1,662 research outputs found
High pressure magnetic state of MnP probed by means of muon-spin rotation
We report a detailed SR study of the pressure evolution of the magnetic
order in the manganese based pnictide MnP, which has been recently found to
undergo a superconducting transition under pressure once the magnetic ground
state is suppressed. Using the muon as a volume sensitive local magnetic probe,
we identify a ferromagnetic state as well as two incommensurate helical states
(with propagation vectors aligned along the crystallographic and
directions, respectively) which transform into each other through first
order phase transitions as a function of pressure and temperature. Our data
appear to support that the magnetic state from which superconductivity develops
at higher pressures is an incommensurate helical phase.Comment: 11 pages, 9 figure
Soft x-rays absorption and high-resolution powder x-ray diffraction study of superconducting CaxLa(1-x)Ba(1.75-x)La(0.25+x)Cu3Oy system
We have studied the electronic structure of unoccupied states measured by O
K-edge and Cu L-edge x-ray absorption spectroscopy (XAS), combined with crystal
structure studied by high resolution powder x-ray diffraction (HRPXRD), of
charge-compensated layered superconducting CaxLa(1-x)Ba(1.75-x)La(0.25+x)Cu3Oy
(0<x<0.4, 6.4<y<7.3) cuprate. A detailed analysis shows that, apart from hole
doping, chemical pressure on the electronically active CuO2 plane due to the
lattice mismatch with the spacer layers greatly influences the superconducting
properties of this system. The results suggest chemical pressure to be the most
plausible parameter to control the maximum critical temperatures (Tcmax) in
different cuprate families at optimum hole density.Comment: 14 pages, 11 figures, accepted for publication in Journal of Physics
and Chemistry of Solid
Magnetic ground state and spin fluctuations in MnGe chiral magnet as studied by Muon Spin Rotation
We have studied by muon spin resonance ({\mu}SR) the helical ground state and
fluctuating chiral phase recently observed in the MnGe chiral magnet. At low
temperature, the muon polarization shows double period oscillations at short
time scales. Their analysis, akin to that recently developed for MnSi [A. Amato
et al., Phys. Rev. B 89, 184425 (2014)], provides an estimation of the field
distribution induced by the Mn helical order at the muon site. The refined muon
position agrees nicely with ab initio calculations. With increasing
temperature, an inhomogeneous fluctuating chiral phase sets in, characterized
by two well separated frequency ranges which coexist in the sample. Rapid and
slow fluctuations, respectively associated with short range and long range
ordered helices, coexist in a large temperature range below T = 170 K. We
discuss the results with respect to MnSi, taking the short helical period,
metastable quenched state and peculiar band structure of MnGe into account.Comment: 13 pages, 11 figure
Slow magnetic fluctuations and superconductivity in fluorine-doped NdFeAsO
Among the widely studied superconducting iron-pnictide compounds belonging to
the Ln1111 family (with Ln a lanthanide), a systematic investigation of the
crossover region between the superconducting and the antiferromagnetic phase
for the Ln = Nd case has been missing. We fill this gap by focusing on the
intermediate doping regime of NdFeAsO(1-x)F(x) by means of dc-magnetometry and
muon-spin spectroscopy measurements. The long-range order we detect at low
fluorine doping is replaced by short-range magnetic interactions at x = 0.08,
where also superconductivity appears. In this case, longitudinal-field
muon-spin spectroscopy experiments show clear evidence of slow magnetic
fluctuations that disappear at low temperatures. This fluctuating component is
ascribed to the glassy-like character of the magnetically ordered phase of
NdFeAsO at intermediate fluorine doping
Magnetic glassy phase in FeSeTe single crystals
The evolution of the magnetic order in FeSeTe crystals as a function of Se
content was investigated by means of ac/dc magnetometry and muon-spin
spectroscopy. Experimental results and self-consistent DFT calculations both
indicate that muons are implanted in vacant iron-excess sites, where they probe
a local field mainly of dipolar origin, resulting from an antiferromagnetic
(AFM) bicollinear arrangement of iron spins. This long-range AFM phase
disorders progressively with increasing Se content. At the same time all the
tested samples manifest a marked glassy character that vanishes for high Se
contents. The presence of local electronic/compositional inhomogeneities most
likely favours the growth of clusters whose magnetic moment "freezes" at low
temperature. This glassy magnetic phase justifies both the coherent muon
precession seen at short times in the asymmetry data, as well as the glassy
behaviour evidenced by both dc and ac magnetometry.Comment: Approved for publication in J. Phys.: Condens. Matte
Fast recovery of the stripe magnetic order by Mn/Fe substitution in F-doped LaFeAsO superconductors
As Nuclear Magnetic (NMR) and Quadrupolar (NQR) Resonance were used,
together with M\"{o}ssbauer spectroscopy, to investigate the magnetic state
induced by Mn for Fe substitutions in F-doped LaFeMnAsO
superconductors. The results show that % of Mn doping is enough to
suppress the superconducting transition temperature from 27 K to zero and
to recover the magnetic structure observed in the parent undoped LaFeAsO. Also
the tetragonal to orthorhombic transition of the parent compound is recovered
by introducing Mn, as evidenced by a sharp drop of the NQR frequency. The NQR
spectra also show that a charge localization process is at play in the system.
Theoretical calculations using a realistic five-band model show that
correlation-enhanced RKKY exchange interactions between nearby Mn ions
stabilize the observed magnetic order, dominated by and
ordering vectors. These results give compelling evidence that
F-doped LaFeAsO is a strongly correlated electron system at the verge of an
electronic instability.Comment: 5 pages, 5 figures and 4 pages of supplemental materia
Tuning of competing magnetic and superconducting phase volumes in LaFeAsO$_0.945F_0.055 by hydrostatic pressure
The interplay between magnetism and superconductivity in LaFeAsO_0.945F_0.055
was studied as a function of hydrostatic pressure up to p~2.4GPa by means of
muon-spin rotation (\muSR) and magnetization measurements. The application of
pressure leads to a substantial decrease of the magnetic ordering temperature
T_N and a reduction of the magnetic phase volume and, at the same time, to a
strong increase of the superconducting transition temperature T_c and the
diamagnetic susceptibility. From the volume sensitive \muSR measurements it can
be concluded that the superconducting and the magnetic areas which coexist in
the same sample are inclined towards spatial separation and compete for phase
volume as a function of pressure.Comment: 4 pages, 4 figure
Evidence of orbital reconstruction at interfaces in La0.67Sr0.33MnO3 films
Electronic properties of transition metal oxides at interfaces are influenced
by strain, electric polarization and oxygen diffusion. Linear dichroism (LD)
x-ray absorption, diffraction, transport and magnetization on thin
La0.7Sr0.3MnO3 films, allow identification of a peculiar universal interface
effect. We report the LD signature of preferential 3d-eg(3z2-r2) occupation at
the interface, suppressing the double exchange mechanism. This surface orbital
reconstruction is opposite of that favored by residual strain and independent
of dipolar fields, chemical nature of the substrate and capping.Comment: 13 pages, 5 figure
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