arXiv subjects

D. Sheptyakov

Publications and source records attributed to D. Sheptyakov.

20 records · Page 2Linked to original sources

arXiv2006

Simultaneous Antiferromagnetic Fe3+ and Nd3+ Ordering in NdFe3(11BO3)4

By means of magnetic susceptibility and specific heat measurements, x-ray and unpolarised neutron diffraction investigations on powder and single-crystal samples, simultaneous long-range antiferromagnetic Fe and Nd ordering in NdFe3(11BO3)4 with R 3 2 chemical structure has been found at temperatures below TN = 30.5(5) K down to 1.6 K. At temperatures down to 20 K to the propagation vector is khex = [0,0,3/2] and becomes slightly incommensurate at lower temperatures. Symmetry analysis yields magnetic spiral configurations with the magnetic moments oriented parallel to hexagonal basal plane according to the irreducible representations tau_3 in the commensurate case. This is in agreement with the easy directions of magnetisation perpendicular to the c-axis as determined by magnetic susceptibility measurements. At 1.6 K the magnetic Fe moment amounts to 4.9 muB close to the free ion moment of Fe3+. The magnetic Nd3+ moment saturates presumably due to crystal-field effects at 2.7 muB.

cond-mat.mtrl-sci↗

arXiv2004

Neutron scattering study of PbMg$_{1/3}$Ta$_{2/3}$O$_3$ and BaMg$_{1/3}$Ta$_{2/3}$O$_3$ complex perovskites

Neutron scattering investigations were carried out in PbMg$_{1/3}$Ta$_{2/3}$O$_3$ and BaMg$_{1/3}$Ta$_{2/3}$O$_3$ complex perovskites. The crystal structure of both compounds does not show any phase transition in the temperature range 1.5 -- 730 K. Whereas the temperature dependence of the lattice parameter of BaMg$_{1/3}$Ta$_{2/3}$O$_3$ follows the classical expectations, the lattice parameter of relaxor ferroelectric PbMg$_{1/3}$Ta$_{2/3}$O$_3$ exhibits anomalies. One of these anomalies is observed in the same temperature range as the peak in the dielectric susceptibility. We find that in PbMg$_{1/3}$Ta$_{2/3}$O$_3$, lead ions are displaced from the ideal positions in the perovskite structure at all temperatures. Consequently short-range order is present. This induces strong diffuse scattering with an anisotropic shape in wavevector space. The temperature dependences of the diffuse neutron scattering intensity and of the amplitude of the lead displacements are similar.

cond-mat.mtrl-sci↗