arXiv subjects

K. Prokes

Publications and source records attributed to K. Prokes.

26 records · Page 2Linked to original sources

arXiv2005

Novel Coexistence of Superconductivity with Two Distinct Magnetic Orders

The heavy fermion Ce(Rh,Ir)In5 system exhibits properties that range from an incommensurate antiferromagnet on the Rh-rich end to an exotic superconductor on the Ir-rich end of the phase diagram. At intermediate composition where antiferromagnetism coexists with superconductivity, two types of magnetic order are observed: the incommensurate one of CeRhIn5 and a new, commensurate antiferromagnetism that orders separately. The coexistence of f-electron superconductivity with two distinct f-electron magnetic orders is unique among unconventional superconductors, adding a new variety to the usual coexistence found in magnetic superconductors.

cond-mat.supr-con↗

arXiv2004

Field-Induced Magnetic and Structural Domain Alignment in PrO2

We present a neutron diffraction study of the magnetic structure of single crystal PrO2 under applied fields of 0-6 T. As the field is increased, changes are observed in the magnetic Bragg intensities. These changes are found to be irreversible when the field is reduced, but the original intensities can be recovered by heating to T > 122 K, then re-cooling in zero field. The antiferromagnetic ordering temperature TN = 13.5 K and the magnetic periodicity are unaffected by the applied field. We also report measurements of the magnetic susceptibility of single crystal PrO2 under applied fields of 0-7 T. These show strong anisotropy, as well as an anomaly at T = 122 +/- 2 K which coincides with the temperature TD = 120 +/- 2 K at which a structural distortion occurs. For fields applied along the [100] direction the susceptibility increases irreversibly with field in the temperature range TN < T < TD. However, for fields along [110] the susceptibility is independent of field in this range. We propose structural domain alignment, which strongly influences the formation of magnetic domains below TN, as the mechanism behind these changes.

cond-mat.str-el↗

arXiv2004

Phase Decomposition and Chemical Inhomogeneity in Nd2-xCexCuO4

Extensive X-ray and neutron scattering experiments and additional transmission electron microscopy results reveal the partial decomposition of Nd2-xCexCuO4 (NCCO) in a low-oxygen-fugacity environment such as that typically realized during the annealing process required to create a superconducting state. Unlike a typical situation in which a disordered secondary phase results in diffuse powder scattering, a serendipitous match between the in-plane lattice constant of NCCO and the lattice constant of one of the decomposition products, (Nd,Ce)2O3, causes the secondary phase to form an oriented, quasi-two-dimensional epitaxial structure. Consequently, diffraction peaks from the secondary phase appear at rational positions (H,K,0) in the reciprocal space of NCCO. Additionally, because of neodymium paramagnetism, the application of a magnetic field increases the low-temperature intensity observed at these positions via neutron scattering. Such effects may mimic the formation of a structural superlattice or the strengthening of antiferromagnetic order of NCCO, but the intrinsic mechanism may be identified through careful and systematic experimentation. For typical reduction conditions, the (Nd,Ce)2O3 volume fraction is ~1%, and the secondary-phase layers exhibit long-range order parallel to the NCCO CuO2 sheets and are 50-100 angstromsthick. The presence of the secondary phase should also be taken into account in the analysis of other experiments on NCCO, such as transport measurements.

cond-mat.supr-con↗

arXiv2003

Effect of a magnetic field on the long-range magnetic order in insulating Nd2CuO4, nonsuperconducting and superconducting Nd1.85Ce0.15CuO4

