Triangular lattice magnet GdGa${}_2$ with short-period spin cycloids and possible skyrmion phases

Abstract

The two-dimensional triangular lattice (TAL) is a model system of magnetic frustration and competing interactions, where skyrmion spin vortices can be induced by a vertical magnetic field $B$. We target the binary compound GdGa${}_2$ with an undistorted TAL of Gd${}^{3+}$ Heisenberg moments. At higher temperature ($T>5$ K, $B=0$, phase II), we reveal the cycloidal spin textures in GdGa${}_2$ via resonant elastic X-ray scattering (REXS). Further, a transition with strong magneto-elastic response occurs when cooling into the zero-field ground state ($T<5$ K, phase I). We also report the thermodynamic phase boundaries of $B$-induced magnetic A-phases, which are suppressed by an in-plane magnetic field and which have enhanced resistivity due to the partial opening of a charge gap. In analogy to Gd${}_2$PdSi${}_3$ and GdRu${}_2$Si${}_2$, these phases may represent a superposition of various cycloids, possibly a Néel skyrmion lattice. Our work lays the basis for further studies of the magnetic phase diagram of GdGa${}_2$.

19 pages, 9 figures