395 research outputs found
Review of NMR studies of nanoscale molecular magnets composed of geometrically frustrated antiferromagnetic triangles
We present a comprehensive review of nuclear magnetic resonance (NMR) studies
performed on three nanoscale molecular magnets with different configurations of
geometrically frustrated antiferromagnetic (AFM) triangles, new spin
frustration systems with different novel structures: (1) the isolated single
AFM triangle K[VAsO(HO)]8HO (in short
V15), (2) the spin ball [MoFeO(MoO(HO))
(MoOH(HO))(CHCOO)(HO)]150HO
(in short Fe30 spin ball), and (3) the twisted triangular spin tube
[(CuCltachH)Cl]Cl (in short Cu3 spin tube).Comment: 13 pages, 14 figure
The suppression of electron correlations in the collapsed tetragonal phase of CaFe2As2 under ambient pressure demonstrated by 75As NMR-NQR measurements
The static and the dynamic spin correlations in the low temperature collapsed
tetragonal and the high temperature tetragonal phase in CaFe2As2 have been
investigated by 75As nuclear magnetic resonance (NMR) and nuclear quadrupole
resonance (NQR) measurements.
Through the temperature (T) dependence of the nuclear spin lattice relaxation
rates (1/T1) and the Knight shifts, although stripe-type antiferromagnetic
(AFM) spin correlations are realized in the high temperature tetragonal phase,
no trace of the AFM spin correlations can be found in the non-superconducting,
low temperature, collapsed tetragonal (cT) phase.
Given that there is no magnetic broadening in 75As NMR spectra, together with
the T-independent behavior of magnetic susceptibility (x) and the T dependence
of 1/T1Tx, we conclude that Fe spin correlations are completely quenched
statically and dynamically in the non-superconducting cT phase in CaFe2As2.Comment: 5 pages, 4 figures, submitted to PR
九鬼周造の人生と哲学
This lecture considers the kinds of problems that existed in Shuzo Kuki\u27s life and how they influenced his philosophy. Centrally, The experience of his mother\u27s misery was crucial to his work on the problem of contingency. When humans who periodically bear such a tragic reality, how can (or should) a person live in that reality ? Kuki\u27s philosophy contains an answer to precisely this question. Kuki concludes that contingency should be understood as fate. Kuki\u27s idea is that through subjective will meaningless contingencies should be given meanings. The lecture concludes by showing how Kuki\u27s philosophy has contemporary significance
Competing Magnetic Fluctuations in Iron Pnictide Superconductors: Role of Ferromagnetic Spin Correlations Revealed by NMR
In the iron pnictide superconductors, theoretical calculations have
consistently shown enhancements of the static magnetic susceptibility at both
the stripe-type antiferromagnetic (AFM) and in-plane ferromagnetic (FM)
wavevectors. However, the possible existence of FM fluctuations has not yet
been examined from a microscopic point of view. Here, using As NMR data,
we provide clear evidence for the existence of FM spin correlations in both the
hole- and electron-doped BaFeAs families of iron-pnictide
superconductors. These FM fluctuations appear to compete with superconductivity
and are thus a crucial ingredient to understanding the variability of and the shape of the superconducting dome in these and other iron-pnictide
families.Comment: 5 pages, 4 figures, accepted for publication in Phys. Rev. Let
NMR Study of the New Magnetic Superconductor CaK(Fe$0.951Ni0.049)4As4: Microscopic Coexistence of Hedgehog Spin-vortex Crystal and Superconductivity
Coexistence of a new-type antiferromagnetic (AFM) state, the so-called
hedgehog spin-vortex crystal (SVC), and superconductivity (SC) is evidenced by
As nuclear magnetic resonance study on single-crystalline
CaK(FeNi)As. The hedgehog SVC order is clearly
demonstrated by the direct observation of the internal magnetic induction along
the axis at the As1 site (close to K) and a zero net internal magnetic
induction at the As2 site (close to Ca) below an AFM ordering temperature
52 K. The nuclear spin-lattice relaxation rate 1/ shows
a distinct decrease below 10 K, providing also unambiguous
evidence for the microscopic coexistence. Furthermore, based on the analysis of
the 1/ data, the hedgehog SVC-type spin correlations are found to be
enhanced below 150 K in the paramagnetic state. These results
indicate the hedgehog SVC-type spin correlations play an important role for the
appearance of SC in the new magnetic superconductor.Comment: 5 pages, 4 figures, accepted for publication in Phys. Rev. B rapid
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