Many-spin effects in inelastic neutron scattering and electron paramagnetic resonance of molecular nanomagnets

Abstract

Many molecular magnetic clusters, such as single-molecule magnets, are characterized by spin ground states with defined total spin S exhibiting zero-field-splittings. In this work, the spectroscopic intensities of the transitions within the ground-state multiplet are analyzed. In particular, the effects of a mixing with higher-lying spin multiplets, which is produced by anisotropic interactions and is neglected in the standard single-spin description, are investigated systematically for the two experimental techniques of inelastic neutron scattering (INS) and electron paramagnetic resonance (EPR), with emphasis on the former technique. The spectroscopic transition intensities are calculated analytically by constructing corresponding effective spin operators perturbationally up to second order and consequently using irreducible tensor operator techniques. Three main effects of spin mixing are observed. Firstly, a pronounced dependence of the INS intensities on the momentum transfer Q, with a typical oscillatory behavior, emerges in first order, signaling the many-spin nature of the wave functions in exchange-coupled clusters. Secondly, as compared to the results of a first-order calculation, the intensities of the transitions within the spin multiplet are affected differently by spin mixing. This allows one, thirdly, to differentiate the higher-order contributions to the cluster magnetic anisotropy which come from the single-ion ligand-field terms and spin mixing, respectively. The analytical results are illustrated by means of the three examples of an antiferromagnetic heteronuclear dimer, the Mn-[3 x 3] grid molecule, and the single-molecule magnet Mn12.

18 pages, 3 figures, REVTEX4, to appear in PRB

References in corpus (13)

• Low-Temperature Quantum Relaxation in a System of Magnetic Nanomolecules
• Low energy magnetic excitations of the Mn_{12}-acetate spin cluster observed by neutron scattering
• Elementary excitations in the cyclic molecular nanomagnet Cr8
• Quantum Coherence between High Spin Superposition States of Single Molecule Magnet Ni${}_4$
• S-mixing and quantum tunneling of the magnetization in molecular nanomagnets
• Field dependent anisotropy change in a supramolecular Mn(II)-[3x3] grid
• Exchange Interactions and High-Energy Spin States in Mn_12-acetate
• Q-dependence of the inelastic neutron scattering cross section for molecular spin clusters with high molecular symmetry
• Mesoscopic quantum coherence in antiferromagnetic molecular clusters
• Quantum-magneto oscillations in a supramolecular Mn(II)-[3 x 3] grid
• Transverse Magnetic Anisotropy in Mn12-acetate: Direct Determination by Inelastic Neutron Scattering
• Pressure Dependence of the Magnetic Anisotropy in the "Single-Molecule Magnet" [Mn4O3Br(OAc)3(dbm)3]
• Macroscopic evidence of quantum coherent oscillations of the total spin in the Mn-[3x3] molecular nanomagnet

Cited by in corpus (14)

• Magnetic Cluster Excitations
• Discrete antiferromagnetic spin-wave excitations in the giant ferric wheel Fe18
• Single-ion and exchange anisotropy effects and multiferroic behavior in high-symmetry tetramer single molecule magnets
• Theory of high-symmetry tetramer single molecule magnets
• Quantized antiferromagnetic spin waves in the molecular Heisenberg ring CsFe${}_8$
• Direct observation of mixing of spin-multiplets in an antiferromagnetic molecular nanomagnet by electron paramagnetic resonance
• Quantum dynamics of the Neel vector in the antiferromagnetic molecular wheel CsFe8
• Inelastic neutron scattering and frequency domain magnetic resonance studies of S=4 and S=12 Mn${}_6$ single-molecule magnets
• Exchange-coupling constants, spin density map, and Q dependence of the inelastic neutron scattering intensity in single-molecule magnets
• Spin excitation spectra of the two dimensional $S=1/2$ Heisenberg model with a checkerboard structure
• Spin anisotropy effects in dimer single molecule magnets
• Inelastic neutron scattering study and Hubbard model description of the antiferromagnetic tetrahedral molecule Ni4Mo12
• Magic angle effects in a trigonal Mn(III)3 cluster: deconstruction of a single-molecule magnet
• Projective spin adaptation for the exact diagonalization of isotropic spin clusters