Commensurate-incommensurate magnetic phase transitions of CePtAl

Abstract

The magnetic properties of CePtAl with orthorhombic TiNiSi-type chemical structure were investigated. Single-crystal experiments of electrical resistivity, specific heat and magnetic susceptibility reveal the existence of three magnetic phase transitions at T1=5.9 K (second order), T2=4.3 K (first order) and T3=2.2 K (first order). Powder neutron diffraction measurements detected complex magnetic structures consisting of two coexisting, partly incommensurate magnetic propagation vectors: k1=0 and k3=(0, 0.463(8), 0) for T2<or=T<or=T1; and k1=0 and k2=(0, 1/2, 0) for T<or=T2. The predominantly ferromagnetic k1 component and the antiferromagnetic k2 component of the magnetic low-temperature structure of CePtAl were refined at 1.5 K. Magnetism in CePtAl is dominated by a ferromagnetic component (1.35(4) mu B at 1.5 K) oriented parallel to the magnetically easy a axis. The complexity of magnetic structures in CePtAl appears to be caused by competing anisotropic magnetic exchange interactions in a network, where Ce-Ce nearest neighbours (3.56 AA) form chains parallel to the b axis and Ce-Ce second-nearest neighbours (3.77 AA) form chains along the a axis.