[Seminar] Dr. Gøran Nilsen "Collinear spin nematic phase in a breathing pyrochlore spinel "

Speaker

Dr. Gøran Nilsen / ISIS Neutron and Muon Source

Title

Collinear spin nematic phase in a breathing pyrochlore spinel

Abstract

The combination of magnetic frustration and strong spin-lattice coupling can lead to a wide variety of novel magneto-structural behaviours. This is exemplified by the breathing pyrochlore spinels LiGa_xIn_1−xCr₄O₈, where the end-member compounds (x = 0 and x = 1) exhibit complex sequences of magnetic and structural phase transitions [1]. Here, we show that replacing 5% Ga with In (x = 0.05) apparently suppresses this complexity, leaving only a single transition. A combination of neutron diffraction and NMR allows us to identify the low-temperature state with a collinear nematic state (also known as antiferromagnetic spin ice) associated with an effective biquadratic spin-lattice coupling term [2]. Reverse Monte Carlo analysis of the diffuse magnetic neutron scattering indicates the presence of both Coulomb-like spin correlations at high temperature, and short-range order between collinear local spin configurations at low temperature. The dynamical structure factor as probed by inelastic neutron scattering reveals a continuum of excitations with a broad maximum at around 6 meV [3]. Landau-Lifshitz spin dynamics simulations combined with linear spin wave theory reveal that the latter may be associated with ferromagnetic loop dynamics lifted to finite energy transfer by the biquadratic term [4].

[1] G. J. Nilsen et al., Phys. Rev. B, 91, 174435, 2015.
[2] R. Wawrzynczak et al., Phys. Rev. Lett., 119, 087201, 2017.
[3] Y. Tanaka et al., J. Phys. Soc. Japan, 87, 073710, 2018.
[4] A. Szabó and G. J. Nilsen, Phys. Rev. B, 109, 104425, 2024.

Profile of Speaker

Gøran Nilsen graduated with a PhD in chemistry from the University of Edinburgh in 2010, then worked in Switzerland (EPFL, U. Bern), Japan (U. Tokyo), and France (ILL), before ending up at the ISIS Neutron and Muon Source in the UK in 2015. At ISIS, he is responsible for the design, construction, and operation of polarized neutron instrumentation across the facility, including the LET time-of-flight spectrometer and the WISH diffractometer. His science mainly focuses on inorganic and metal-organic materials ranging from ionic conductors for energy applications to frustrated and low-dimensional magnets. Although neutron scattering is the central technique used in his research, he occasionally ventures into numerical simulations of materials properties.

Join Zoom link
Meeting ID: 944 3539 5695
Passcode: 246005