Giant magnetic Grüneisen parameters in nearly ferromagnetic and heavy-fermion systems

The size of the volume magnetostriction in paramagnetic systems determines a magnetic Grüneisen parameter in analogy to the usual thermal Grüneisen parameter. Both nearly ferromagnetic and heavy-fermion systems show magnetic Grüneisen parameters up to 2 orders of magnitude larger than for normal metals. The thermal Grüneisen parameter in nearly magnetic systems, however, remains only modestly enhanced, in strong contrast to heavy-fermion and mixed-valence compounds in which the two Grüneisen parameters appear to be of comparable size. The origin of the discrepancy can be understood in terms of the Fermi-liquid parameter $F_0^a$.