The magnetic phases of the ideal spin-1/2 triangular-lattice antiferromagnet Ba3CoSb2O9 are identified and studied using 135,137 Ba nuclear magnetic resonance (NMR) spectroscopy in magnetic fields ranging to 30T, oriented parallel and near perpendicular to the crystallographic ab-plane. For both directions, the saturation field is approximately 33T. Notably, the NMR spectra provide microscopic evidence for the stabilization of an up-up-down spin configuration for in-plane fields, giving rise to an one-third magnetization plateau (Msat/3), as well as for a higher field phase transition near to ∼ (3/5)Msat for both field orientations. Phase transitions are signaled by the evolution of the NMR spectra, and in some cases through spin-lattice relaxation measurements. The results are compared with expectations obtained from a semi-classical energy density modeling, in which quantum effects are incorporated by effective interactions extracted from the spin-wave analysis of the two-dimensional model. The interlayer coupling also plays a significant role in the outcome. Good agreement between the model and the experimental results is achieved, except for the case of fields approaching the saturation value applied along the c-axis.

We present nuclear magnetic resonance (NMR) measurements on the three distinct In sites of CeCoIn5 with magnetic field applied in the [100] direction. We identify the microscopic nature of the long range magnetic order (LRO) stabilized at low temperatures in fields above 10.2 T while still in the superconducting (SC) state. We infer that the ordered moment is oriented along theĉ-axis and map its field evolution. The study of the field dependence of the NMR shift for the different In sites indicates that the LRO likely coexists with a modulated SC phase, possibly that predicted by Fulde, Ferrell, Larkin, and Ovchinnikov. Furthermore, we discern a field region dominated by strong spin fluctuations where static LRO is absent and propose a revised phase diagram.The detrimental effect of an applied magnetic field on a superconductor has nourished the intuitive presumption of a de facto competition between magnetic and superconducting (SC) orders. However, it is now wellestablished, both theoretically and experimentally, that not only can these orders coexist, but in some cases, they may even be essential for each other's stability [1]. Manifestations of coexistence span a rather wide range of materials including several cuprates, ferropnictides, and heavy fermion systems of which CeCoIn 5 is one of the most intriguing examples [2]. In the SC state of this compound application of a magnetic field (H 0 ) induces a long range magnetic order (LRO), restricted to a narrow lowtemperature (T ) region of the phase diagram below H c2 [3,4]. What is more, this particular region of the phase diagram was initially identified as the first realization of the long-sought Fulde, Ferrell, Larkin, and Ovchinnikov (FFLO) state, a superconducting state with a non-zero pair momentum and a spatially modulated order parameter [5,6]. However, important questions regarding the true nature of the low-T high-H 0 SC phase, the details of the magnetic order and its field dependence, and the potential driving mechanisms of their coexistence remain unanswered [7]. Thus, CeCoIn 5 provides a strikingly rich ground to study the complex interplay between exotic SC and magnetism. Experimentally, nuclear magnetic resonance (NMR), as a microscopic probe sensitive to both magnetic and SC degrees of freedom, provides a powerful tool for the investigation of these puzzles.In this letter, detailed low temperature NMR measurements on the three distinct In sites in CeCoIn 5 for H 0 || [100] are presented. We establish that at T ≈ 70 mK a phase with static magnetic LRO is stabilized for fields above ≈ 10.2 T in the SC state. We deduce that the LRO is an incommensurate spin density wave (IC-SDW) with moments oriented along theĉ-axis, independent of the in-plane H 0 orientation. Further, the detailed field evolution of the moment is mapped. The study of the field dependence of the NMR shift implies that this IC-SDW coexists with a novel SC state, characterized by an enhanced spin susceptibility [8]. Finally, we identify a new region in the H 0 -T phase diagram, l...

Quasi-two dimensional superconductors with sufficiently weak interlayer coupling allow magnetic flux to penetrate in the form of Josephson vortices for in-plane applied magnetic fields. A consequence is the dominance of the Zeeman interaction over orbital effects. In the clean limit, the normal state is favored over superconductivity for fields greater than the paramagnetic limiting field, unless an intermediate, inhomogeneous state is stabilized. Presented here are nuclear magnetic resonance (NMR) studies of the inhomogeneous (FFLO) state for β -(ET)2SF5CH2CF2SO3. The uniform superconductivity-FFLO transition is identified at an applied field value of 9.3(0.1) T at low temperature (T = 130 mK), and evidence for a possible second transition between inhomogeneous states at ∼ 11 T is presented. The spin polarization distribution inferred from the NMR absorption spectrum compares favorably to a single-Q modulation of the superconducting order parameter.

In principle, the spin-½ plutonium-239 ((239)Pu) nucleus should be active in nuclear magnetic resonance spectroscopy. However, its signal has eluded detection for the past 50 years. Here, we report observation of a (239)Pu resonance from a solid sample of plutonium dioxide (PuO(2)) subjected to a wide scan of external magnetic field values (3 to 8 tesla) at a temperature of 4 kelvin. By mapping the external field dependence of the measured resonance frequency, we determined the nuclear gyromagnetic ratio (239)γ(n)(PuO(2))/2π to be 2.856 ± 0.001 megahertz per tesla (MHz/T). Assuming a free-ion value for the Pu(4+) hyperfine coupling constant, we estimated a bare (239)γ(n)/2π value of ~2.29 MHz/T, corresponding to a nuclear magnetic moment of μ(n) ≈ 0.15μ(N) (where μ(N) is the nuclear magneton).