Aspects of the magnetic structure of TmCu₂

An investigation has been made, using neutron diffraction, of the temperature dependence of the complex magnetic behaviour of TmCu2 in its ordered states. The samples were mainly powdered, but some aspects have also been tested by single-crystal measurements. TmCu2 shows at least three different antiferromagnetic structures in its ordered state. Within these phases, the magnetic structures show a strong ferromagnetic coupling of the moments of next-neighbour Tm atoms in the b direction. The low-temperature structure (AFI) is composed by the first two odd harmonics of a propagation vector (2 pi /8)a*, where the strongest magnetic intensity is caused by the third harmonic. The first phase transition occurs close to 3.1 K. The phase that develops here is a mixture of two structures (AFII).