Competition between magnetic interactions and structural instabilities leading to itinerant frustration in the triangular lattice antiferromagnet LiCrSe2
Elisabetta Nocerino, Shintaro Kobayashi, Catherine Witteveen, Ola Kenji Forslund, Nami Matsubara, Chiu C. Tang, Takeshi Matsukawa, Akinori Hoshikawa, A. Koda, Kazuyoshi Yoshimura, Izumi Umegaki, Yasmine Sassa, Fabian O. von Rohr, Vladimir Pomjakushin, J. H. Brewer, Jun Sugiyama, Martin Må̊nsson
Abstract
Abstract LiCrSe 2 constitutes a recent valuable addition to the ensemble of two-dimensional triangular lattice antiferromagnets. In this work, we present a comprehensive study of the low temperature nuclear and magnetic structure established in this material. Being subject to a strong magnetoelastic coupling, LiCrSe 2 was found to undergo a first order structural transition from a trigonal crystal system ( $$P\bar{3}m1$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mi>P</mml:mi> <mml:mover> <mml:mrow> <mml:mn>3</mml:mn> </mml:mrow> <mml:mo>¯</mml:mo> </mml:mover> <mml:mi>m</mml:mi> <mml:mn>1</mml:mn> </mml:math> ) to a monoclinic one ( C 2/ m ) at T s = 30 K. Such restructuring of the lattice is accompanied by a magnetic transition at T N = 30 K. Refinement of the magnetic structure with neutron diffraction data and complementary muon spin rotation analysis reveal the presence of a complex incommensurate magnetic structure with a up-up-down-down arrangement of the chromium moments with ferromagnetic double chains coupled antiferromagnetically. The spin axial vector is also modulated both in direction and modulus, resulting in a spin density wave-like order with periodic suppression of the chromium moment along the chains. This behavior is believed to appear as a result of strong competition between direct exchange antiferromagnetic and superexchange ferromagnetic couplings established between both nearest neighbor and next nearest neighbor Cr 3+ ions. We finally conjecture that the resulting magnetic order is stabilized via subtle vacancy/charge order within the lithium layers, potentially causing a mix of two co-existing magnetic phases within the sample.