Comment on "Magnetoelastic model for the relaxation of lanthanide ions in YBa2Cu3O7-d observed by neutron scattering"

Lovesey and Staub have argued [S.W. Lovesey and U. Staub, Phys. Rev. B 61, 9130 (2000)] that experimental data on the temperature dependence of the paramagnetic relaxation of lanthanide ions doped into YBa2Cu3O6+x are in agreement with the predictions of a model that describes the relaxation as due to the scattering of phonons via a magnetoelastic interaction. By generalising their model I show that the level of agreement is strongly dependent on the number of intermediate lanthanide energy levels included in the calculation, and that inclusion of a more complete set of levels leads to very different results that do not necessarily support the phonon damping picture.Comment: 4 pages, 2 figures, to be published in Phys. Rev.

Approaching the quantum critical point in a highly-correlated all-in-all-out antiferromagnet

Continuous quantum phase transition involving all-in–all-out (AIAO) antiferromagnetic order in strongly spin-orbit-coupled 5d compounds could give rise to various exotic electronic phases and strongly-coupled quantum critical phenomena. Here we experimentally trace the AIAO spin order in Sm₂Ir₂O₇ using direct resonant x-ray magnetic diffraction techniques under high pressure. The magnetic order is suppressed at a critical pressure P_c=6.30GPa, while the lattice symmetry remains in the cubic Fd−3m space group across the quantum critical point. Comparing pressure tuning and the chemical series R₂Ir₂O₇ reveals that the approach to the AIAO quantum phase transition is characterized by contrasting evolutions of the pyrochlore lattice constant a and the trigonal distortion surrounding individual Ir moments, which affects the 5d bandwidth and the Ising anisotropy, respectively. We posit that the opposite effects of pressure and chemical tuning lead to spin fluctuations with different Ising and Heisenberg character in the quantum critical region. Finally, the observed low pressure scale of the AIAO quantum phase transition in Sm₂Ir₂O₇ identifies a circumscribed region of P-T space for investigating the putative magnetic Weyl semimetal state

Spin reorientation transition in the incommensurate stripe-ordered phase of La3/2Sr1/2NiO4

The spin ordering of La3/2Sr1/2NiO4 was investigated by magnetization measurements, and by unpolarized- and polarized-neutron diffraction. Spin ordering with an incommensurability epsilon ~ 0.445 is observed below T_so ~ 80 K. On cooling, a spin reorientation is observed at 57 +/- 1 K, with the spin axes rotating from 52 +/- 4 degrees to 78 +/- 3 degrees. This is the first time a spin reorientation has been observed in a La2-xSrxNiO4+delta compound having incommensurate stripe order.Comment: REVTex 4. 4 pages including 4 figures. Minor changes to text. Accepted to be published in Physical Review

Paramagnon dispersion in β\beta-FeSe observed by Fe LL-edge resonant inelastic x-ray scattering

We report an Fe $L$-edge resonant inelastic x-ray scattering (RIXS) study of the unusual superconductor $\beta$-FeSe. The high energy resolution of this RIXS experiment ($\approx\,$55$\,$meV FWHM) made it possible to resolve low-energy excitations of the Fe $3d$ manifold. These include a broad peak which shows dispersive trends between 100-200$\,$meV along the $(\pi,0)$ and $(\pi,\pi)$ directions of the one-Fe square reciprocal lattice, and which can be attributed to paramagnon excitations. The multi-band valence state of FeSe is among the most metallic in which such excitations have been discerned by soft x-ray RIXS

Magnetic spectrum of the two-dimensional antiferromagnet La2CoO4 studied by inelastic neutron scattering

We report measurements of the magnetic excitation spectrum of the layered antiferromagnet La2CoO4 by time-of-flight neutron inelastic scattering. In the energy range probed in our experiments (0-250 meV) the magnetic spectrum consists of spin-wave modes with strong in-plane dispersion extending up to 60 meV, and a nearly dispersionless peak at 190 meV. The spin-wave modes exhibit a small (~1 meV) dispersion along the magnetic zone boundary. We show that the magnetic spectrum can be described very well by a model of a Heisenberg antiferromagnet that includes the full spin and orbital degrees of freedom of Co2+ in an axially-distorted crystal field. The collective magnetic dynamics are found to be controlled by dominant nearest-neighbour exchange interactions, strong XY-like single-ion anisotropy and a substantial unquenched orbital angular momentum.Comment: 8 pages, 7 figure

The Temperature Evolution of the Out-of-Plane Correlation Lengths of Charge-Stripe Ordered La(1.725)Sr(0.275)NiO(4)

The temperature dependence of the magnetic order of stripe-ordered La(1.725)Sr(0.275)NiO(4) is investigated by neutron diffraction. Upon cooling, the widths if the magnetic Bragg peaks are observed to broaden. The degree of broadening is found to be very different for l = odd-integer and l = even-integer magnetic peaks. We argue that the observed behaviour is a result of competition between magnetic and charge order.Comment: 3 figure

Absence of strong magnetic fluctuations in the iron phosphide superconductors LaFePO and Sr2ScO3FeP

We report neutron inelastic scattering measurements on polycrystalline LaFePO and Sr2ScO3FeP, two members of the iron phosphide families of superconductors. No evidence is found for any magnetic fluctuations in the spectrum of either material in the energy and wavevector ranges probed. Special attention is paid to the wavevector at which spin-density-wave-like fluctuations are seen in other iron-based superconductors. We estimate that the magnetic signal, if present, is at least a factor of four (Sr2ScO3FeP) or seven (LaFePO) smaller than in the related iron arsenide and chalcogenide superconductors. These results suggest that magnetic fluctuations are not as influential on the electronic properties of the iron phosphide systems as they are in other iron-based superconductors.Comment: 7 pages, 5 figure

Phonon Dispersion Relations in PrBa2Cu3O6+x (x ~ 0.2)

We report measurements of the phonon dispersion relations in non-superconducting, oxygen-deficient PrBa2Cu3O6+x (x ~ 0.2) by inelastic neutron scattering. The data are compared with a model of the lattice dynamics based on a common interaction potential. Good agreement is achieved for all but two phonon branches, which are significantly softer than predicted. These modes are found to arise predominantly from motion of the oxygen ions in the CuO2 planes. Analogous modes in YBa2Cu3O6 are well described by the common interaction potential model.Comment: 4 pages, 3 figures. Minor changes following referees' comment