Anisotropic Magnetic Fluctuations in the Ferromagnetic Superconductor UCoGe Studied by Direction-Dependent<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mmultiscripts><mml:mi>Co</mml:mi><mml:mprescripts /><mml:none /><mml:mn>59</mml:mn></mml:mmultiscripts></mml:math>NMR Measurements

Ihara, Yukitoshi; Hattori, T.; Ishida, K.; Nakai, Yusuke; Osaki, E.; Deguchi, K.; Sato, Noriaki; Satoh, Ichiro

doi:10.1103/physrevlett.105.206403

Cited by 60 publications

(68 citation statements)

References 20 publications

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“…The presence of the 3-D FM fluctuations is also consistent with the resistivity data [ρ(T ) ∝ T 5/3 ] measured in zero field 18 . We comment on that the similar Ising magnetic fluctuations were observed in a ferromagnetic superconductor UCoGe 16,17 .…”

Section: Resultsmentioning

confidence: 80%

Universality and critical behavior at the critical endpoint in the itinerant-electron metamagnet UCoAl

et al. 2012

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We performed nuclear-magnetic-resonance (NMR) measurements on itinerant-electron metamagnet UCoAl in order to investigate the critical behavior of the magnetism near a metamagnetic (MM) critical endpoint (CEP). We derived c-axis magnetization Mc and its fluctuation Sc from the measurements of Knight shift and nuclear spin-lattice relaxation rate 1/T1 as a function of the c-axis external field (Hc) and temperature (T ). We developed contour plots of Mc and Sc on the Hc -T phase diagram, and observed the strong divergence of Sc at the CEP. The critical exponents of Mc and Sc near the CEP are estimated, and found to be close to the universal properties of a threedimensional (3-D) Ising model. We indicate that the critical phenomena at the itinerant-electron MM CEP in UCoAl have a common feature as a gas-liquid transition.

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Section: Resultsmentioning

confidence: 80%

Universality and critical behavior at the critical endpoint in the itinerant-electron metamagnet UCoAl

et al. 2012

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“…18,19) The FM transition temperature T Curie of the singlecrystal sample was evaluated to be 2.55±0.1 K from the Arrot plots shown in the inset of anisotropic behavior was observed with the easy axis along the c axis. The magnitude of µ s was determined to be 0.07 µ B /Co by extrapolating at T = 0.…”

Section: Methodsmentioning

confidence: 99%

“…. 19) Since the temperature where the second component emerges coincides with T SC for both single-crystal and polycrystalline samples, the two-relaxation rate behavior would be intrinsic. At present, although we cannot exclude the possibility that non-SC component is an impurity effect, an interesting possibility is a self-induced vortex (SIV) state.…”

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confidence: 99%

⁵⁹Co-NMR/Nuclear-Quadrupole-Resonance (NQR) Studies on Ferromagnetic Superconductor UCoGe

et al. 2011

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We have performed NMR and nuclear-quadrupole-resonance (NQR) on U-based ferromagnetic superconductor UCoGe and a reference metallic compound YCoGe without 5 f electrons, in order to investigate the normal and superconducting-state properties. From 59 Co-NQR measurements, we give clear evidence that ferromagnetism and superconductivity coexist microscopically, both of which are ascribed to the U 5 f -electrons. In addition, direction-dependent Knight shift and nuclear spin-lattice relaxation rate measurements provide microscopic evidence that both static and dynamic susceptibilities are ferromagnetic with strong Ising anisotropy. We point out that superconductivity induced by such magnetic fluctuations prefers spin-triplet pairing state

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“…The magnetization has Ising-like anisotropy with the c axis as a magnetic easy axis, and direction-dependent nuclear-spin lattice relaxation rate (1/T 1 ) measurements on a single crystalline sample have revealed the magnetic fluctuations in UCoGe to be Ising-type FM ones along the c axis (longitudinal FM spin fluctuations) [10]. Here, we report from precise angle-resolved 1/T 1 and H c2 measurements how the longitudinal FM spin fluctuations are sensitively affected by the fields along the c axis (H c ), and are linked with the superconductivity.…”

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“…When a nucleus with a spin larger than unity sits at a position where the electric field gradient (EFG) is finite, the nuclear quadrupole interaction splits the NMR spectrum. Since the EFG parameters for Co site have determined from the previous 59 Co NQR / NMR experiments [7,10] ( the quadrupole interaction of 2.85 MHz ∼ 0.28 T and the direction of maximum EFG principal axis of 10 • from a axis in ac plane ), we can check θ from the quadrupole-split NMR spectrum. The angle-dependent NMR spectra are well simulated by these EFG parameters [11].…”

