Possible classical to quantum transition in spin-chain compounds Gd2−xNdxBaNiO5

A possible classical to quantum transition has been demonstrated by the mixing effects of Gd and Nd in spin-chain compounds Gd2−xNdxBaNiO5. First, the M(T) curves for the Gd-rich compounds exhibit a monotonous increase with decreasing temperature whereas those for the Nd-rich compounds consist of a maximum and minimum structure due to the Gd/Nd and Ni excitations. Second, the 1/χ(T) curves for the Gd-rich compounds demonstrate Curie-Weiss-like behavior, which is absent for the Nd-rich side. It is therefore concluded that the Gd-rich compounds behave totally like classical magnets while the Nd-rich compounds quantum magnets. The enhanced magnetic anisotropy due to the Nd doping is proposed to be responsible for this classical-quantum transition.