Temperature dynamics of magnetoactive compounds under terahertz irradiation: characterization by an EPR study

A possibility of fast rapid temperature changing for the studied compound makes it possible to study related phenomena, such as thermally induced trapping of metastable states in magnetoactive compounds and thermally activated catalytic and biological processes. The Electron Paramagnetic Resonance (EPR) spectroscopy station at the Novosibirsk Free Electron Laser (NovoFEL) allows one to study effects of powerful terahertz (THz) radiation on the spin state of paramagnetic systems. A change in the sample temperature as a result of radiation absorption is an inevitable consequence of such an exposure. However, the sample heating at the NovoFEL EPR station itself is of interest due to the record power of THz radiation and small sizes of the samples used. A combination of these two factors can provide a significantly high heating rate. The magnetoactive complex [Cu(hfac)₂L^Et] was chosen as a model system for studying the heating process, since the complex has a magnetostructural transition at ∼125 K with substantially different spin states above and below the transition temperature. The heating processes with the amplitudes above 60 K were studied, the heating and cooling rates of the sample in similar experiments were estimated, and prospects for using the method to study various thermally induced effects are discussed.