NEUTRON-DIFFRACTION STUDY OF RMN4AL8 (R=ND, DY, HO, ER), ERCR4AL8 ANDERCU4AL8

Neutron powder diffraction has been used to investigate the magnetic o rder in a series of RMn(4)Al(8) (space group I-4/mmm) compounds with R = (Nd, Dy, Ho and Er). For compounds with Mn, no magnetic order was d etected down to 1.6K, whilst for the compound ErCr4Al8, two very weak magnetic reflections were observed at 1.6 K. The observed magnetic pea ks cannot be indexed on the tetragonal unit cell, indicating a possibl e incommensurate magnetic structure. For ErCu4Al8, a type 1 antiferrom agnetic structure is observed. The magnitude and temperature dependenc e of the Er3+ magnetic moment can be adequately modelled by a combined isotropic exchange and tetragonal crystal held Hamiltonian within the Mean Field Approximation.