Abstract

We present a theory of the quantum Griffiths phases associated with the ferromagnetic quantum phase transition in disordered metals. For Ising spin symmetry, we study the dynamics of a single rare region within the variational instanton approach. For Heisenberg symmetry, the dynamics of the rare region is studied using a renormalization group approach. In both cases, the rare region dynamics is even slower than in the usual quantum Griffiths case because the order parameter conservation of an itinerant ferromagnet hampers the relaxation of large magnetic clusters. The resulting quantum Griffiths singularities in ferromagnetic metals are stronger than power laws. For example, the low-energy density of states ρ(ε) takes the asymptotic form exp[ { -λlog (ε 0 /ε )}3 /5]/ε with λ being nonuniversal. We contrast these results with the antiferromagnetic case in which the systems show power-law quantum Griffiths singularities in the vicinity of the quantum critical point. We also compare our result with existing experimental data of ferromagnetic alloy Ni xV 1-x.

Department(s)

Physics

International Standard Serial Number (ISSN)

1098-0121

Document Type

Article - Journal

Document Version

Final Version

File Type

text

Language(s)

English

Rights

© 2012 American Physical Society (APS), All rights reserved.

Included in

Physics Commons

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