High field high frequency EPR techniques and their application to single molecule magnets

We present details of a new high-field/high-frequency EPR technique, and its application to measurements of singlemolecule magnets (SMMs). By using a quasi-optical set-up and microwave sources covering a continuous frequency range from 170 to 600 GHz; in conjunction with a millimetre-wave vector network analyser, we are able to measure EPR to high magnetic fields. For example, a g 1⁄4 2 system will exhibit EPR at about 14 T at a frequency of 400 GHz: We illustrate the technique by presenting details of recent high-frequency experiments on several SMMs which are variations of the well-known SMM Mn12-Ac: This material has a spin ground state of S 1⁄4 10 and large uniaxial anisotropy, hence frequencies above 300 GHz are required in order to observe EPR from the ground state. r 2004 Elsevier B.V. All rights reserved. PACS: 76.30. v; 75.50.Xx; 75.45.þj