Nonlinearity and harmonics of the magnetic susceptibility of a Co-=SUP=-2+-=/SUP=- single-ion magnet in the paramagnetic region above the magnetic ordering temperature

Abstract

In single-ion complexes based on Co2+ ions, the second and third harmonics of the magnetic susceptibility were found at temperatures of 2-4 K, which exceed the Neel temperature. The maxima of the second and third harmonics of the magnetic susceptibility are observed at a frequency of ~1 Hz, at which the maximum of the first harmonic is observed in a field of 3.2 kOe. An analysis of the dependences of the second and third harmonics of the magnetic susceptibility on the field and temperature showed that the nonlinearity arises as a result of the formation of a spin glass state at temperatures slightly higher than the Neel temperature. In this state, there is no long-range spin order, but there are spin clusters in the spin glass state. The spin-glass state in a compound with a Co2+ ion with a high magnetic anisotropy is unusual in that the exchange interaction is much smaller than the single-ion anisotropy energy. Keywords: molecular magnets, nonlinear magnetic susceptibility, nanostructures, spin dynamics, spin glass.