New high field magnet for neutron scattering at Hahn Meitner Institute

Abstract The Berlin Neutron Scattering Center BENSC at the Hahn Meitner Institute HMI is a user facility for the study of structure and dynamics of condensed matter with neutrons and synchrotron radiation with special emphasis on experiments under extreme conditions. Neutron scattering is uniquely suited to study magnetic properties on a microscopic length scale, because neutrons have comparable wavelengths and, due to their magnetic moment, they interact with the atomic magnetic moments. Magnetic interactions and magnetic phenomena depend on thermodynamic parameters like magnetic field, temperature and pressure. At HMI special efforts are being made to offer outstanding sample environments such as very low temperatures or high magnetic fields or combination of both. For the future a dedicated instrument for neutron scattering at extreme fields is under construction, the Extreme Environment Diffractometer ExED. For this instrument the existing superconducting magnets as well as a future hybrid system can be used. The highest fields, above 30 T will be produced by the planned series connected hybrid magnet system, designed and constructed in collaboration with the National High Magnetic Field Laboratory, Tallahassee, F

Field-induced transition between magnetically disordered and ordered phases in underdoped La(2-x)SrxCuO4

We report the observation of a magnetic-field-induced transition between magnetically disordered and ordered phases in slightly under-doped La(2-x)SrxCuO4 with x=0.144. Static incommensurate spin-density-wave order is induced above a critical field of about 3 T, as measured by elastic neutron scattering. Our results allow us to constrain the location of a quantum critical point on the phase diagram.Comment: 10 pages, 2 figures; discussion on the location of a quantum critical point is revise

Final Assembly of the Helmholtz Zentrum Berlin Series Connected Hybrid Magnet System

The final assembly of the Series Connected Hybrid magnet system for the Helmholtz Zentrum Berlin for Materials and Energy HZB has occurred with the integration of the superconducting cold mass, cryostat, resistive Florida Bitter coils, and the cryogenic, chilled water, power, and control subsystems. The hybrid magnet consists of a 13 T superconducting Nb3Sn CICC coil and a set of 12 T resistive, water cooled coils at 4.4 MW. Much of the cryostat and cold mass functional requirements were dictated by the electromagnetic interactions between the superconducting and resistive coils. This includes the radial decentering and axial aligning forces from normal operations and a 1.1 MN fault load. The system assembly was an international achievement with the cold mass being completed at the NHMFL in the USA, cryostat to cold mass interfaces made at Criotec Impianti in Italy, and final assembly at the HZB in German

Noncollinear magnetic structure in U2Pd2In at high magnetic fields

We report an unexpected magnetic field driven magnetic structure in the 5f electron Shastry Sutherland system U2Pd2In. This phase develops at low temperatures from a noncollinear antiferromagnetic ground state above the critical field of 25.8 T applied along the a axis. All U moments have a net magnetic moment in the direction of the applied field, described by a ferromagnetic propagation vector qF 000 and an antiferromagnetic component described by a propagation vector qAF 0 0.3012 due to a modulation in the direction perpendicular to the applied field. We conclude that this surprising noncollinear magnetic structure is due to a competition between the single ion anisotropy trying to keep moments, similar to the ground state, along the [110] type directions, Dzyaloshinskii Moryia interaction forcing them to be perpendicular to each other and application of the external magnetic field attempting to align them along the field directio

Analysis of time of flight small angle neutron scattering data on mesoscopic crystals such as magnetic vortex lattices

Bragg diffracted intensities and q values for crystalline structures with long repeat distances may be obtained by small angle neutron scattering SANS investigations. An account is given of the methods, advantages and disadvantages of obtaining such data by the multichromatic time of flight method, compared with the more traditional quasi monochromatic SANS method. This is illustrated with data obtained from high magnetic field measurements on magnetic vortex line lattices in superconductors on the former HFM EXED instrument at Helmholtz Zentrum Berlin. The methods have application to other mesoscopic crystalline structures investigated by SANS instruments at pulsed source

First Hybrid Magnet for Neutron Scattering at Helmholtz Zentrum Berlin

Helmholtz Zentrum Berlin HZB operates two large scale facilities the research reactor BER 2 and the syn chrotron source for soft X rays BESSY 2. This year HZB s neu tron instrument suite around BER 2 has been strengthened by a unique high magnetic field facility for neutron scattering. Its main components are the High Field Magnet HFM , which is the most powerful dc magnet for neutron scattering worldwide, and the Extreme Environment Di ffractometer EXED , which is a dedicated neutron instrument for time of flight technique. The hybrid magnet system is projected according to the special geo metric constraints of analyzing samples by neutron scattering in a high field magnet. Following our past experience, only steady state fields are adequate to achieve the goals of the project. In particular, inelastic scattering studies would virtually be excluded when using pulsed magnets. The new series connected hybrid magnet with a horizontal field orientation was designed and constructed in collaboration with the National High Magnetic Field Laboratory NHMFL , Tallahassee, FL, USA. With a set consisting of a su perconducting cable in conduit coil and different resistive coils of conical shape, maximum fields between 26 31 T are possible with cooling power between 4 and 8 MW for the resistive part. A series of commissioning activities of the magnet components and the technical infrastructure systems 20 kA power supply, water cooling, and 4 K Helium refrigerator was completed at HZB. The maximum field achieved with a 4 MW resistive coil was 26

Order to disorder transition in the XY-like quantum magnet Cs2CoCl4 induced by noncommuting applied fields

We explore the effects of noncommuting applied fields on the ground-state ordering of the quasi-one-dimensional spin-1/2 XY-like antiferromagnet Cs2CoCl4 using single-crystal neutron diffraction. In zero field interchain couplings cause long-range order below T_N=217(5) mK with chains ordered antiferromagnetically along their length and moments confined to the (b,c) plane. Magnetic fields applied at an angle to the XY planes are found to initially stabilize the order by promoting a spin-flop phase with an increased perpendicular antiferromagnetic moment. In higher fields the antiferromagnetic order becomes unstable and a transition occurs to a phase with no long-range order in the (b,c) plane, proposed to be a spin liquid phase that arises when the quantum fluctuations induced by the noncommuting field become strong enough to overcome ordering tendencies. Magnetization measurements confirm that saturation occurs at much higher fields and that the proposed spin-liquid state exists in the region 2.10 < H_SL < 2.52 T || a. The observed phase diagram is discussed in terms of known results on XY-like chains in coexisting longitudinal and transverse fields.Comment: revtex, 14 figures, 2 tables, to appear in Phys. Rev.

Excitations of the field-induced soliton lattice in CuGeO3

Here we report the first inelastic neutron scattering study of the magnetic excitations in the incommensurate phase of a spin-Peierls material. The results on CuGeO3 provide direct evidence of a finite excitation gap, two sharp magnetic excitation branches and a very low-lying excitation which is identified as a phason mode, the Goldstone mode of the incommensurate soliton lattice.Comment: 5 pages, revtex, 4 figures (*.eps), win-zippe

HFM EXED The High Magnetic Field Facility for Neutron Scattering at BER II

An overview of the high magnetic field facility for neutron scattering at Helmholtz Zentrum Berlin HZB is given. The facility enables elastic and inelastic neutron scattering experiments in continuous magnetic fields up to 26.3 T combined with temperatures down to 0.6