Spin fluctuations and negative heat capacity (brief review)

The problem of negative heat capacity, discussed in a number of theoretical and experimental works dealing with weak itinerant magnets, is studied. A detailed analysis of the heat capacity of helicoidal itinerant magnet MnSi apparently demonstrates that the negative heat capacity in this case is a false effect because the interaction of the spin subsystem with other degrees of freedom is ignored in the analysis of the partial contributions to the heat capacity of the system. The negative heat capacity obtained by subtracting the electron and phonon components from the total heat capacity of the system is obviously an effective magnetic contribution, including the effects of spin–phonon coupling.