The 2D kagome system Pr3Ga5SiO14 has been previously identified as a spin-liquid candidate in zero field, displaying no magnetic long-ranged order down to at least 35 mK. Perturbations upon such ...systems, either under applied fields or applied pressure, should induce a spin freezing phase transition, but there are very few experimental realizations of this phenomena other than the well-studied 3D pyrochlore Tb2Ti2O7. In this Letter, we report the observation of a spin freezing phase transition in Pr3Ga5SiO14 through the application of chemical pressure--that is, through a systematic substitution on the Si site with larger ions and an elongation of the nearest-neighbor Pr-Pr distance in the kagome lattice. This results in a suppression of the T2 component of the heat capacity, and the reduction of the exchange constant eventually leads to dipolar-driven spin freezing.
Competition with magnetism is at the heart of high-temperature superconductivity, most intensely felt near a vortex core. To investigate vortex magnetism we have developed a spatially resolved probe ...based upon NMR spin-lattice-relaxation spectroscopy. With this approach we have found a spin-density wave associated with the vortex core in Bi(2)Sr(2)CaCu(2)O(8+y), similar to checkerboard patterns in the local density of electronic states reported from scanning tunneling microscope experiments. We have determined both the spin-modulation amplitude and decay length from the vortex core in fields up to H=30 T.
We report high-field magnetization, high-frequency electron spin resonance (ESR), and Se77 nuclear magnetic resonance (NMR) measurements on the linear spin tetramer system CuSeO3, consisting of ...strongly interacting Cu(1) dimers and weakly coupled Cu(2) spins. The magnetization exhibits anisotropic half-step magnetization plateaus at μ0H=45 T, depending on a crystallographic orientation. A temperature dependence of the ESR linewidth ΔHpp in a paramagnetic phase points towards the significance of anisotropic exchange interactions. Below TN=9–10 K long-range magnetic order is evidenced by the observation of a critical divergence of both ΔHpp(T) and the nuclear spin-lattice relaxation rate 1/T1. In addition, we identify a magnetic anomaly at T*=6.0(5) K below TN, which is caused by a spin reorientation. The nuclear spin-spin relaxation rate 1/T2 unveils the development of site-specific spin correlations. The intriguing magnetism of CuSeO3 is discussed in terms of the energy hierarchy of Cu(1) and Cu(2) spins in concert with additional intertetramer interactions.
Measurements of the O17 nuclear magnetic resonance (NMR) quadrupolar spectrum of apical oxygen in HgBa2CuO4+δ were performed over a range of magnetic fields from 6.4–30 T in the superconducting ...state. Oxygen-isotope-exchanged single crystals were investigated with doping corresponding to superconducting transition temperatures from 74 K underdoped, to 78 K overdoped. The apical oxygen site was chosen since its NMR spectrum has narrow quadrupolar satellites that are well separated from any other resonance. Nonvortex contributions to the spectra can be deconvolved in the time domain to determine the local magnetic field distribution from the vortices. Numerical analysis using Brandt's Ginzburg-Landau theory was used to find structural parameters of the vortex lattice, penetration depth, and coherence length as a function of magnetic field in the vortex solid phase. From this analysis we report a vortex structural transition near 15 T from an oblique lattice with an opening angle of 73∘ at low magnetic fields to a triangular lattice with 60∘ stabilized at high field. The temperature for onset of vortex dynamics has been identified from spin-spin relaxation. This is independent of the magnetic field at sufficiently high magnetic field similar to that reported for YBa2Cu3O7 and Bi2Sr2CaCu2O8+δ and is correlated with mass anisotropy of the material. This behavior is accounted for theoretically only in the limit of very high anisotropy.
The S = 1/2 antiferromagnetic Heisenberg chain exhibits a magnetic field driven quantum critical point. We study the low frequency spin dynamics in copper pyrazine dinitrate (CuPzN), a realization of ...this model system of quantum magnetism, by means of 13C‐NMR spectroscopy. Measurements of the nuclear spin–lattice relaxation rate $T_1^{ - 1}$ in the vicinity of the saturation field are compared with quantum Monte Carlo calculations of the dynamic structure factor. Both show a strong divergence of low energy excitations at temperatures in the quantum regime. The analysis of the anisotropic $T_1^{ - 1}$‐rates and frequency shifts allows one to disentangle the contributions from transverse and longitudinal spin fluctuations for a selective study and to determine the transfer of delocalized spin moments from copper to the neighboring nitrogen atoms.
We report the results of 63,65Cu-NMR measurements on single-layered copper-oxide Bi2Sr1.6La0.4CuO6+δ (Tc = 32 K) conducted under very high magnetic fields up to 45 T The high magnetic field ...suppresses superconductivity completely and the pseudogap ground state is revealed. The 63Cu-NMR Knight shift shows that there remains a finite density of states at the Fermi level in the zero-temperature limit, which indicates that the pseudogap ground state is a metallic state with a finite volume of Fermi surface.
Highly spin polarized (SP) and half-metallic ferromagnetic systems are of considerable current interest and of potential importance for spintronic applications. Recent work has demonstrated that ...Co1-xFexS2 is a highly polarized ferromagnet (FM) where the spin polarization can be tuned by alloy composition. Using 59Co FM-NMR as a probe, we have measured the low-temperature spin relaxation in this system in magnetic fields from 0 to 1.0 T for 0<or=x<or=0.3. The 59Co spin-lattice relaxation rates follow a linear T dependence. Analysis of the data, using expressions for a FM system, permits information to be obtained on the d-band density of states at the Fermi level. The results are compared with independent density of states values inferred from electronic specific heat measurements and band structure calculations. It is shown that FM-NMR can be an important method for investigating highly SP systems.
We present results for the pseudogap ground state and its doping evolution in single-layered copper-oxide Bi
2
Sr
2−
x
La
x
CuO
6+
δ
. We apply very high magnetic fields up to 44 T to remove the ...superconducting state and reveal the hidden low temperature (
T
) normal state. Through
63
Cu-NMR Knight shift and spin-lattice relaxation rate measurements, we find that there remains a finite density of states (DOS) at the Fermi level in the zero-
T
limit when the superconductivity is removed, which indicates that the pseudogap ground state is a metallic state with a finite volume of Fermi surface. The residual DOS in the pseudogap ground state decreases with decreasing doping (increasing
x
), but remains quite large even at the vicinity of the magnetically ordered phase of
x
≥ 0.8. The result indicates that the superconductivity emerges from the remaining Fermi surface and coexists with the pseudogap.
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