Quantum criticality in itinerant metamagnets

Critical thermodynamics close to a metamagnetic quantum critical endpoint (QCEP) in a metal is discussed within the framework of spin-fluctuation theory. We analyze the effective potential for the Ising order parameter that is renormalized by spin-fluctuations and acquires a characteristic temperature dependence. The resulting magnetic field, H, and temperature, T, dependence of the magnetization, specific heat, thermal expansion, magnetostriction, susceptibility and the Gr\"uneisen parameter are determined, and the crossover lines in the (H,T) phase diagram are specified. We point out that the metamagnetic QCEP is intrinsically unstable with respect to a magnetoelastic coupling.