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Phase separation and suppression of critical dynamics at quantum transitions of itinerant magnets: MnSi and (Sr$_{1-x}$Ca$_{x}$)RuO$_{3}$

Y. J. Uemura·T. Goko·I. M. Gat-Malureanu·J. P. Carlo·P. L. Russo·A. T. Savici·A. Aczel·G. J. MacDougall·J. A. Rdoriguez·G. M. Luke·S. R. Dunsiger·A. McCollam·J. Arai·Ch. Pfleiderer·P. Boeni·K. Yoshimura·E. Baggio-Saitovitch·M. B. Fontes·J. Larrea J.·Y. V. Sushko·J. Sereni
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Abstract

Quantum phase transitions (QPTs) have been studied extensively in correlated electron systems. Characterization of magnetism at QPTs has, however, been limited by the volume-integrated feature of neutron and magnetization measurements and by pressure uncertainties in NMR studies using powderized specimens. Overcoming these limitations, we performed muon spin relaxation ($μ$SR) measurements which have a unique sensitivity to volume fractions of magnetically ordered and paramagnetic regions, and studied QPTs from itinerant heli/ferro magnet to paramagnet in MnSi (single-crystal; varying pressure) and (Sr$_{1-x}$Ca$_{x}$)RuO$_{3}$ (ceramic specimens; varying $x$). Our results provide the first clear evidence that both cases are associated with spontaneous phase separation and suppression of dynamic critical behavior, revealed a slow but dynamic character of the ``partial order'' diffuse spin correlations in MnSi above the critical pressure, and, combined with other known results in heavy-fermion and cuprate systems, suggest a possibility that a majority of QPTs involve first-order transitions and/or phase separation.

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Y. J. Uemura, T. Goko, I. M. Gat-Malureanu, J. P. Carlo, P. L. Russo, A. T. Savici, A. Aczel, G. J. MacDougall, J. A. Rdoriguez, G. M. Luke, S. R. Dunsiger, A. McCollam, J. Arai, Ch. Pfleiderer, P. Boeni, K. Yoshimura, E. Baggio-Saitovitch, M. B. Fontes, J. Larrea J., Y. V. Sushko, J. Sereni. 2006-12-17. Phase separation and suppression of critical dynamics at quantum transitions of itinerant magnets: MnSi and (Sr$_{1-x}$Ca$_{x}$)RuO$_{3}$. https://doi.org/10.1038/nphys488

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