53 research outputs found
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
Tuning the magnetic and structural phase transitions of PrFeAsO via Fe/Ru spin dilution
Neutron diffraction and muon spin relaxation measurements are used to obtain
a detailed phase diagram of Pr(Fe,Ru)AsO. The isoelectronic substitution of Ru
for Fe acts effectively as spin dilution, suppressing both the structural and
magnetic phase transitions. The temperature of the tetragonal-orthorhombic
structural phase transition decreases gradually as a function of x. Slightly
below the transition temperature coherent precessions of the muon spin are
observed corresponding to static magnetism, possibly reflecting a significant
magneto-elastic coupling in the FeAs layers. Short range order in both the Fe
and Pr moments persists for higher levels of x. The static magnetic moments
disappear at a concentration coincident with that expected for percolation of
the J1-J2 square lattice model
Magnetic properties of spin diluted iron pnictides from muSR and NMR in LaFe1-xRuxAsO
The effect of isoelectronic substitutions on the microscopic properties of
LaFe1-xRuxAsO, for 0< x< 0.8, has been investigated by means of muSR and 139La
NMR. It was found that Ru substitution causes a progressive reduction of the
N\`eel temperature (T_N) and of the magnetic order parameter without leading to
the onset of superconductivity. The temperature dependence of 139La nuclear
spin-lattice relaxation rate 1/T_1 can be suitably described within a two-band
model. One band giving rise to the spin density wave ground-state, while the
other one is characterized by weakly correlated electrons. Fe for Ru
substitution yields to a progressive decrease of the density of states at the
Fermi level close to the one derived from band structure calculations. The
reduction of T_N with doping follows the predictions of the J_1-J_2 model on a
square lattice, which appears to be an effective framework to describe the
magnetic properties of the spin density wave ground-state.Comment: 6 pages, 8 figure
Entanglement between Muon and I > 1/2 Nuclear Spins as a Probe of Charge Environment
We report on the first example of quantum coherence between the spins of muons and quadrupolar nuclei. We reveal that these entangled states are highly sensitive to a local charge environment and thus, can be deployed as a functional quantum sensor of that environment. The quantum coherence effect was observed in vanadium intermetallic compounds which adopt the A15 crystal structure, and whose members include all technologically pertinent superconductors. Furthermore, the extreme sensitivity of the entangled states to the local structural and electronic environments emerges through the quadrupolar interaction with the electric field gradient due to the charge distribution at the nuclear (I >1/2) sites. This case study demonstrates that positive muons can be used as a quantum sensing tool to also probe structural and charge-related phenomena in materials, even in the absence of magnetic degrees of freedom
Spin-orbital Jahn-Teller bipolarons
Polarons and spin-orbit (SO) coupling are distinct quantum effects that play
a critical role in charge transport and spin-orbitronics. Polarons originate
from strong electron-phonon interaction and are ubiquitous in polarizable
materials featuring electron localization, in particular
transition metal oxides (TMOs). On the other hand, the relativistic coupling
between the spin and orbital angular momentum is notable in lattices with heavy
atoms and develops in TMOs, where electrons are spatially
delocalized. Here we combine ab initio calculations and magnetic measurements
to show that these two seemingly mutually exclusive interactions are entangled
in the electron-doped SO-coupled Mott insulator
(), unveiling the formation of
spin-orbital bipolarons. Polaron charge trapping, favoured by the Jahn-Teller
lattice activity, converts the Os spin-orbital
levels, characteristic of the parent compound
(BNOO), into a bipolaron
manifold, leading to the coexistence of different
J-effective states in a single-phase material. The gradual increase of
bipolarons with increasing doping creates robust in-gap states that prevents
the transition to a metal phase even at ultrahigh doping, thus preserving the
Mott gap across the entire doping range from BNOO to
(BCOO)
Effect of external pressure on the magnetic properties of LnFeAsO (Ln = La, Ce, Pr, Sm)
We investigate the effect of external pressure on magnetic order in undoped
LnFeAsO (Ln = La, Ce, Pr, La) by using muon-spin relaxation measurements and
ab-initio calculations. Both magnetic transition temperature and Fe
magnetic moment decrease with external pressure. The effect is observed to be
lanthanide dependent with the strongest response for Ln = La and the weakest
for Ln = Sm. The trend is qualitatively in agreement with our DFT calculations.
The same calculations allow us to assign a value of 0.68(2) to the Fe
moment, obtained from an accurate determination of the muon sites. Our data
further show that the magnetic lanthanide order transitions do not follow the
simple trend of Fe, possibly as a consequence of the different -electron
overlap.Comment: 16 pages, 11 figure
Planck Intermediate Results. XXXVI. Optical identification and redshifts of Planck SZ sources with telescopes at the Canary Islands Observatories
We present the results of approximately three years of observations of Planck
Sunyaev-Zeldovich (SZ) sources with telescopes at the Canary Islands
observatories as part of the general optical follow-up programme undertaken by
the Planck collaboration. In total, 78 SZ sources are discussed. Deep-imaging
observations were obtained for most of these sources; spectroscopic
observations in either in long-slit or multi-object modes were obtained for
many. We effectively used 37.5 clear nights. We found optical counterparts for
73 of the 78 candidates. This sample includes 53 spectroscopic redshift
determinations, 20 of them obtained with a multi-object spectroscopic mode. The
sample contains new redshifts for 27 Planck clusters that were not included in
the first Planck SZ source catalogue (PSZ1).Comment: 15 pages, 14 figures, accepted for publication in A&
VizieR Online Data Catalog: 1Jy northern AGN sample (Planck+, 2016)
The complete sample presented in this paper consists of 104 northern and equatorial radio-loud AGN. It includes all AGN with declination >=-10° that have a measured average radio flux density at 37GHz exceeding 1Jy. Most of the sample sources have been monitored at Metsahovi Radio Observatory for many years, and the brightest sources have been observed for up to 30yr. (1 data file)
VizieR Online Data Catalog: Planck high-z source candidates catalog (PHZ) (Planck+, 2016)
We present in this work the Planck List of Highredshift Source Candidates (the "PHZ"), which includes 2151 sources distributed over 26% of the sky, with redshifts likely to be greater than 2. (2 data files)
VizieR Online Data Catalog: Planck Catalogue of Galactic cold clumps (PGCC) (Planck+, 2016)
The Planck Catalogue of Galactic Cold Clumps (PGCC) is a list of 13188 Galactic sources and 54 sources located in the Small and Large Magellanic Clouds. The sources have been identified in Planck data as sources colder than their environment. It has been built using the 48 months Planck data at 857, 545, and 353GHz combined with the 3THz IRAS data. (1 data file)
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