EPR study of the two-dimensional molecular composite [NH3-(CH2)5-NH3]CuCl4:: Evidence for both spin diffusion and spin anisotropies

The quasi two-dimensional single crystal [NH3-(CH2)(5)-NH3]CuCl4 has been studied by EPR measurements at X-band, room temperature and T = 100 K in three perpendicular planes (a, b), (a, c*), (b, c*). This compound crystallizes in the monoclinic system with four entities per unit cell. Only one EPR exchange-collapsed line was observed for the four magnetically inequivalent copper ions in the lattice at room temperature. A careful analysis of experimental data permits us to obtain the principal values of the g-factor: g(perpendicular to) = 2.052 and g(parallel to) = 2.267. The EPR linewidth exhibits a minimum along the theta approximate to pi/4 direction of (a, c*) plane attributable to spin diffusion. Along the theta = pi/4 direction of (b, c*) plane the linewidth exhibits a maximum attributable to the two magnetically inequivalent sub-systems located in two adjacent mineral sheets. The simulations of EPR spectra obtained along the bisector of (b, c*) angle at room temperature and at T = 100 K show that exchange interaction between these two dissimilar sub-systems is nearly equal to zero.