Magnetodielectric and magnetoelastic coupling in TbFe3(BO3)4

We have studied the magnetodielectric and magnetoelastic coupling in TbFe3(BO3)4 single crystals by means of capacitance, magnetostriction and Raman spectroscopy measurements. The data reveal strong magnetic field effects on the dielectric constant and on the macroscopic sample length which are associated to long range magnetic ordering and a field-driven metamagnetic transition. We discuss the coupling of the dielectric, structural, and magnetic order parameters and attribute the origin of the magnetodielectric coupling to phonon mode shifts according to the Lyddane-Sachs-Teller (LST) relation.Comment: Accepted for publication in Physical Review

Mutual independence of critical temperature and superfluid density under pressure in optimally electron-doped superconducting LaFeAsO1−x_{1-x}Fx_{x}

The superconducting properties of LaFeAsO$_{1-x}$F$_{x}$ in conditions of optimal electron-doping are investigated upon the application of external pressure up to $\sim 23$ kbar. Measurements of muon-spin spectroscopy and dc magnetometry evidence a clear mutual independence between the critical temperature $T_{c}$ and the low-temperature saturation value for the ratio $n_{s}/m^{*}$ (superfluid density over effective band mass of Cooper pairs). Remarkably, a dramatic increase of $\sim 30$ % is reported for $n_{s}/m^{*}$ at the maximum pressure value while $T_{c}$ is substantially unaffected in the whole accessed experimental window. We argue and demonstrate that the explanation for the observed results must take the effect of non-magnetic impurities on multi-band superconductivity into account. In particular, the unique possibility to modify the ratio between intra-band and inter-bands scattering rates by acting on structural parameters while keeping the amount of chemical disorder constant is a striking result of our proposed model.Comment: 8 pages (Main text: 5 pages. Paper merged with supplemental information), 5 figure

Thermodynamic Properties of the Anisotropic Frustrated Spin-chain Compound Linarite PbCuSO4_4(OH)2_2

We present a comprehensive macroscopic thermodynamic study of the quasi-one-dimensional (1D) $s = \tfrac{1}{2}$ frustrated spin-chain system linarite. Susceptibility, magnetization, specific heat, magnetocaloric effect, magnetostriction, and thermal-expansion measurements were performed to characterize the magnetic phase diagram. In particular, for magnetic fields along the b axis five different magnetic regions have been detected, some of them exhibiting short-range-order effects. The experimental magnetic entropy and magnetization are compared to a theoretical modelling of these quantities using DMRG and TMRG approaches. Within the framework of a purely 1D isotropic model Hamiltonian, only a qualitative agreement between theory and the experimental data can be achieved. Instead, it is demonstrated that a significant symmetric anisotropic exchange of about 10% is necessary to account for the basic experimental observations, including the 3D saturation field, and which in turn might stabilize a triatic (three-magnon) multipolar phase.Comment: 20 pages, 17 figure

Mutual Independence of Critical Temperature and Superfluid Density under Pressure in Optimally Electron-Doped Superconducting LaFeAsO<inf>1-x</inf>F<inf>x</inf>

© 2015 American Physical Society. The superconducting properties of LaFeAsO1-xFx under conditions of optimal electron doping are investigated upon the application of external pressure up to ∼ 23 kbar. Measurements of muon-spin spectroscopy and dc magnetometry evidence a clear mutual independence between the critical temperature Tc and the low-temperature saturation value for the ratio ns/m∗ (superfluid density over effective band mass of Cooper pairs). Remarkably, a dramatic increase of ∼ 30% is reported for ns/m∗ at the maximum pressure value while Tc is substantially unaffected in the whole accessed experimental window. We argue and demonstrate that the explanation for the observed results must take the effect of nonmagnetic impurities on multiband superconductivity into account. In particular, the unique possibility to modify the ratio between intraband and interband scattering rates by acting on structural parameters while keeping the amount of chemical disorder constant is a striking result of our proposed model

Dilatometric study of the metamagnetic and ferromagnetic phases in the triple-layered Sr4Ru3 O10 system

High-resolution thermal expansion and magnetostriction measurements were performed on single crystalline Sr4Ru3O10 in the temperature range T=2-200 K and magnetic fields up to 12 T. Signatures of the ferromagnetic phase transition at Tc∼102 K were found in the lattice expansion of both the c axis and the ab plane. Due to the layered crystal structure the effects are, however, strongly anisotropic. Further distinct anomalies are visible in the lower temperature region, which could be correlated with the metamagnetic transition at T∗∼50 K. By relating the changes of the thermal expansion at the ferromagnetic transition to those of the heat capacity via the Ehrenfest relation, a strong volumetric pressure dependence of dTc/dp∼-8.5 K/GPa has been revealed

