SANS polarization analysis at V4 SANS instrument of HMI Berlin

Abstract

The V4 instrument has recently been upgraded with a 3 He spin filter cell, placed directly in the homogeneous field B of the sample magnet, to enhance the SANSPOL option for polarization analysis. The prototype setup was still affected by: (a) a quick relaxation of the 3 He nuclear polarization in the cell with a time constant of only ≈130 min which significantly changes the spin filter transmissions T + and T − for neutrons polarized parallel I + and anti-parallel I − to B, and (b) the absence of a flipping aid behind the sample. The usual polarization analysis procedure, expecting virtually time-independent transmissions and a second flipping device, is therefore not applicable. We present an alternative way of polarization analysis, developed especially for this case of a spin filter cell with insufficient time stability, and not requiring a second flipper. A concentrated Co-ferrofluid sample 'MFT3N' was measured with the spin filter cell for 5.5 h. From the time-dependent change of I + and I − caused by the change of T + and T − , the spin-flip and non-spin-flip components of the scattering were calculated by fitting procedures. The two-dimensional flip patterns obtained represent the purely magnetic scattering contribution, featuring the typical (sin α cos α) 2 angular behavior expected for superparamagnetic systems.

Neutron spin-flip scattering of nanocrystalline cobalt

“…The scattered neutrons were detected by a multi-tube detector which consists of 128 pixels × 128 pixels (resolution: 8 mm × 8 mm). Rawdata treatment was carried out by means of the GRASP [18] and BerSANS [14,19] software packages. Due to the limited beamtime and in the interest of exploring a maximum range within the experimental parameter space, we have not performed a so-called spin-leakage correction.…”

PolarizedHe3as a Probe for Short-Range Spin-Dependent Interactions

“…They include magnetic resonance imaging, spin-polarized targets, surface science, probing of biological systems, and precision measurements in fundamental physics [1][2][3][4][5][6][7][8][9][10]. One of the unique properties of polarized 3 He is the very long spinrelaxation time constant which can be of the order of thousands of hours [11,12], making polarized 3 He extremely sensitive to any spin-dependent interaction.…”

Relaxation mechanisms in magnetic colloids studied by stroboscopic spin-polarized small-angle neutron scattering

“…The samples sealed in quartz containers were cooled down in a closed cycle refrigerator to 20 K. Standard cell-by-cell data corrections and regrouping of time-dependent data have been performed by the software package BerSANS. 20 Instead of analyzing the full 3D intensity pattern I (Q, ψ, t), we first integrated the intensity over a restricted Q-range region of interest (ROI) ( Q, ψ), which have been chosen to cover the interparticle correlation peaks known from previous SANS investigations. [12][13][14] The time dependence of different ROIs has been analyzed in terms of Eq.…”