The magnetic properties of the ferromagnetic-ferromagnetic-antiferromagnetic trimerized spin-1/2 Heisenberg chain are studied theoretically. The high temperature susceptibilty and the ground state saturation magnetic field are calculated and the exchange energies of the trimer compound 3CuCl${ }_2\cdot$2dx are determined. The magnetization curve is obtained by numerical diagonalization of finite size systems. The result explains the low temperature magnetization data for 3CuCl${ }_2\cdot$2dx with the exchange energies obtained as above. It is predicted that the magnetization curve has a plateau at 1/3 of the saturation magnetization if the ferromagnetic exchange energy is comparable to or smaller than the antiferromagnetic exchange energy.
Categories: cond-mat