/(K2 mol), indicative of the heavy fermion nature. The field-induced anomaly in the magnetic susceptibility is clarified to be a signature for an antiferromagnetic domain change between multi-domains to single-domain states.