1,817 research outputs found
A view from inside iron-based superconductors
Muon spin spectroscopy is one of the most powerful tools to investigate the
microscopic properties of superconductors. In this manuscript, an overview on
some of the main achievements obtained by this technique in the iron-based
superconductors (IBS) are presented. It is shown how the muons allow to probe
the whole phase diagram of IBS, from the magnetic to the superconducting phase,
and their sensitivity to unravel the modifications of the magnetic and the
superconducting order parameters, as the phase diagram is spanned either by
charge doping, by an external pressure or by introducing magnetic and
non-magnetic impurities. Moreover, it is highlighted that the muons are unique
probes for the study of the nanoscopic coexistence between magnetism and
superconductivity taking place at the crossover between the two ground-states.Comment: 28 pages, 18 figure
Short note on magnetic impurities in SmFeAsOF (x=0, 0.07) compounds revealed by zero-field As NMR
We have performed zero-field As nuclear magnetic resonance study of
SmFeAsOF (x=0, 0.07) polycrystals in a wide frequency range at
various temperatures. As resonance line was found at around 265 MHz
revealing the formation of the intermetallic FeAs clusters in the new layered
superconductors. We have also demonstrated that NMR is a sensitive tool for
probing the quality of these materials.Comment: Revised authorshi
Evidence for impurity-induced frustration in La2CuO4
Zero-field muon spin rotation and magnetization measurements were performed
in La2Cu{1-x}MxO4, for 0<x< 0.12, where Cu2+ is replaced either by M=Zn2+ or by
M=Mg2+ spinless impurity. It is shown that while the doping dependence of the
sublattice magnetization (M(x)) is nearly the same for both compounds, the
N\'eel temperature (T_N(x)) decreases unambiguously more rapidly in the
Zn-doped compound. This difference, not taken into account within a simple
dilution model, is associated with the frustration induced by the Zn2+ impurity
onto the Cu2+ antiferromagnetic lattice. In fact, from T_N(x) and M(x) the spin
stiffness is derived and found to be reduced by Zn doping more significantly
than expected within a dilution model. The effect of the structural
modifications induced by doping on the exchange coupling is also discussed.Comment: 4 pages, 4 figure
Modification of magnetic and transport properties of manganite layers in Au/La_0.67Sr_0.33MnO_3/SrTiO_3 interfaces
The effect of gold capping on magnetic and transport properties of optimally
doped manganite thin films is studied. An extraordinary suppression of
conductivity and magnetic properties occurs in epitaxial (001)
La_0.67Sr_0.33MnO_3 (LSMO) films grown on SrTiO_3 upon deposition of 2 nm of
Au: in the case of ultrathin films of LSMO (4 nm thick) the resistivity
increases by four orders of magnitude while the Curie temperature decreases by
180 K. Zero-field 55Mn nuclear magnetic resonance reveals a significant
reduction of ferromagnetic double-exchange mechanism in manganite films upon
the gold capping. We find evidence for the formation of a 1.9-nm thick magnetic
"dead-layer" at the Au/LSMO interface, associated with the creation of
interfacial non double-exchange insulating phases.Comment: 4 figure
Critical chain length and superconductivity emergence in oxygen-equalized pairs of YBa2Cu3O6.30
The oxygen-order dependent emergence of superconductivity in YBa2Cu3O6+x is
studied, for the first time in a comparative way, on pair samples having the
same oxygen content and thermal history, but different Cu(1)Ox chain
arrangements deriving from their intercalated and deintercalated nature.
Structural and electronic non-equivalence of pairs samples is detected in the
critical region and found to be related, on microscopic scale, to a different
average chain length, which, on being experimentally determined by nuclear
quadrupole resonance (NQR), sheds new light on the concept of critical chain
length for hole doping efficiency.Comment: 7 RevTex pages, 2 Postscript figures. Submitted to Phys. Rev.
Magnetic order in double-layer manganites (La(1-z)Pr(z))1.2Sr1.8Mn2O7: intrinsic properties and role of the intergrowths
We report on an investigation of the double-layer manganite series
(La(1-z)Pr(z))1.2Sr1.8Mn2O7 (0 <= z <= 1), carried out on single crystals by
means of both macroscopic magnetometry and local probes of magnetism (muSR,
55Mn NMR). Muons and NMR demonstrate an antiferromagnetically ordered ground
state at non-ferromagnetic compositions (z >= 0.6), while more moderate Pr
substitutions (0.2 <= z <= 0.4) induce a spin reorientation transition within
the ferromagnetic phase.
A large magnetic susceptibility is detected at {Tc,TN} < T < 250K at all
compositions. From 55Mn NMR spectroscopy, such a response is unambiguously
assigned to the intergrowth of a ferromagnetic pseudocubic phase
(La(1-z)Pr(z))(1-x)Sr(x)MnO3, with an overall volume fraction estimated as
0.5-0.7% from magnetometry. Evidence is provided for the coupling of the
magnetic moments of these inclusions with the magnetic moments of the
surrounding (La(1-z)Pr(z))1.2Sr1.8Mn2O7 phase, as in the case of finely
dispersed impurities. We argue that the ubiquitous intergrowth phase may play a
role in the marked first-order character of the magnetic transition and the
metamagnetic properties above Tc reported for double-layer manganites.Comment: 11 pages, 9 figures. Submitted to Phys. Rev.
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
The poisoning effect of Mn in LaFe(1-x)Mn(x)AsO(0.89)F(0.11): unveiling a quantum critical point in the phase diagram of iron-based superconductors
A superconducting-to-magnetic transition is reported for
LaFeMnAsOF where a per thousand amount of Mn
impurities is dispersed. By employing local spectroscopic techniques like muon
spin rotation (muSR) and nuclear quadrupole resonance (NQR) on compounds with
Mn contents ranging from x=0.025% to x=0.75%, we find that the electronic
properties are extremely sensitive to the Mn impurities. In fact, a small
amount of Mn as low as 0.2% suppresses superconductivity completely. Static
magnetism, involving the FeAs planes, is observed to arise for x > 0.1% and
becomes further enhanced upon increasing Mn substitution. Also a progressive
increase of low energy spin fluctuations, leading to an enhancement of the NQR
spin-lattice relaxation rate 1/T1, is observed upon Mn substitution. The
analysis of 1/T1 for the sample closest to the the crossover between
superconductivity and magnetism (x = 0.2%) points towards the presence of an
antiferromagnetic quantum critical point around that doping level.Comment: 11 pages, 10 figure
Effect of external pressure on the magnetic properties of CoAsO ( = La, Pr, Sm): a SR study
We report on a detailed investigation of the itinerant ferromagnets LaCoAsO,
PrCoAsO and SmCoAsO performed by means of muon spin spectroscopy upon the
application of external hydrostatic pressures up to GPa. These
materials are shown to be magnetically hard in view of the weak dependence of
both critical temperatures and internal fields at the muon site on .
In the cases = La and Sm, the behaviour of the internal field is
substantially unaltered up to GPa. A much richer phenomenology is
detected in PrCoAsO instead, possibly associated with a strong dependence
of the statistical population of the two different crystallographic sites for
the muon. Surprisingly, results are notably different from what is observed in
the case of the isostructural compounds CoPO, where the full As/P
substitution is already inducing a strong chemical pressure within the lattice
but is still very effective in further affecting the magnetic properties.Comment: 8 pages, 9 figure
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