Superconductivity and Quantum Phase Transitions in Weak Itinerant Ferromagnets
It is argued that the phase transition in low Tc clean itinerant ferromagnets is generically of first order, due to correlation effects that lead to a nonanalytic term in the free energy. A tricritical point separates the line of first order transitions from Heisenberg critical behavior at higher temperatures. Sufficiently strong quenched disorder suppresses the first order transition via the appearance of a critical endpoint. A semi-quantitative discussion is given in terms of recent experiments on MnSi and UGe2. It is then shown that the critical temperature for spin-triplet, p-wave superconductivity mediated by spin fluctuations is generically much higher in a Heisenberg ferromagnetic phase than in a paramagnetic one, due to the coupling of magnons to the longitudinal magnetic susceptibility. This qualitatively explains the phase diagram recently observed in UGe2 and ZrZn2.
T. R. Kirkpatrick et al., "Superconductivity and Quantum Phase Transitions in Weak Itinerant Ferromagnets," International Journal of Modern Physics B, vol. 17, no. 28, pp. 5081-5091, World Scientific Publishing, Nov 2003.
The definitive version is available at http://dx.doi.org/10.1142/S0217979203020211
Keywords and Phrases
ferromagnetic material; germanium; manganese; silicon dioxide; uranium; energy; magnetism; mathematical analysis; phase transition; temperature
International Standard Serial Number (ISSN)
Article - Journal
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