Abstract
Unambiguous evidence for the microscopic coexistence of ferromagnetism and superconductivity in UCoGe ($T_{\rm Curie} \sim 2.5$ K and $T_{\rm SC}$ $\sim$ 0.6 K) is reported from $^{59}$Co nuclear quadrupole resonance (NQR). The $^{59}$Co-NQR signal below 1 K indicates ferromagnetism throughout the sample volume, while nuclear spin-lattice relaxation rate $1/T_1$ in the ferromagnetic (FM) phase decreases below $T_{\rm SC}$ due to the opening of the superconducting(SC) gap. The SC state was found to be inhomogeneous, suggestive of a self-induced vortex state, potentially realizable in a FM superconductor. In addition, the $^{59}$Co-NQR spectrum around $T_{\rm Curie}$ show that the FM transition in UCoGe possesses a first-order character, which is consistent with the theoretical prediction that the low-temperature FM transition in itinerant magnets is generically of first-order.
Highlights
Journal of the Physical Society of JapanMicroscopic Coexistence of Ferromagnetism and Superconductivity in Single-Crystal UCoGe. Department of Physics, Graduate School of Science, Kyoto University, Kyoto 606-8502, Japan
The 59 Co-nuclear quadrupole resonance (NQR) signal below 1 K indicates ferromagnetism throughout the sample volume, while the nuclear spin-lattice relaxation rate 1=T1 in the ferromagnetic (FM) phase decreases below TSC due to the opening of the superconducting (SC) gap
We reported 59 Co-NQR studies in a polycrystalline UCoGe with TCurie 1⁄4 2:5 K and the SC onset onset temperature TSC
Summary
Microscopic Coexistence of Ferromagnetism and Superconductivity in Single-Crystal UCoGe. Department of Physics, Graduate School of Science, Kyoto University, Kyoto 606-8502, Japan. Unambiguous evidence for the microscopic coexistence of ferromagnetism and superconductivity in UCoGe (TCurie 2:5 K and TSC 0:6 K) is reported from 59 Co nuclear quadrupole resonance (NQR). To investigate intrinsic nature of UCoGe, 59 Co-NQR studies on a high-quality single crystal are highly desired Another interest in UCoGe is its FM transition. Belitz et al theoretically suggested that the sufficiently lowtemperature phase transition in itinerant ferromagnetism is generically of the first order.8) Experimental results supporting this have been reported in a few ferromagnets.9,10) In order to investigate the nature of the quantum FM transition occurring at T 1⁄4 0, UCoGe is one of the best ferromagnets, since TCurie of UCoGe is as low as 2.5 K.
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