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Landau theory is used to investigate the behavior of a metallic magnet driven toward a quantum critical point by the application of pressure. The observed dependence of the transition temperature with pressure is used to show that the coupling of the magnetic order to the lattice diverges as the quantum critical point is approached. This means that a first order transition will occur in magnets (both ferromagnets and antiferromagnets) because of the coupling to the lattice. The Landau equations are solved numerically without further approximations. There are other mechanisms that can cause a first order transition so the significance of this work is that it will enable us to determine the extent to which any particular first order transition is driven by coupling to the lattice or if other causes are responsible. [ABSTRACT FROM AUTHOR]

A dynamic model of the asymmetric Ising glass is presented: an Ising model with antiferromagnet bonds, -J, and ferromagnetic bonds, +J, with probabilities q and 1-q. The dynamics is introduced by changing the arrangement of the antiferromagnetic bonds after n Monte Carlo steps but keeping the same value of q and spin configuration. In the region where there is a second order transition between the ferromagnetic and paramagnetic states at Tc(q) for qq0 where there is a first order transition between the ferromagnetic and spin glass states where it shows no effects of motional narrowing. The implications of this are discussed. This model is devised to explain the properties of doped ZnO where the magnetization is reduced when the exchange interactions change with time. [ABSTRACT FROM AUTHOR]