Influence of hydrostatic pressure on the bulk magnetic properties of Eu2Ir2O7

We report on the magnetic properties of Eu2Ir2O7 upon the application of hydrostatic pressure P by means of macroscopic and local-probe techniques. In contrast to previously reported resistivity measurements, our dc magnetization data unambiguously demonstrate a nonmonotonic dependence of TN, i.e., the critical transition temperature to the magnetic phase, on P. Strikingly, the recently calculated behavior for TN closely reproduces our results under the assumption that P lowers the U/W ratio (i.e., Coulomb repulsion energy over electronic bandwidth). Zero-field muon-spin spectroscopy measurements confirm that the Ir4+ magnetic moment and/or the local magnetic configuration are only weakly perturbed by low P values. Accordingly, our current experimental findings strongly support the preservation of a 4-in/4-out ground state across the accessed region of the phase diagram

Mutual Independence of Critical Temperature and Superfluid Density under Pressure in Optimally Electron-Doped Superconducting LaFeAsO<inf>1-x</inf>F<inf>x</inf>

© 2015 American Physical Society. The superconducting properties of LaFeAsO1-xFx under conditions of optimal electron doping are investigated upon the application of external pressure up to ∼ 23 kbar. Measurements of muon-spin spectroscopy and dc magnetometry evidence a clear mutual independence between the critical temperature Tc and the low-temperature saturation value for the ratio ns/m∗ (superfluid density over effective band mass of Cooper pairs). Remarkably, a dramatic increase of ∼ 30% is reported for ns/m∗ at the maximum pressure value while Tc is substantially unaffected in the whole accessed experimental window. We argue and demonstrate that the explanation for the observed results must take the effect of nonmagnetic impurities on multiband superconductivity into account. In particular, the unique possibility to modify the ratio between intraband and interband scattering rates by acting on structural parameters while keeping the amount of chemical disorder constant is a striking result of our proposed model

Mutual Independence of Critical Temperature and Superfluid Density under Pressure in Optimally Electron-Doped Superconducting LaFeAsO<inf>1-x</inf>F<inf>x</inf>

© 2015 American Physical Society. The superconducting properties of LaFeAsO1-xFx under conditions of optimal electron doping are investigated upon the application of external pressure up to ∼ 23 kbar. Measurements of muon-spin spectroscopy and dc magnetometry evidence a clear mutual independence between the critical temperature Tc and the low-temperature saturation value for the ratio ns/m∗ (superfluid density over effective band mass of Cooper pairs). Remarkably, a dramatic increase of ∼ 30% is reported for ns/m∗ at the maximum pressure value while Tc is substantially unaffected in the whole accessed experimental window. We argue and demonstrate that the explanation for the observed results must take the effect of nonmagnetic impurities on multiband superconductivity into account. In particular, the unique possibility to modify the ratio between intraband and interband scattering rates by acting on structural parameters while keeping the amount of chemical disorder constant is a striking result of our proposed model

Mutual Independence of Critical Temperature and Superfluid Density under Pressure in Optimally Electron-Doped Superconducting LaFeAsO<inf>1-x</inf>F<inf>x</inf>

© 2015 American Physical Society. The superconducting properties of LaFeAsO1-xFx under conditions of optimal electron doping are investigated upon the application of external pressure up to ∼ 23 kbar. Measurements of muon-spin spectroscopy and dc magnetometry evidence a clear mutual independence between the critical temperature Tc and the low-temperature saturation value for the ratio ns/m∗ (superfluid density over effective band mass of Cooper pairs). Remarkably, a dramatic increase of ∼ 30% is reported for ns/m∗ at the maximum pressure value while Tc is substantially unaffected in the whole accessed experimental window. We argue and demonstrate that the explanation for the observed results must take the effect of nonmagnetic impurities on multiband superconductivity into account. In particular, the unique possibility to modify the ratio between intraband and interband scattering rates by acting on structural parameters while keeping the amount of chemical disorder constant is a striking result of our proposed model

Influence of hydrostatic pressure on the bulk magnetic properties of Eu

We report on the magnetic properties of Eu$_{2}$Ir$_{2}$O$_{7}$ upon the application of hydrostatic pressure $P$ by means of macroscopic and local-probe techniques. In contrast to previously reported resistivity measurements, our dc magnetization data unambiguously demonstrate a non-monotonic $P$-dependence for $T_{N}$, i.~e., the critical transition temperature to the magnetic phase. More strikingly, we closely reproduce the recently calculated behaviour for $T_{N}$ under the assumption that $P$ lowers the $U/W$ ratio (i.~e., Coulomb repulsion energy over electronic bandwidth). Zero-field muon-spin spectroscopy measurements confirm that the local magnetic configuration is only weakly perturbed by low $P$ values, in agreement with theoretical predictions. The current results experimentally support the preservation of a $4$-in/$4$-out ground state and, simultaneously, a departure from the single-band $j_{\text{eff}} = 1/2$ model across the accessed region of the phase diagram.Comment: 13 pages (Main text: 6 pages. Paper merged with supplemental information), 11 figure