Abstract
Single crystals of the hexagonal triangular lattice compound AgCrSe2 have been grown by chemical vapor transport. 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. To obtain the electronic density of states, we employed x-ray absorption and resonant photoemission spectroscopy in combination with density functional theory calculations. Our studies evidence an anisotropic magnetic order below TN=32K. Susceptibility data in small fields of about 1 T reveal an antiferromagnetic (AFM) type of order for H⊥c, whereas for H∥c the data are reminiscent of a field-induced ferromagnetic (FM) structure. At low temperatures and for H⊥c, the field-dependent magnetization and AC susceptibility data evidence a metamagnetic transition at H+=5T, which is absent for H∥c. We assign this to a transition from a planar cycloidal spin structure at low fields to a planar fanlike arrangement above H+. A fully ferromagnetically polarized state is obtained above the saturation field of H⊥S=23.7T at 2 K with a magnetization of Ms=2.8μB/Cr. For H∥c, M(H) monotonically increases and saturates at the same Ms value at H∥S=25.1T at 4.2 K. Above TN, 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*=45K, 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 possibly related to the noncentrosymmetric polar space group R3m. Due to these competing interactions, the magnetism in AgCrSe2, 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.9 MoreReceived 4 August 2021Revised 3 September 2021Accepted 20 September 2021DOI:https://doi.org/10.1103/PhysRevB.104.134410Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI. Open access publication funded by the Max Planck Society.Published by the American Physical SocietyPhysics Subject Headings (PhySH)Research AreasFrustrated magnetismMagnetic susceptibilityThermal expansionTechniquesElectron spin resonanceNeutron diffractionPhotoemission spectroscopySpecific heat measurementsCondensed Matter & Materials Physics
Highlights
Whereas the magnetism in chromium oxygen-based delafossites, e.g., CuCrO2, is quite robust against applied magnetic fields and no saturation of the magnetization occurs up to 100 T [31], we show that the magnetism of AgCrSe2 can be tuned to saturation by magnetic fields in the range of a few tens of teslas and that the expected saturation magnetization for S = 3/2 Cr3+ close to 3 μB/Cr is obtained
In a first step polycrystalline AgCrSe2 material has been synthesized by a direct reaction of the elements silver, chromium, and selenium at 800 ◦C
Selected crystals were characterized by energydispersive x-ray spectroscopy (EDXS), wavelength-dispersive x-ray spectroscopy (WDXS), x-ray powder diffraction, Laue x-ray diffraction, and differential scanning calorimetry (DSC)
Summary
Bonded two dimensional (2D) structures are frequently found with the triangular motif realized by a simple planar hexagonal lattice, in particular, and by more. Anisotropic metallic conductivity due to anisotropic hybridization of electronic states evolves through a bonding situation given by the crystal structure. The simplest examples are graphite and graphene crystallizing in a hexagonal and a honeycomb lattice, respectively. The latter exhibits very intriguing properties, such as high charge carrier mobility due to the formation of Dirac nodes near the Fermi level in the electronic band structure [1]. The triangular lattice delafossite PdCoO2 belongs to the latter material class, which is characterized by an unusually high in-plane charge carrier mobility [3,4].
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