We have measured the effect of a c-axis aligned magnetic field on the long-range magnetic order of insulating Nd2CuO4, as-grown nonsuperconducting and superconducting Nd1.85Ce0.15CuO4. On cooling from room temperature, Nd2CuO4 goes through a series of antiferromagnetic (AF) phase transitions with different noncollinear spin structures. In all phases of Nd2CuO4, we find that the applied c-axis field induces a canting of the AF order but does not alter the basic zero-field noncollinear spin structures. Similar behavior is also found in as-grown nonsuperconducting Nd1.85Ce0.15CuO4. These results contrast dramatically with those of superconducting Nd1.85Ce0.15CuO4, where a c-axis aligned magnetic field induces a static, anomalously conducting, long-range ordered AF state. We confirm that the annealing process necessary to make superconducting Nd1.85Ce0.15CuO4 also induces epitaxial, three-dimensional long-range ordered cubic (Nd,Ce)2O3 as an impurity phase. In addition, the annealing process makes a series of quasi two-dimensional superlattice reflections associated with lattice distortions of Nd1.85Ce0.15CuO4 in the CuO2 plane. While the application of a magnetic field will induce a net moment in the impurity phase, we determine its magnitude and eliminate this as a possibility for the observed magnetic field-induced effect in superconducting Nd1.85Ce0.15CuO4.

cond-mat.str-el↗

arXiv2002

Inflection point in the magnetic field dependence of the ordered moment of URu2Si2 observed by neutron scattering in fields up to 17 T

We have measured the magnetic field dependence of the ordered antiferromagnetic moment and the magnetic excitations in the heavy-fermion superconductor URu2Si2 for fields up to 17 Tesla applied along the tetragonal c axis, using neutron scattering. The decrease of the magnetic intensity of the tiny moment with increasing field does not follow a simple power law, but shows a clear inflection point, indicating that the moment disappears first at the metamagnetic transition at ~40 T. This suggests that the moment m is connected to a hidden order parameter Phi which belongs to the same irreducible representation breaking time-reversal symmetry. The magnetic excitation gap at the antiferromagnetic zone center Q=(1,0,0) increases continuously with increasing field, while that at Q=(1.4,0,0) is nearly constant. This field dependence is opposite to that of the gap extracted from specific-heat data.

cond-mat.str-el↗

arXiv2002

Neutron-diffraction study of field-induced transitions in the heavy-fermion compound Ce2RhIn8

We present neutron diffraction measurements in high magnetic fields (0 to 14.5 T) and at low temperatures (2.5, 2.3, 0.77 and 0.068 K) on single crystals of the tetragonal heavy fermion antiferromagnet Ce2RhIn8. For B//[110] the field dependence of selected magnetic and nuclear reflections reveals that the material undergoes several transitions, the temperature dependence of which suggests a complex B-T phase diagram. We present the detailed evolution of the integrated intensities of selected reflections and discuss the associated field-induced transitions.

cond-mat.str-el↗

arXiv2001

Field-induced commensurate long-range order in the Haldane-gap system NDMAZ

High-field neutron diffraction studies of the new quantum-disordered S=1 linear-chain antiferromagnet Ni(C$_5$H$_{14}$N$_2$)$_2$N$_3$(ClO$_4$) (NDMAZ) are reported. At T=70 mK, at a critical field $H_c=13.4$ T applied along the (013) direction, a phase transition to a commensurate Néel-like ordered state is observed. The results are discussed in the context of existing theories of quantum phase transitions in Haldane-gap antiferromagnets, and in comparions with previous studies of the related system Ni(C$_5$H$_{14}$N$_2$)$_2$N$_3$(PF$_6$).

cond-mat.str-el↗

arXiv1999

Neutron scattering study of the field-induced soliton lattice in CuGeO$_3$

CuGeO$_3$ undergoes a transition from a spin-Peierls phase to an incommensurate phase at a critical field of $H_c\approx 12.5$ T. In the high-field phase a lattice of solitons forms, with both structural and magnetic components, and these have been studied using neutron scattering techniques. Our results provide direct evidence for a long-ranged magnetic soliton structure which has both staggered and uniform magnetizations, and with amplitudes that are broadly in accord with theoretical estimates. The magnetic soliton width, $Γ$, and the field dependence of the incommensurability, $δk_{sp}$, are found to agree well with theoretical predictions.

cond-mat↗