Complex magnetic structure of a new pressure-induced Kondo lattice superconductor

In unconventional superconductors such as heavy fermion and high-Tc superconductors, superconductivity is believed to be mediated by spin fluctuations, rather than the electron-phonon pairing mechanism of BCS theory. However, the microscopic mechanisms of spin-fluctuation mediated superconductivity are not yet determined, and it is important to understand the nature of the magnetism that occurs in close proximity to unconventional superconductivity. We propose to use single-crystal neutron diffraction to determine the magnetic structure of CeSb2 at ambient pressure. CeSb2 orders antiferromagnetically at ambient pressure, and was recently found to exhibit superconductivity under pressure upon the suppression of antiferromagnetism, with highly unusual behaviour of the upper critical field. Previous neutron scattering measurements show complex magnetic ordering in CeSb2 with three magnetic transitions, where there are multiple magnetic propagation vectors but the magnetic structures are not determined. We will perform detailed neutron diffraction measurements in three magnetic phases using the SXD instrument, so as to collect the intensity of the magnetic Bragg reflections, and determine the magnetic structures. These results will provide important information for understanding the magnetic exchange interactions, which give rise to both the ordered magnetic state at ambient pressure, and the unconventional, possibly spin-triplet, heavy fermion superconductivity under pressure.