Quantum phase transitions in NbFe 2 and Ca 3 Ru 2 O 7

Abstract We examine the low temperature states of two transition metal compounds: (i) NbFe 2 is poised on the threshold of ferromagnetism and can be pushed into a spin‐aligned state at low temperature by modifying the composition slightly. Stoichiometric NbFe 2 has been reported as a rare example of...

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Published in:physica status solidi (b) 2010-03, Vol.247 (3), p.544-548
Main Authors: Duncan, W. J., Welzel, O. P., Moroni‐Klementowicz, D., Albrecht, C., Niklowitz, P. G., Grüner, D., Brando, M., Neubauer, A., Pfleiderer, C., Kikugawa, N., Mackenzie, A. P., Grosche, F. M.
Format: Article
Language:English
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Summary:Abstract We examine the low temperature states of two transition metal compounds: (i) NbFe 2 is poised on the threshold of ferromagnetism and can be pushed into a spin‐aligned state at low temperature by modifying the composition slightly. Stoichiometric NbFe 2 has been reported as a rare example of low‐temperature spin density wave order in a d‐metal system. We have used pressure, field and composition tuning to examine the phase diagram of NbFe 2 . Near the quantum critical point, we find distinct non‐Fermi liquid forms of the resistivity and heat capacity, whereas we observe strong, hysteretic magnetoresistance effects deep in the ordered phase. (ii) Ca 3 Ru 2 O 7 undergoes first a magnetic transition ( T N  = 56 K) and then a structural transition ( T S  = 48 K) on cooling. Most of the Fermi surface is gapped out at low temperature, leading to a very low carrier density and small Fermi surface pockets. Pressure suppresses both T N and T S and, for p  > 3.5 GPa, induces a third low temperature state, which is robust up to at least 7.5 GPa.
ISSN:0370-1972
1521-3951
DOI:10.1002/pssb.200983079