Thermal properties of ferrimagnetic systems

Abstract

The heat capacity of some ferrimagnets has additional structures like a shoulder in the Schottky-like peak, or emergence of a second peak when an external magnetic field is applied. It is shown here that as long as spin wave-spin wave interactions are ignored in a ferrimagnet, the ferromagnetic and antiferromagnetic elementary excitation spectra give rise to two independent heat capacity peaks, one enveloped by the other, which add up to give the peak for the total system. Taking this into account helps understand the additional structures in the peaks. Moreover, the classification of ferrimagnets into predominantly antiferromagnetic, ferromagnetic, or a mixture of the two is shown to be validated by studying them under additional influences like dimerization and frustration. Because these two are shown to influence the ferromagnetic and antiferromagnetic dispersion relations - and hence the quantities like heat capacity and magnetic susceptibility - by different amounts, the characterisation of ferrimagnetic systems ($1,1/2$), ($3/2,1$) and ($3/2,1/2$) is brought out more clearly. Both these influences enhance antiferromagnetic character.