The planar triangular $S=3/2$ magnet AgCrSe$_2$: magnetic frustration, short range correlations, and field tuned anisotropic cycloidal magnetic order
cond-mat.str-el
/ Authors
M. Baenitz, M. M. Piva, S. Luther, J. Sichelschmidt, K. M. Ranjith, H. Dawczak-Dȩbicki, M. O. Ajeesh, S. -J. Kim, G. Siemann, C. Bigi
and 18 more authors
P. Manuel, D. Khalyavin, D. A. Sokolov, P. Mokhtari, H. Zhang, H. Yasuoka, P. D. C. King, G. Vinai, V. Polewczyk, P. Torelli, J. Wosnitza, U. Burkhardt, B. Schmidt, H. Rosner, S. Wirth, H. Kühne, M. Nicklas, M. Schmidt
/ Abstract
Our studies evidence an anisotropic magnetic order below $T_N = 32$~K. Susceptibility data in small fields of about 1~T reveal an antiferromagnetic (AFM) order for $H \perp c$, whereas for $H \parallel c$ the data are reminiscent of a field-induced ferromagnetic (FM) structure. At low temperatures and for $H \perp c$, the field-dependent magnetization and AC susceptibility data evidence a metamagnetic transition at $H^+ = 5$~T, which is absent for $H \parallel c$. We assign this to a transition from a planar cycloidal spin structure at low fields to a planar fan-like arrangement above $H^+$. A fully FM polarized state is obtained above the saturation field of $H_{\perp S} = 23.7$~T at 2~K with a magnetization of $M_s = 2.8$~$μ_{\rm B}{\rm /Cr}$. For $H \parallel c$, $M(H)$ monotonously increases and saturates at the same $M_s$ value at $H_{\parallel S} = 25.1$~T at 4.2~K. Above $T_N $, the magnetic susceptibility and specific heat indicate signatures of two dimensional (2D) frustration related to the presence of planar ferromagnetic and antiferromagnetic exchange interactions. We found a pronounced nearly isotropic maximum in both properties at about $T^* = 45$~K, which is a clear fingerprint of short-range correlations and emergent spin fluctuations. Calculations based on a planar 2D Heisenberg model support our experimental findings and suggest a predominant FM exchange among nearest and AFM exchange among third-nearest neighbors. Only a minor contribution might be assigned to the antisymmetric Dzyaloshinskii-Moriya interaction possible related to the non-centrosymmetric polar space group $R3m$. Due to these competing interactions, the magnetism in AgCrSe$_{2}$, in contrast to the oxygen based delafossites, can be tuned by relatively small, experimentally accessible, magnetic fields, allowing us to establish the complete anisotropic magnetic $H-T$ phase diagram in detail.