MODIFICATION OF THE MAGNETIC-FIELD DEPENDENCE OF THE PEIERLS TRANSITION BY A MAGNETIC CHAIN

The magnetic-field dependence of the metal-to-insulator transition tem perature, T-c(B), in the quasi-one dimensional systems (Per)(2)M(mnt)( 2), with M=Au and Pt, was studied by magnetoresistance measurements un der fields up to 18 T. In the Pt compound, our results show that T-c(B ) is anisotropic: T-c(B) decreases as B-2 up to 18 T with a slope simi lar to that found in the Au compound when the magnetic field is applie d parallel to the chain axis, while T-c(B) decreases faster and does n ot follow a pure B-2 dependence when the magnetic field is applied per pendicular to the chain axis. This anisotropy of the field dependence denotes the coupling of the Peierls transition in the perylene chains to a spin-Peierls-like transition in the Pt(mnt)(2)(-) chains, correla ted with an anisotropic magnetic susceptibility, while in the Au compo und a pure Peierls transition takes place.