Influence of Polymorphism on the Magnetic Properties of Single-Molecule Magnets According to the Data of EPR Spectroscop
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uence of Polymorphism on the Magnetic Properties of Single-Molecule Magnets According to the Data of EPR Spectroscopy in the Terahertz Range V. V. Novikova, *, A. A. Pavlova, J. Nehrkornb, and Yu. V. Nelyubinaa aNesmeyanov
Institute of Organoelement Compounds, Russian Academy of Sciences, Moscow, 119991 Russia Max Planck Institute for Chemical Energy Conversion, Mülheim an der Ruhr, Germany *е-mail: [email protected]
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Received May 9, 2020; revised June 8, 2020; accepted June 10, 2020
Abstract—Two earlier described polymorphous modifications of the cobalt(II) (pseudo)clathrochelate are studied by EPR spectroscopy in the terahertz range, where the complex exhibits the properties of a singlemolecule magnet (including the record-breaking barrier for magnetization reversal at the moment). Different values of the magnetization reversal barrier found previously for the corresponding crystalline phases by the results of magnetometric measurements in an alternating magnetic field are observed in the EPR spectra in the terahertz range. A combined analysis of these two methods allows one to more precisely estimate the magnetization reversal barrier for two polymorphous modifications and also the contribution of different magnetic relaxation mechanisms to the spin dynamics. This unambiguously confirms that slight changes in the crystalline environment of the molecule of even such structurally rigid metal complexes as cobalt(II) (pseudo)clathrochelates can result in high differences in the magnetization reversal barrier, which is the key characteristic of single-molecule magnets. Keywords: clathrochelates, cobalt complexes, single-molecule magnets, magnetometry in alternating magnetic field, EPR spectroscopy in terahertz range DOI: 10.1134/S1070328420110056
INTRODUCTION The studies of single-molecule magnets (SMM), viz., chemical compounds capable of manifesting the properties of macroscopic magnets already at the level of an individual molecule, become popular in the world scientific society in the recent time [1]. This makes it possible to produce from them devices of superdense information storage [2] and molecular spintronics [3] and to use them as quantum bits (qubits) for quantum computers [4]. One of the main characteristics of SMM is slow magnetic relaxation, which is primarily caused by their very high magnetic anisotropy [5]. In the case of complexes of the first row transition metals, this phenomenon is related to the splitting energy in the zero field (D) of the metal ion [6], which results in the appearance of the barrier (often named the Orbach barrier) for the thermally activated process of magnetization reversal [7]. However, the properties of SMM are determined not only by the magnetization reversal barrier (MRB) but also by other magnetic relaxation mechanisms, whose contribution to the spin dynamics of the system depends on the nature and structure of the compound under study, its phase state, intermolecular interactions, and even temperature and external magnetic field [8].
We have recently shown [9]
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