Noncollinear magnetic order in epitaxial thin films of the centrosymmetric MnPtGa hard magnet

Abstract

Magnetic systems exhibiting spin-canted states have garnered much attention recently for their promising rich exotic properties driven by the real-space spin textures and competing magnetic orders. In this study, we present the structural and magnetic properties of hexagonal 60 nm MnPtGa epitaxial thin films grown by magnetron sputtering on Al2O3(0001) single-crystalline substrates. The MnPtGa film crystallizes in the centrosymmetric P63/ mmc (No. 194) space group, showing perpendicular magnetic anisotropy along the c-axis, with a Curie temperature TC = 263 K. In addition, the MnPtGa film undergoes a spin reorientation transition at Tsr = 160 K. We investigated the MnPtGa magnetic ground states using single-crystal neutron diffraction. A structurally forbidden (001) magnetic Bragg reflection emerges below Tsr, indicating the existence of a spin-canted state, where the magnetic moments align ferromagnetically perpendicular to the basal plane, and a non-zero in-plane component exhibits an antiferromagnetic ordering along the c-axis. At 2 K, the refined magnetic moments of Mn are μz = 4.2(4) μB and μx = 1.5(3) μB, projected onto the c-axis and basal plane, respectively. Hence, we determined a 20° Mn spin canting angle off from the c-axis.

Anomalous Hall Effect in Epitaxial Thin Films of the Hexagonal Heusler MnPtGa Noncollinear Hard Magnet

“…Figure 1a shows the primitive unit cell of hexagonal MnPtGa crystal, together with the noncollinear magnetic structure formed by Mn spins. [ 6 ] Resorting to single‐crystal neutron diffraction, on a nominally identical 60 nm thick (0001)‐Al 2 O 3 /MnPtGa film, we found that in zero external magnetic fields, the magnetic ground state of the system is composed of ferromagnetically aligned Mn‐spins in the basal plane, with an in‐plane (IP) moment component ordering antiferromagnetically along the [0001] out‐of‐plane direction. Together with the magnetocrystalline anisotropy, these competing exchange interactions set a global staggered spin‐canted state, where the Mn‐spins are found to tilt 20 o away from the c ‐axis.…”

“…Together with the magnetocrystalline anisotropy, these competing exchange interactions set a global staggered spin‐canted state, where the Mn‐spins are found to tilt 20 o away from the c ‐axis. [ 6 ]…”

“…First Principle Calculations: The electronic structure calculations were performed using the full-potential linearized augmented plane wave method implemented in Fleur code [57] within the generalized gradient approximation (GGA). [58] The crystal structure and parameters were set according to the experimentally determined values at 2 K. [6] The total energy of the self-consistent calculations converged to less than 0.1 meV with a plane-wave cutoff of 3.9 a.u. −1 , and a k-point mesh of (26 × 26 × 18).…”

“…We build upon a previous experimental work, where we investigated the magnetic ground state (a noncollinear spin‐canted phase) of hexagonal (0001)‐Al 2 O 3 /MnPtGa heteroepitaxial system by single‐crystal neutron diffraction. [ 6 ] We also present first‐principle density functional theory (DFT) calculations of ferromagnetic MnPtGa electronic band structure including SOC, and calculate the corresponding energy‐dependent AHC. We find that the AHC is strongly enhanced at symmetry‐protected band crossings and obtain a semi‐quantitative agreement between the calculated value of the AHC for off‐stoichiometric hexagonal MnPtGa, and the experimentally determined AHC $$\sigma _{{\rm{xy}}}^{{\rm{AH}}}$$ = −154.7 Ω −1 cm −1 at 5 K, for the 60 nm thick film.…”

“…[ 5 ] Recently, we have demonstrated that epitaxial MnPtGa films are found to crystallize in the centrosymmetric hexagonal structure, exhibit PMA, and host a spin‐canted magnetic ground state where the Mn moments tilt 20 o away from the c ‐axis, below T sr (as depicted in Figure a). [ 6 ] While these studies have focused on the magnetic properties and groundstate of MnPtGa compounds, their electrical transport properties have so far remained largely unexplored.…”