Spin-frustrated V3 and Cu3 nanomagnets with Dzialoshinsky-Moriya exchange. 1. Inelastic neutron scattering and EPR in scalene, isosceles and equilateral trimers

Inelastic neutron scattering (INS) and EPR transitions are considered for the spin-frustrated V-3 and Cu-3 nanomagnets of the scalene, isosceles and equilateral triangle geometry with the Heisenberg and Dzialoshinsky-Moriya (DM) exchange interactions. Analytical expressions for the spin structure factors of the INS transitions show that the DM exchange and distortions determine the Q-dependence and redistribution of the intensities of the intra-doublet and doublet-doublet INS transitions in the 2(S = 1/2) states of the scalene and isosceles V-3 trimers. The anisotropy and the change of the intensities of the EPR transitions in these systems are also governed by the DM exchange and distortions. In the equilateral trimer with the DM exchange, the intensities of the INS and EPR transitions do not depend on the DM parameters. The theoretical results are compared with the INS and EPR spectra of the V-3 ring of Vis quantum molecular magnet, and with the EPR data of the [V-3] and {Cu-3} nanomagnets. It is shown that the Q-dependence of the INS intra-doublet transition and EPR spectra of V-3 ring of V-15 cannot be described by the scalene pure Heisenberg exchange model, as well as by the equilateral DM exchange model. The peculiarities of the INS and EPR spectra of the V-3 ring of V-15 and EPR spectra of the [V-3] and Cu-3 nanomagnets are described by the isosceles Heisenberg model with the DM exchange. For the {Cu-3} and [V-3] nanomagnets with strong DM exchange coupling, the theory predicts a large contribution of the DM exchange to the INS spectra. (C) 2009 Elsevier B.V. All rights reserved.