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Superconductivity Induced by Longitudinal Ferromagnetic Fluctuations in UCoGe

et al. 2012

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From detailed angle-resolved NMR and Meissner measurements on a ferromagnetic (FM) superconductor UCoGe (TCurie ∼ 2.5 K and TSC ∼ 0.6 K), we show that superconductivity in UCoGe is tightly coupled with longitudinal FM spin fluctuations along the c axis. We found that magnetic fields along the c axis (H c) strongly suppress the FM fluctuations and that the superconductivity is observed in the limited magnetic-field region where the longitudinal FM spin fluctuations are active. These results combined with model calculations strongly suggest that the longitudinal FM spin fluctuations tuned by H c induce the unique spin-triplet superconductivity in UCoGe. This is the first clear example that FM fluctuations are intimately related with superconductivity.PACS numbers: 71.27.+a 74.25.nj, 75.30.Gw The discovery of superconductivity in ferromagnetic (FM) UGe 2 opened up a new paradigm of superconductivity [1,2], since most unconventional superconductivity has been discovered in the vicinity of an antiferromagnetic (AFM) phase [3]. From the theoretical point of view, in an itinerant FM superconductor with the presence of a large energy splitting between the majority and minority spin Fermi surfaces, exotic spintriplet superconductivity is anticipated, in which pairing is between parallel spins within each spin Fermi surface. In addition, it has been argued that critical FM fluctuations near a quantum phase transition could mediate spin-triplet superconductivity [4]. However, there have been no experimental results indicating a relationship between FM fluctuations and superconductivity.Among the FM superconductors discovered so far, UCoGe is one of the most readily explored experimentally, because of its high superconducting (SC) transition temperature (T SC ) and low Curie temperature (T Curie ) at ambient pressure [5]. Microscopic measurements have shown that superconductivity occurs within the FM region, resulting in microscopic coexistence of ferromagnetism and superconductivity [6,7]. Studies of the SC upper critical field (H c2 ) and its angle dependence along each crystalline axis have reported remarkable enigmatic behavior [8,9]: superconductivity survives far beyond the Pauli-limiting field along the a and b axes, whereas H c2 for fields along the c direction (H c c2 ) is as small as 0.5 T. Colossal H c2 for fields along the a and b axes seems to suggest spin triplet pairing. In addition, a steep angle dependence of H c2 was reported when the field was tilted slightly from the a axis toward the c axis [9]. The observed characteristic H c2 behavior is one of mysterious features of SC UCoGe and its origin can be related to the mechanism of the superconductivity.Unlike the three dimensional crystal structure, magnetic properties are strongly anisotropic [8]. The magnetization has Ising-like anisotropy with the c axis as a magnetic easy axis, and direction-dependent nuclear-spin lattice relaxation rate (1/T 1 ) measurements on a single crystalline sample have revealed the magnetic fluctuations in UCoGe to be Ising-...

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Anisotropic Magnetic Fluctuations in the Ferromagnetic Superconductor UCoGe Studied by Direction-DependentCo59NMR Measurements

Cited by 60 publications

References 20 publications

Universality and critical behavior at the critical endpoint in the itinerant-electron metamagnet UCoAl

Universality and critical behavior at the critical endpoint in the itinerant-electron metamagnet UCoAl

⁵⁹Co-NMR/Nuclear-Quadrupole-Resonance (NQR) Studies on Ferromagnetic Superconductor UCoGe

Superconductivity Induced by Longitudinal Ferromagnetic Fluctuations in UCoGe

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Anisotropic Magnetic Fluctuations in the Ferromagnetic Superconductor UCoGe Studied by Direction-DependentCo59NMR Measurements

Cited by 60 publications

References 20 publications

Universality and critical behavior at the critical endpoint in the itinerant-electron metamagnet UCoAl

Universality and critical behavior at the critical endpoint in the itinerant-electron metamagnet UCoAl

59Co-NMR/Nuclear-Quadrupole-Resonance (NQR) Studies on Ferromagnetic Superconductor UCoGe

Superconductivity Induced by Longitudinal Ferromagnetic Fluctuations in UCoGe

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⁵⁹Co-NMR/Nuclear-Quadrupole-Resonance (NQR) Studies on Ferromagnetic Superconductor UCoGe