Thermodynamic and transport properties of high-quality single crystals of the altermagnet CrSb

Abstract

Altermagnetism (AM) is an emerging magnetic order unifying essential characteristics of ferromagnetic and antiferromagnetic states. Despite zero net magnetization, altermagnets (AMs) exhibit spin-split electronic bands and lifted altermagnon spin degeneracy. The altermagnet CrSb has attracted significant interest owing to its large spin-splitting energy. In this paper, we present the growth details of high-quality single crystals of CrSb using the self-flux method. We obtained large (001) oriented hexagonal crystals, up to 2 $\times$ 2.5 $\times$ 1 mm$^3$ in size. We investigated physical properties of the CrSb single crystals through measurements of electrical resistivity, magnetic susceptibility, and specific heat. The residual resistivity ratio (RRR) around 11 indicating the higher crystal quality than previous reports. A pronounced positive magnetoresistance of up to 80\% is observed at 3.5 K. The specific heat was measured down to 0.45 K, revealing the Sommerfield coefficient $γ$ = 4.0 $\pm$ 0.08 mJ mol$^{-1}$ K$^{-2}$, indicating weak electronic correlation among the conduction electrons. The room temperature specific heat exceeds the Dulong-Petit limit due to a broad magnon contribution from the altermagnetic order. The data yield the Debye temperature of 321 $\pm$ 5 K and magnon energy gap $\sim$ 16 $\pm$ 1 meV. We also reveal that stoichiometric CrSb does not exhibit superconductivity down to 0.1 K. These findings underscore CrSb as a viable altermagnet for room temperature magnonic and spintronic applications.

Figures (5)

• Figure 1: (a) Schamatic diagram of crystal and magnetic structures drawn by VESTA rodriguez1993recent. Opposite-spin sublattices are denoted as Cr$_1$ (blue: spin-up) and Cr$_2$ (red: spin-down), with Sb atoms shown as grey spheres. (b) Schematic view of symmetry-driven sublattice interchange in CrSb. The two magnetic sublattices are related through either a screw operation accompanied by a half unit cell translation along the $c$ direction or a mirror operation with respect to a plane perpendicular to the $c$ axis.
• Figure 2: Schematic description of the CrSb single crystal growth process based on the self-flux method. (a) Raw materials (Cr and Sb) are placed in a crucible inside a quartz ampoule for thermal treatment. (b) Upon heating, the flux melts, and CrSb crystals form. (c) The quartz ampoule is inverted by 180$^{\circ}$ and centrifuged to separate the residual flux from the CrSb crystals.
• Figure 3: (a) Laue diffraction pattern of a CrSb crystal, showing a diffraction pattern characteristic of the (001) plane. Inset: optical image of the CrSb single crystal. (b) Result of energy dispersive spectroscopy (EDS) of the same crystal indicating a stoichiometric CrSb composition. (c) Powder XRD pattern of crushed CrSb single crystals (black points), shown together with the simulated profile (red curve). The difference between the experimental and simulated intensities is also shown with the blue curve. The green vertical lines represent the calculated Bragg reflection positions. The near coincidence of the two green bars arises from the $K_{\alpha_1}$ and $K_{\alpha_2}$ characteristic X-ray emission lines.
• Figure 4: (a) Temperature dependence of the zero-field longitudinal resistivity. (b) MR at various temperatures ranging in 3.5$-$300 K for $H \parallel c$ and $I\parallel x$. (c) Kohler’s plots of the MR at different temperatures. (d) Temperature dependence of the DC magnetic susceptibility (1.8$-$300 K) for $H\perp$$c$. (d) Field-dependent magnetization measured at various temperatures for $H \parallel$$c$ and $H\perp$$c$. (e) Susceptometer signal, which is proportional to the AC susceptibility, for a single crystal of CrSb. This measurement was performed using an AC excitation current of 0.50 mA rms ($\sim$ 17 $\mu$T rms) at a frequency of 3.011 kHz.
• Figure 5: (a) $C$/T plotted against $T^2$ from 0.45 to 20 K. Data is fitted with \ref{['eq2']}. We also show the result of fitting with $C=\gamma T +\beta T^3$ below 8 K (blue broken curve). (b) Temperature-dependent specific heat of a CrSb crystal measured between 1.8 K and 300 K under zero magnetic field. The black dashed line corresponds to the Dulong Petit limit. The red solid line represents the fit obtained over the temperature range 25$–$300 K using \ref{['eq7a']}. The black and blue solid curves indicate the individually extracted lattice and magnon contributions, respectively. (c) Specific heat results from several samples. The solid curves are the result of fitting with \ref{['eq7a']}. The specific heat of RuO$_2$, expressed as ($C/T$), is plotted as a function of $T^{2}$ for temperatures between 0.5 and 10 K under a 5 T magnetic field applied along the [001] and [100] crystallographic directions. The data for the different orientations overlap within experimental accuracy, indicating isotropic behavior.