Andrew Sazonov

Development of compact magnetostatic cavities for 3He spin filter cells

In order to preserve the 3He polarization in a spin filter cell used as a polarizer or analyser on a neutron beam line, the cell should be situated in a homogeneous magnetic guide field. Mu-metal magnetic shields are used to assure the stability of the guide field in the presence of moderate magnetic stray fields. Very compact (shoe box dimension) magnetostatic cavities made of mu-metal and permanent magnets have recently been constructed and optimized for rather large (13 cm long, 6 cm diameter) spin filter cells for use with hot neutrons. The relaxation time due to the magnetic gradients measured in the cells, situated in these compact boxes, is more than 500 h at 1 bar 3He pressure. Here we present the construction of such cavities and discuss the possibilities of further improvement in performance.

The low-temperature crystal structure of the multiferroic melilite Ca2CoSi2O7.

In the antiferromagnetic ground state, below TN ≃ 5.7 K, Ca2CoSi2O7 exhibits strong magnetoelectric coupling. For a symmetry-consistent theoretical description of this multiferroic phase, precise knowledge of its crystal structure is a prerequisite. Here we report the results of single-crystal neutron diffraction on Ca2CoSi2O7 at temperatures between 10 and 250 K. The low-temperature structure at 10 K was refined assuming twinning in the orthorhombic space group P2(1)2(1)2 with a 3 × 3 × 1 supercell [a = 23.52 (1), b = 23.52 (1), c = 5.030 (3) Å] compared with the high-temperature normal state [tetragonal space group P42(1)m, a = b ≃ 7.86, c ≃ 5.03 Å]. The precise structural parameters of Ca2CoSi2O7 at 10 K are presented and compared with the literature X-ray diffraction results at 130 and 170 K (low-temperature commensurate phase), as well as at ∼ 500 K (high-temperature normal phase).

Double-layered monopolar order in the Tb2Ti2O7spin liquid

Ho2Ti2O7 and Dy2Ti2O7 spin ices exhibit elementary excitations akin to magnetic monopoles. Here we focus on Tb2Ti2O7 spin liquid, where correlated magnetic moments keep fluctuating down to very low temperatures. Using a monopole picture, we have re-analyzed the field-induced magnetic structure previously determined by neutron diffraction in Tb2Ti2O7. We show that under a high field applied along a [110] direction, Tb2Ti2O7 orders as a three dimensional arrangement of monopole and antimonopole double layers. In contrast, Ho2Ti2O7 spin ice in the same conditions behaves as a monopole-free state. By symmetry analysis we derived the distortions compatible with the observed magnetic structure of Tb2Ti2O7 which can be related to the appearance of the double-layered monopolar order.

Low temperature magnetic structure of CeRhIn5 by neutron diffraction on absorption-optimized samples

Two aspects of the ambient pressure magnetic structure of heavy fermion material CeRhIn5 have remained under some debate since its discovery: whether the structure is indeed an incommensurate helix or a spin density wave, and what is the precise magnitude of the ordered magnetic moment. By using a single crystal sample optimized for hot neutrons to minimize neutron absorption by Rh and In, here we report an ordered moment of [Formula: see text]. In addition, by using spherical neutron polarimetry measurements on a similar single crystal sample, we have confirmed the helical nature of the magnetic structure, and identified a single chiral domain.

Implementation of a new Cryopad on the diffractometer POLI at MLZ

A new polarized neutron single crystal diffractometer POLI (Polarization Investigator) has been developed at the Maier-Leibnitz Zentrum, Garching, Germany. After reviewing existing devices, spherical neutron polarimetry has been implemented on POLI as a main experimental technique using a third-generation cryogenic polarization analysis device (Cryopad) built in cooperation between RWTH University and Institut Laue-Langevin. In this report we describe the realization and present the performance of the new Cryopad on POLI. Some improvements in the construction as well as details regarding calibrations of Cryopad and its practical use are discussed. The reliable operation of the new Cryopad on POLI is also demonstrated.

Origin of forbidden reflections in multiferroic Ba2CoGe2O7 by neutron diffraction: Symmetry lowering or Renninger effect?

For a symmetry consistent theoretical description of the multiferroic phase of Ba

Tunable emergent heterostructures in a prototypical correlated metal

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Crystal Structure of Magnetoelectric Ba2MnGe2O7 at Room and Low Temperatures by Neutron Diffraction

CoGe

Spherical neutron polarimetry in multiferroics under external stimuli

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Neutron diffraction study and magnetic properties of La1−xBaxCoO3 (x = 0.2 and 0.3)

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