Synthesis and crystal growth

Abstract:

We have studied the field-dependent ac magnetic susceptibility of single crystals of Dy2Ti2O7 spin ice along the [111] direction in the temperature range 1.8-7 K. Our data reflect the onset of local spin-ice order in the appearance of different field regimes. In particular, we observe a prominent feature at approximately 1.0 T that is a precursor of the low-temperature metamagnetic transition out of field-induced kagome ice, below which the kinetic constraints imposed by the ice rules manifest themselves in a substantial frequency dependence of the susceptibility. Despite the relatively high temperatures, our results are consistent with a monopole picture, and they demonstrate that such a picture can give physical insight into spin-ice systems even outside the low-temperature, low-density limit where monopole excitations are well-defined quasiparticles. © 2012 American Physical Society.

Abstract:

We have measured the spin-wave spectrum of the half-doped bilayer manganite Pr(Ca,Sr)2Mn2O7 in its spin, charge, and orbital ordered phase. The measurements, which extend throughout the Brillouin zone and cover the entire one-magnon spectrum, are compared critically with spin-wave calculations for different models of the electronic ground state. The data are described very well by the Goodenough model, which has weakly interacting ferromagnetic zig-zag chains in the CE-type arrangement. A model that allows ferromagnetic dimers to form within the zigzags is inconsistent with the data. The analysis conclusively rules out the strongly bound dimer (Zener polaron) model. © 2012 American Physical Society.

Abstract:

We report strongly momentum-dependent local charge screening dynamics in CE-type charge, orbital, and spin ordered La$_{0.5}$Sr$_{1.5}$MnO$_4$, based on Mn K-edge resonant inelastic x-ray scattering data. Through a comparison with theoretical calculations, we show that the observed momentum dependence reflects highly localized, nearest neighbor screening of the transient local charge perturbation in this compound with an exciton-like screening cloud, rather than delocalized screening. The size of the screening cloud is estmated to be about 0.4-0.5 interatomic distances.

Abstract:

The low-energy electronic structure of the J eff=1/2 spinorbit insulator Sr 3Ir 2O 7 has been studied by means of angle-resolved photoemission spectroscopy. A comparison of the results for bilayer Sr 3Ir 2O 7 with available literature data for the related single-layer compound Sr2IrO4 reveals qualitative similarities and similar J eff=1/2 bandwidths for the two materials, but also pronounced differences in the distribution of the spectral weight. In particular, photoemission from the J eff=1/2 states appears to be suppressed. Yet, it is found that the Sr 3Ir 2O 7 data are in overall better agreement with band-structure calculations than the data for Sr 2IrO 4. © 2012 IOP Publishing Ltd.

Abstract:

We have investigated the spin dynamics of Tb 2Ti 2O 7 as a function of magnetic field applied along the [111] axis using ac susceptibilty and muon-spin relaxation measurements. We find a significant increase in the imaginary part of the magnetic susceptibility at low fields at our lowest investigated temperature and an increased muon-spin relaxation rate in the same field range persisting to higher temperature. Comparing the data from the two techniques we identify three field regions where the dynamic properties of Tb 2Ti 2O 7 appear to be evolving in different ways with crossovers between the regions at B 1=15 and B 2∼60 mT. © 2012 American Physical Society.