EPR of layered magnetic metal—amino acid salts. I. Cu(L-PHE)2

Abstract

EPR measurements in single crystals of Cu(L-PHE)2, the copper derivative of the amino acid L-phenylalanine, were performed at 300 K and 9.7 GHz. The gyromagnetic factor, g, and the linewidth of the single EPR line were measured in three perpendicular planes of the sample. The gyromagnetic tensor was obtained, and its principal values are g1 = 2.211, g2 = 2.134, and g3 = 2.075. The single resonance is explained by the collapse of the resonances of the two magnetically non-equivalent copper sites due to the exchange interaction. The molecular g-factor of isolated copper ions is obtained from a model assuming axial symmetry. The results are g| = 2.266 and g⊥ = 2.075, indicating a d(x2 - y2) ground orbital. The orientations of the molecules in the crystal obtained by this model are in agreement with the crystallographic values. The linewidth data support a model which assumes exchange narrowing of the magnetic dipolar interaction in a two-dimensional magnetic structure, an incomplete collapse of the hyperfine structure, and contributions arising from non-isotropic exchange. A mean value ¦J¦=0.19 K is calculated for the isotropic exchange interactions between one copper and its six copper neighbors in Cu(L-PHE)2. Also, a lower limit ¦J′¦ > 0.02 K for the exchange coupling J′ between non-equivalent copper neighbors is obtained.