B. Roessli

Neutron diffraction study of the heavy fermion superconductors UM2Al3(M=Pd, Ni)

An elastic neutron scattering study was performed on the new superconducting heavy fermion systems UPd2Al3 and UNi2Al3. The neutron diffraction patterns reveal unambiguously long range antiferromagnetic order in UPd2Al3 with an ordered magnetic momentμU = (0.85±0.03)μB, which coexists with the superconducting state. This is by far the largestμU value observed for any heavy fermion superconductor. For UNi2Al3, no long-range magnetic order could be observed for temperaturesT≧1.5 K, yielding an upper limit of the ordered moment of 0.2μB.

A systematic low-temperature neutron diffraction study of the RBa2Cu3Ox (R=yttrium and rare earths; x=6 and 7) compounds

The crystal structures of RBa2Cu3Ox (R=Y and rare earths; x=6 and 7) ceramic materials were investigated at 10 K by neutron diffraction and consistently analysed concerning systematic trends. Other than for non-superconducting PrBa2Cu3O7 the lattice parameters and most interionic distances exhibit the well known lanthanide contraction behaviour, i.e., a linear relationship with the ionic radii of trivalent rare-earth ions. The only exceptions are associated with the apex oxygen O(1) ions: the chain copper Cu(1)-O(1) distances are constant within error limits, and the plane copper Cu(2)-O(1) distances are increasing across the rare-earth series. The much stronger increase of the distance Cu(2)-O(1) in the RBa2Cu3O6 series compared to the RBa2Cu3O7 series can be explained by the increase of Tc from 90 K for YbBa2Cu3O7 to 96 K for NbBa2Cu3O7. The smaller distance Cu(1)-O(1) for the RBa2Cu3O6 series compared to the RBa2Cu3O7 series may be related to the suggested double-well potential of the apical oxygen ion. For some interionic distances of PrBa2Cu3O7 approximately parallel to the h direction (i.e., the chain direction) we determine by extrapolation a valence of +3.4 for the Pr ions. This indicates for PrBa2Cu3O7 a highly anisotropic 4f-CuO2 valence band hybridization. An important structural property with respect to the superconductivity is the puckering of the CuO2 planes: the superconductivity is lost when the puckering angle exceeds a critical value of about 167.3.

Formation of a magnetic soliton lattice in copper metaborate.

The magnetic ground state of CuB2O4 is incommensurate at T = 1.8 K and undergoes a continuous phase transition to a noncollinear commensurate antiferromagnetic state at T(small star), filled approximately 10 K. Close to T(small star), filled higher-order magnetic satellites are observed. Coexistence of long- and short-range magnetic order is observed in both magnetic phases. This suggests that the association of the Dzyaloshinskii-Moriya interaction and anisotropy leads to the formation of a magnetic soliton lattice.

Tuning the superconducting and magnetic properties of Fe y Se 0.25 Te 0.75 by varying the iron content

The superconducting and magnetic properties of FeySe0.25Te0.75 single crystals (0.9≤y≤1.1) were studied by means of x-ray diffraction, superconducting quantum interference device magnetometry, muon-spin rotation, and elastic neutron diffraction. The samples with y<1 exhibit coexistence of bulk superconductivity and incommensurate magnetism. The magnetic order remains incommensurate for y≥1 but with increasing Fe content superconductivity is suppressed and the magnetic correlation length increases. The results show that the superconducting and the magnetic properties of the FeySe1−xTex can be tuned not only by varying the Se/Te ratio but also by changing the Fe content. ©2010 The American Physical Society

Coexistence of incommensurate magnetism and superconductivity in Fe 1 + y Se x Te 1 − x

We have studied the superconducting and magnetic properties of

Spin Waves and Magnetic Interactions in LiCu2O2

{\text{Fe}}_{1+y}{\text{Se}}_{x}{\text{Te}}_{1\ensuremath{-}x}

Damping of Spin Waves and Singularity of the Longitudinal Modes in the Dipolar Critical Regime of the Heisenberg-Ferromagnet EuS

single crystals

Simultaneous antiferromagnetic Fe3+ and Nd3+ ordering in NdFe3(11BO3)4

(0\ensuremath{\le}x\ensuremath{\le}0.5)

Single magnetic chirality in the magnetoelectric NdFe3(11BO3)4

by magnetic susceptibility, muon-spin rotation, and neutron diffraction. We find three regimes of behavior: (i) commensurate magnetic order for

Spin-glass state and long-range magnetic order in Pb ( Fe 1 / 2 Nb 1 / 2 ) O 3 seen via neutron scattering and muon spin rotation

x\ensuremath{\lesssim}0.1