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Abstract:
An overview of quantum phase transitions (QPTs) in metallic
ferromagnets, discussing both experimental and theoretical aspects, is
given. These QPTs can be classified with respect to the presence and
strength of quenched disorder: Clean systems generically show a
discontinuous, or first-order, QPT from a ferromagnetic to a
paramagnetic state as a function of some control parameter, as predicted
by theory. Disordered systems are much more complicated, depending on
the disorder strength and the distance from the QPT. In many disordered
materials the QPT is continuous, or second order, and Griffiths-phase
effects coexist with QPT singularities near the transition. In other
systems the transition from the ferromagnetic state at low temperatures
is to a different type of long-range order, such as an antiferromagnetic
or a spin-density-wave state. In still other materials a transition to a
state with glasslike spin dynamics is suspected. The review provides a
comprehensive discussion of the current understanding of these various
transitions and of the relation between experiment and theory.
