Magnetoelectric Coupling\nin a Mn<sub>4</sub>Na–Organic\nComplex under Pulsed Magnetic Fields up to 73 T

Research on the magnetoelectric (ME) effect (or spin-electric\ncoupling)\nin molecule-based magnetic materials is a relatively nascent but promising\ntopic. Molecule-based magnetic materials have diverse magnetic functionalities\nthat can be coupled to electrical properties. Here we investigate\na realization of ME coupling that is fundamental but not heavily studiedthe\ncoupling of magnetic spin level crossings to changes in electric polarization.\nA mixed-valence Mn<sub>4</sub>Na complex with a total ground-state\nspin <i>S</i> = 5/2 under zero magnetic field and <i>S</i> = 17/2 under high magnetic field undergoes a cascade of\nground-state level crossings of the <i>S</i><sub><i>z</i></sub> states with increasing magnetic field. Magnetization\nand electrical polarization measurements under pulsed magnetic fields\nup to 73 T show that each spin level crossing is accompanied by a\nsignificant change in electric polarization that is an even function\nof the applied magnetic field. A molecular Hamiltonian describing\nantiferromagnetic exchange in a distorted tetrahedron of three Mn<sup>III</sup> and one Mn<sup>II</sup> ions matches the data well. We\nconclude that the ME coupling is caused by magnetostriction within\nthe polar molecule as it distorts to lower its magnetic exchange energy.