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

Pau Jorba; Michael Schulz; Daniel S Hussey; Muhammad Abir; Marc Seifert; Vladimir Tsurkan; Alois Loidl; Christian Pfleiderer; Boris Khaykovich

doi:10.1016/j.jmmm.2018.11.086

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

J Magn Magn Mater. 2019:475:10.1016/j.jmmm.2018.11.086. doi: 10.1016/j.jmmm.2018.11.086.

Authors

Pau Jorba¹, Michael Schulz², Daniel S Hussey³, Muhammad Abir⁴, Marc Seifert^{1

2}, Vladimir Tsurkan^{5

6}, Alois Loidl⁵, Christian Pfleiderer¹, Boris Khaykovich⁴

Affiliations

¹ Physik-Department, Technische Universität München, D-85748 Garching, Germany.
² Heinz-Maier-Leibnitz Zentrum (MLZ), Technische Universität München, D-85748 Garching, Germany.
³ Physical Measurement Laboratory, National Institute of Standards and Technology, 100 Bureau Drive, MS 8461, Gaithersburg, MD 20899-8461, USA.
⁴ Nuclear Reactor Laboratory, Massachusetts Institute of Technology, 77 Massachusetts Ave., Cambridge, MA, USA.
⁵ Experimental Physics V, Center for Electronic Correlations and Magnetism, University of Augsburg, D-86159 Augsburg, Germany.
⁶ Institute of Applied Physics, Chisinau, Republic of Moldova.

Abstract

We performed neutron imaging of ferromagnetic transitions in Ni₃Al and HgCr₂Se₄ crystals. These neutron depolarization measurements revealed bulk magnetic inhomogeneities in the ferromagnetic transition temperature with spatial resolution of about 100 μm. To obtain such spatial resolution, we employed a novel neutron microscope equipped with Wolter mirrors as a neutron image-forming lens and a focusing neutron guide as a neutron condenser lens. The images of Ni₃Al show that the sample does not homogeneously go through the ferromagnetic transition; the improved resolution allowed us to identify a distribution of small grains with slightly off-stoichiometric composition. Additionally, neutron depolarization imaging experiments on the chrome spinel, HgCr₂Se₄, under pressures up to 15 kbar highlight the advantages of the new technique especially for small samples or sample environments with restricted sample space. The improved spatial resolution enables one to observe domain formation in the sample while decreasing the acquisition time despite having a bulky pressure cell in the beam.

Keywords: Crystal growth; Magnetic domains; Magnetic phase transitions; Neutron imaging; Pressure techniques; Quantum phase transitions.

Grants and funding

9999-NIST/ImNIST/Intramural NIST DOC/United States