Manipulating magnetism in the topological semimetal ${\mathrm{EuCd}}_2{\mathrm{As}}_2$

${\mathrm{EuCd}}_2{\mathrm{As}}_2$ is a magnetic semimetal that has the potential of manifesting nontrivial electronic states, depending on its low temperature magnetic ordering. Here, we report the successful synthesis of single crystals of ${\mathrm{EuCd}}_2{\mathrm{As}}_2$ that order ferromagnetically or antiferromagnetically depending on the level of band filling, thus allowing for the use of magnetism to tune the topological properties within the same host. We explored their physical properties via magnetization, electrical transport, heat capacity, and angle-resolved photoemission spectroscopy measurements and conclude that ${\mathrm{EuCd}}_2{\mathrm{As}}_2$ is an excellent, tunable system for exploring the interplay of magnetic ordering and topology.

Figure 1

Specific heat, resistivity, and magnetization data for FM-${\mathrm{EuCd}}_2{\mathrm{As}}_2$ and AFM-${\mathrm{EuCd}}_2{\mathrm{As}}_2$. (a)–(c) Magnetic field dependent magnetization with the field parallel to the $c$ axis (black filled circle) and perpendicular to the $c$ axis (red open circle) at 2 K for FM-${\mathrm{EuCd}}_2{\mathrm{As}}_2$, AFM-${\mathrm{EuCd}}_2{\mathrm{As}}_2$, and Sn flux grown AFM-${\mathrm{EuCd}}_2{\mathrm{As}}_2$, respectively. Inset shows the inverse susceptibility with Curie-Weiss fitting. (d) A comparison between the magnetic field dependent magnetization for the three samples, FM-${\mathrm{EuCd}}_2{\mathrm{As}}_2$, AFM-${\mathrm{EuCd}}_2{\mathrm{As}}_2$, and Sn flux grown AFM-${\mathrm{EuCd}}_2{\mathrm{As}}_2$, in the low-field regime between $-1000$ Oe and 1000 Oe. All the measurements shown were done with the field perpendicular to the $c$ axis. (e) Temperature dependent specific heat $C_P$ (black line, left axis) and resistivity derivatives (red line, right axis) for FM-${\mathrm{EuCd}}_2{\mathrm{As}}_2$. (f) Temperature dependent specific heat $C_P$ (black line, left axis), resistivity derivatives (red line, right axis), and $d(MT/H)/dT$ at $H_{\parallel c}=50$ Oe (blue line, the second right axis) for AFM-${\mathrm{EuCd}}_2{\mathrm{As}}_2$.

Figure 2

Magneto-optical image of FM(salt)-${\mathrm{EuCd}}_2{\mathrm{As}}_2$. (a) Imaged at $T=8$ K, ferromagnetic domains (brown and green colors) appear below $T_C$. (b) Absence of domains above the magnetic transition, here imaged at $T=70$ K. Copper-color area on the left in each image is the copper sample holder.

Figure 3

ARPES measurement of the band structure of FM(salt)-${\mathrm{EuCd}}_2{\mathrm{As}}_2$, AFM(salt)-${\mathrm{EuCd}}_2{\mathrm{As}}_2$, and AFM(Sn)-${\mathrm{EuCd}}_2{\mathrm{As}}_2$. ARPES intensity plot along a cut through the gamma point for (a) FM(salt) at $T=40$ K. (b) AFM(salt) at $T=40$ K. (c) Electronic structure of AFM(Sn) at $T\sim 11$ K. (d) Energy distribution curve at the zero momentum of FM(salt), AFM(salt), and AFM(Sn) with black, red, and blue lines, respectively. Dashed lines indicate the energy of the top of the inner hole band for FM(salt) and AFM(salt). (e) Momentum distribution curves (MDCs) at $E_F$ of FM(salt), AFM(salt), and AFM(Sn) with black, red, and blue lines, respectively. Dashed lines [black for FM(salt), red for AFM(salt), and blue for AFM(Sn)] are indicating the peak positions of MDCs that mark the value of the Fermi momentum.

Figure 4

HAADF-STEM and EDS analysis of FM(salt)-${\mathrm{EuCd}}_2{\mathrm{As}}_2$ and AFM(salt)-${\mathrm{EuCd}}_2{\mathrm{As}}_2$ along [21 $\overline{1}\overline{0}$] zone axis. (a) High-resolution HAADF-STEM image of FM(salt) superimposed with color composite EDS elemental maps, and overlaid atomic model. (b)–(d) Atomically resolved EDS map of Eu, Cd, and As taken from the same area of (a). (e),(f) High-resolution HAADF image of FM(salt) and AFM(salt), respectively. (g),(h) Line profiles showing the image intensity (normalized to equal one for the As column) as a function of position in image (e) along ${\text{A-A}}^{\prime }$ and ${\text{B-B}}^{\prime }$, and positions in image (f) along ${\text{C-C}}^{\prime }$ and ${\text{D-D}}^{\prime }$, respectively. (i),(j) Histogram of the intensities of atomic image maxima in the area of (e) and (f), respectively.