Charge Density Wave Transition in EuAl₄

Spin order and fluctuations in the EuAl4 and EuGa4 topological antiferromagnets: A μSR study

“…Among these materials, the Eu-4 f electrons bring new intriguing aspects to the topology. Both EuAl 4 and EuGa 4 are antiferromagnets below their critical temperatures T N = 15.6, and 16.4 K, respectively, with the former also undergoing a CDW transition at T CDW ∼ 140 K [6][7][8][9][10][11][12]. Further, while EuGa 4 exhibits only one antiferromagnetic (AFM) transition, EuAl 4 undergoes four subsequent AFM transitions below T N .…”

Giant magnetoresistance and topological Hall effect in the EuGa4 antiferromagnet

“…The multiband nature of EuGa 4 is clearly evident from the nonlinear behavior of ρ x y (H) [see e.g., ρ x y (H) at 20 K in figure 5(f)], as confirmed also by de Haas-van Alphen (dHvA) studies and by electronic band-structure calculations [48,49,52]. Similar to BaAl 4 and EuAl 4 [44,46,47], at high temperatures, the ρ x y (H) of EuGa 4 is dominated by the holes while, at low temperatures, mostly the electrons account for the Hall signal. In the AFM state [see figures 5(a)-(d)], a hump-like anomaly in the ρ x y (H) gradually develops with decreasing temperature, reminiscent of the topological Hall resistivity arising from topological spin textures [3,17,19,21,23,24,25,26,27,28,29,31].…”

“…While in EuGa 4 , as shown in figure 6(b), the THE shows up between 4 and 7 T. Therefore, the critical field to induce the THE in EuAl 4 is about 3 times smaller than in EuGa 4 . On the other hand, a CDW order sets in at T CDW ∼ 140 K at ambient pressure in EuAl 4 [46,47,48,49,50,51], whereas physical-or chemical pressure is necessary to induce the CDW order in EuGa 4 [49,52,64]. The T CDW decreases with increasing pressure in EuAl 4 , while it does exactly the opposite in EuGa 4 [49,52].…”

“…Unlike these nonmagnetic materials, upon replacing Ba (or Sr) with Eu, the 4 f electrons bring new intriguing aspects to the topology, as clearly illustrated by our recent work on EuAl 4 [46]. EuAl 4 exhibits coexisting antiferromagnetic-(AFM) and CDW orders with onset temperatures of T N ∼ 15.6 K and T CDW ∼ 140 K [46,47,48,49,50,51] and undergoes a series of metamagnetic transitions in the AFM state [46,49]. Within the ∼1-2.5 T field range, a clear hump-like anomaly was observed in the Hall resistivity, most likely a manifestation of THE [46].…”

Charge-Density-Wave Order and Multiple Magnetic Transitions in Divalent Europium Compound EuAl$_4$

“…Indeed, a decrease in carrier density below this transition was revealed by both the magnetoresistance and Hall effect. 19) The second-order magnetic transition occurs at T N1 =15.4 K, which is followed by the remaining three successive magnetic transitions in a narrow temperature range, namely at T N2 =13.2 K, T N3 =12.2 K, and T N4 =10.0 K. The magnetic susceptibility shows several kinks at the corresponding transition temperatures along both the ab-plane and c-axis. The consecutive magnetic transitions in EuAl 4 are also confirmed in the magnetization curve, where four-step magnetic transitions were observed along the c-axis at 2 K. The specific heat exhibits a distinct λ-type anomaly at T N1 and an abrupt jump at T N3 , indicating the secondand first-order nature of the transition, respectively, whereas anomalies at T N2 and T N4 were small in magnitude.…”