Neutron depolarization imaging of the hydrostatic pressure dependence of inhomogeneous ferromagnets

Abstract

The investigation of fragile and potentially inhomogeneous forms of ferromagnetic order under extreme conditions, such as low temperatures and high pressures, is of central interest for areas such as geophysics, correlated electron systems, as well as the optimization of materials synthesis for applications where particular material properties are required. We report neutron depolarization imaging measurements on the weak ferromagnet Ni 3 Al under pressures up to 10 kbar using a Cu:Be clamp cell. Using a polychromatic neutron beam with wavelengths λ ≥ 4Å in combination with3 He neutron spin filter cells as polarizer and analyzer we were able to track differences of the pressure response in inhomogeneous samples by virtue of high resolution neutron depolarization imaging. This provides spatially resolved and non-destructive access to the pressure dependence of the magnetic properties of inhomogeneous ferromagnetic materials.

Setup for polarized neutron imaging using in situ 3He cells at the Oak Ridge National Laboratory High Flux Isotope Reactor CG-1D beamline

“…As a result, no change in the transmission value is expected, reaching a plateau. The advantage of the polychromatic neutron beam towards the qualitative understanding of magnetic phase transitions has been reported by Schulz et al 11 It is interesting to point out that the periodicity of the transmission curves is different for the polychromatic and monochromatic measurements ( Fig. 4).…”

“…Neutrons have spin and thus are sensitive to the magnetic field distribution in and around the sample, such as in superconducting and ferromagnetic materials. [1][2][3][4][5][6][7][8][9][10][11][12] Polarized neutrons passing through an inhomogeneous magnetic field experience different Larmor precessions, dependent on the magnetic field strength and path integral through the sample. This path-dependent neutron spin rotation can be analyzed by a neutron spin analyzer placed after the sample.…”

A Neutron Depolarization Measurement of Single Crystal Fe by Using a 3He Neutron Spin Filter and Magnetic Super-mirrors

“…where P N0 is initial neutron polarization degree,  = 1.83 x 10 8 s -1 T -1 the gyromagnetic ratio of the neutron, B magnitude of the magnetic field of a magnetic domain, d a thickness of the volume,  an average domain size, and v a neuron velocity [10].…”

High-resolution neutron depolarization microscopy of the ferromagnetic transitions in Ni3Al and HgCr2Se4 under pressure

“…Neutron depolarization imaging (NDI) provides a spatially-resolved thermodynamic probe of a sample's magnetic state [26,27], and potentially a three-dimensional distribution of the magnetic field [28,29,30,31]. Neutrons readily penetrate cryogenic equipment, pressure cells and bulk metal samples.…”