Berry curvature origin of the thickness-dependent anomalous Hall effect in a ferromagnetic Weyl semimetal

Abstract

Magnetic Weyl semimetals with spontaneously broken time-reversal symmetry exhibit a large intrinsic anomalous Hall effect originating from the Berry curvature. To employ this large Hall current for room temperature topo-spintronics applications, it is necessary to fabricate these materials as thin or ultrathin films. Here, we experimentally demonstrate that Weyl semimetal Co2MnGa thin films (20–50 nm) show a large anomalous Hall angle ~11.4% at low temperature and ~9.7% at room temperature, which can be ascribed to the non-trivial topology of the band structure with large intrinsic Berry curvature. However, the anomalous Hall angle decreases significantly with thicknesses below 20 nm, which band structure calculations confirm is due to the reduction of the majority spin contribution to the Berry curvature. Our results suggest that Co2MnGa is an excellent material to realize room temperature topo-spintronics applications; however, the significant thickness dependence of the Berry curvature has important implications for thin-film device design.

Efficient room-temperature magnetization direction detection by means of the enhanced anomalous Nernst effect in a Weyl ferromagnet

“…In particular, ferromagnetic full Heusler compound Co 2 MnGa has shown the largest room-temperature value for S xy known to date, which is around 6.0 μV/K [9,10] in bulk single crystals and between 2.0 and 6.0 μV/K in thin films [11][12][13]. This joins a variety of interesting properties of Co 2 MnGa, such as a large anomalous Hall angle [14], large spin Hall angle [15], and a high resistance to oxidation [16], which pose it as a very promising material in the field of spintronics and spin caloritronics. In addition, it is also known that the transverse thermopower can be significantly enhanced by combining a Seebeck effect current and the anomalous Hall effect (AHE) in hybrid structures [17].…”

Unveiling transport properties of Co2MnSi Heusler epitaxial thin films with ultra-low magnetic damping

“…Small anomalous Hall angles were obtained compared with the Co2MnGa Heusler compound, which has been widely studied in the literature and for which a large 𝜃 𝐴𝐻𝐸 of ~10 % have been reported [50][51][52]. This can be explained by the weaker spin-orbit coupling in the Co2MnSi compound linked to its lower magnetocrystalline anisotropy compared to Co2MnGa.…”

Skyrmion generation and perpendicular magnetic anisotropy modification in Heusler alloy ultrathin films

“…Heusler alloys have low damping constant, high spin polarization and tunable properties which make them ideal for spintronics applications [10]. Very recently magnetic Weyl semimetals with emerging phenomena have been found in Heusler alloys [11,12]. This material shows a very large anomalous Hall angle which can be used a spin torque generator to drive skyrmion motion.…”

“…A chiral object cannot be superimposed onto its mirror image. The DMI energy can be written as follows 12) where D is the DMI coefficient.…”

“…In this thesis, the resistivity option of PPMS is employed to measure the longitudinal (R xx ) and Hall (R xy ) resistance with the standard four-wire or Van der Pauw geometry, as shown in Figure 2. 12. Thin films are mounted on resistivity pucks and placed on the horizontal rotator which enables a sample to be rotated over a full 360°in the presence of an applied magnetic field (up to ±9 T) and a controlled temperature (1.8 -400 K) (see Figure 2.13).…”