Criticality in inhomogeneous magnetic systems: Application to quantum ferromagnets

D. Belitz, T. R. Kirkpatrick, Ronojoy Saha

Published 2007-05-01, updated 2007-08-24Version 2

We consider a $\phi^4$-theory with a position-dependent distance from the critical point. One realization of this model is a classical ferromagnet subject to non-uniform mechanical stress. We find a sharp phase transition where the envelope of the local magnetization vanishes uniformly. The first-order transition in a quantum ferromagnet also remains sharp. The universal mechanism leading to a tricritical point in an itinerant quantum ferromagnet is suppressed, and in principle one can recover a quantum critical point with mean-field exponents. Observable consequences of these results are discussed.