Non-oxy delafossite magnet AgCrSe2: Magnetic frustration, short range correlations, and field-tuned anisotropic cycloidal magnetic order

Abstract:

In contrast to Cr-based oxy delafossites with predominant antiferromagnetic (afm) nearest neighbor interaction in the planar Heisenberg triangular lattice, AgCrSe₂ as a representative of the non-oxy delafosites is characterized by competing interactions (ferromagnetic nearest-neighbor vs afm third-neighbor interactions). Due to these competing interactions, the magnetism in AgCrSe₂ can be tuned by relatively small, experimentally accessible magnetic fields, allowing us to establish the complete anisotropic magnetic H-T phase diagram in great detail. So far, there are only a few single-crystal studies of Cr-based non-oxy (S,Se,Te) delafossites. We were able to successfully grow large AgCrSe₂ single crystals by chemical vapor transport at the MPI-CPfS. The crystals have been carefully characterized and studied by magnetic susceptibility, magnetization, specific heat, and thermal expansion. In addition, we used Cr-electron spin resonance and neutron diffraction to probe the Cr 3d³ magnetism microscopically. Our studies evidence an anisotropic magnetic order below TN = 32 K. Studies in collaboration with the Rossendorf High Field Laboratory and the ISIS Neutron and Muon Facility (Oxford, UK) demonstrate anisotropic cycloidal magnetic ordering with unusual extended two-dimensional fluctuations [1]. Previously unpublished magnetization measurements below 1 T indicate the presence of domains which may have a chiral spin texture. This would also explain the unconventional anomalous Hall effect. In contrast to the oxy delafossites (with R-3m space group), the non-oxy delafossites have a reduced symmetry space group (R3m) which allows antisymmetric interactions (Dzyaloshinskii-Moriya). Possibly this plays a role in small fields. In this respect, small-angle neutron-scattering experiments (SANS) in small magnetic fields are of particular interest in the future.

M. Baenitz et al. Phys. Rev. B 104, 134410 (2021)

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