Uniaxial stress control of versatile helimagnetic phases in the square-lattice itinerant magnet EuAl$_{4}$

Abstract

We investigate uniaxial-stress effects on the magnetic phase diagram of the square-lattice itinerant magnet EuAl$_{4}$, where strong coupling among spin, lattice, and charge produces a variety of helimagnetic phases, including rhombic and square skyrmion lattices. Combining resistivity and magnetization measurements with neutron scattering, we find that compressive stresses of only several tens of MPa along [010] enhance antiferromagnetic character and shorten the magnetic modulation period in the lowest-temperature single-Q spiral state, thereby driving the critical temperatures and fields of multiple phases to higher values. First-principles calculations show that increasing orthorhombic lattice distortion deforms the Fermi surface relevant to the magnetism, providing compelling evidence that Fermi-surface nesting plays a crucial role in stabilizing the helical magnetic modulations in EuAl$_{4}$.

Figures (4)

• Figure 1: (a) Magnetic-field--stress phase diagram for $H \parallel [001]$ below 5 K, determined from the present magnetization measurements. (b) Temperature--stress phase diagram at zero magnetic field, determined from the present resistivity measurements and neutron-scattering experiments. The compressive uniaxial stress was applied along the [010] direction. (c) Schematic illustration of the magnetic structures and their modulation vectors in the seven helimagnetic phases for $H \parallel [001]$ in EuAl$_{4}$2022_Tak. The helicities in phases I and V are opposite to each other 2024_Mia2024_Vib.
• Figure 2: (a)(b) Schematic illustrations of the experimental geometry for (a) resistivity and (b) magnetization measurements under compressive stress $\sigma_{[010]}$. (c)(d) Temperature dependence of (c) resistivity at 0 T for $I \parallel [100]$ and (d) magnetization at 0.1 T for $H \parallel [001]$ under various stresses. The data were taken during the warming process. In panel (c), each data except for 0 MPa is vertically shifted by 1 $\mu \Omega$ for clarity. (e)(f) Magnetic-field dependence of (e) magnetization and (f) its field derivative at 4 K for $H \parallel [001]$ under various stresses. The data were taken during the field-increasing process. In panel (f), each data except for 0 MPa is vertically shifted for clarity.
• Figure 3: (a) Schematic illustrations of the experimental geometry for neutron scattering experiment under compressive stress $\sigma_{[010]}$. ${\mathbf k}_{i}$ (${\mathbf k}_{f}$) represents the propagation vector of incident (scattered) neutron beam. (b) Correspondence between the orthorhombic distortion and the orientation of the ${\mathbf Q}$ vector in the spiral states of phase I 2023_Gen. (c) Neutron scattering profiles in the $(H, 0, 4)$ scan at $\sigma_{[010]}=0$ (gray) and $\sigma_{[010]}=50$ MPa (red). The data were collected at 2 K in zero magnetic field. (d) Stress dependence of the wavenumber $q$ at 2 K in phase I. (e)--(h) Temperature dependence of $q$ (top) and the integrated intensities of magnetic Bragg peaks (bottom) in phases I (yellow), V (orange), and VI/VII (cyan). The integrated intensities are estimated from Gaussian fits to the observed scattering profiles obtained in the $(H, 0, 4)$ or $(H, H, 4)$ scans, and then normalized to that of the $(q00)$ peak at 2 K.
• Figure 4: (a)(b) Calculated Fermi surfaces (FSs) for band #1 of EuAl$_{4}$, which is relevant to the magnetism. Panel (b) shows the FSs near the Z point within the $k_{x}$--$k_{y}$ plane. Illustrations are drawn by the fermisurfer code 2019_Kaw. (c)(d) Calculated $\sigma_{[010]}$ dependence of (c) the lattice constants and (d) the nesting vectors $q_{x}$ and $q_{y}$, as defined in panel (b).