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Finger T.,University of Cologne | Senff D.,University of Cologne | Schmalzl K.,Julich Research Center | Schmidt W.,Julich Research Center | And 4 more authors.
Journal of Physics: Conference Series | Year: 2010

Neutron diffraction with spherical polarization analysis is a powerful tool for studying the multiferroic materials where the ferroelectric polarization arises from a complex magnetic structure. Analyzing the off-diagonal terms in the polarization matrix one may directly detect the chiral contributions even in a multidomain arrangement. In MnWO4 one can control the chiral magnetism by varying an electric field at constant temperature. The analysis of multiferroic hysteresis cycles at four equivalent magnetic Bragg peaks fully agrees with a nearly monodomain chiral arrangement controlled by the electric field. A pronounced asymmetry of the hysteresis cycles and memory effects point to strong pinning of the chiral magnetism in MnWO4. We find a second-order harmonic modulation which exhibits both magnetic and structural character and which may be related with the domain pinning. The observed interference between the nuclear and the magnetic modulation is another manifestation of the coupling between the crystal structure and the magnetism in the multiferroic oxides. © 2010 IOP Publishing Ltd. Source


Dalmas De Reotier P.,Institute Nanosciences et Cryogenie | Yaouanc A.,Institute Nanosciences et Cryogenie
Physical Review B - Condensed Matter and Materials Physics | Year: 2011

We compute the form factor and the standard deviation and skewness of the field distribution for a hard type-II heavy-fermion superconductor using an approximate analytical solution of the Ginzburg-Landau model. Our results are relevant if the temperature is such that T>T *=0.56T c, where T c is the superconductivity temperature. Instead of decreasing monotonically as the field is ramped up to the upper critical field as usually found, reflecting the influence of the Zeeman currents the form factor and standard deviation are predicted to display a maximum at an intermediate applied field intensity if the effective electron mass is sufficiently large. This behavior has been observed for the CeCoIn 5 form factor at TT * and is explained qualitatively by our computation. Contrary to the form factor and standard deviation, the skewness of the field distribution is not strongly influenced by the Zeeman currents. © 2011 American Physical Society. Source


Yaouanc A.,Institute Nanosciences et Cryogenie | Dalmas De Reotier P.,Institute Nanosciences et Cryogenie | Chapuis Y.,Institute Nanosciences et Cryogenie | Marin C.,Institute Nanosciences et Cryogenie | And 8 more authors.
Physical Review B - Condensed Matter and Materials Physics | Year: 2011

The insulator pyrochlore Tb2Ti2O7 is a three-dimensional spin liquid candidate: the strength of the magnetic interaction would normally induce order at 20 K, but according to published muon-spin relaxation and neutron diffraction measurements, it is still in a correlated paramagnetic state down to a temperature of 0.05 K. Our detailed experimental investigation shows that an exotic transition takes place at T t=0.15(2) K. It is characterized by an anomaly in the muon precession frequency shift but not in the specific heat, which nevertheless reveals the signature of degrees of freedom at very low energy. It might be associated with a cooperative Jahn-Teller transition. The robustness of the experimental results is discussed. © 2011 American Physical Society. Source


Rodriguez J.A.,Paul Scherrer Institute | Yaouanc A.,Paul Scherrer Institute | Yaouanc A.,Institute Nanosciences et Cryogenie | Barbara B.,CNRS Neel Institute | And 3 more authors.
Physical Review B - Condensed Matter and Materials Physics | Year: 2013

We report a muon spin relaxation study in a Y2Ti 2O7 single crystal. We observe slow local field fluctuations at low temperature which become faster as the temperature is increased. Our analysis suggests that muon diffusion is present in this system and it is small below 40 K and therefore incoherent. A surprisingly strong electronic magnetic signal is observed with features typical for muons thermally diffusing towards magnetic traps below ≈100 K and released from them above this temperature. We attribute the traps to Ti3+ defects in the diluted limit. Our observations are highly relevant to the persistent spin dynamics debate on R2Ti2O7 pyrochlores and their crystal quality. © 2013 American Physical Society. Source

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