Browsing by Author "Markou, Anastasios"

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Heteroepitaxy of Co-Based Heusler Compound/Muscovite for Flexible Spintronics
(2019-09-25)
Chen, Yi-Cheng
;
Yen, Min
;
Lai, Yu-Hong
;
Markou, Anastasios
;
Zhang, Liguo
Materials with high spin-polarization play an important role in the development of spintronics. Co-based Heusler compounds are a promising candidate for practical applications because of their high Curie temperature and tunable half-metallicity. However, it is a challenge to integrate Heusler compounds into thin film heterostructures because of the lack of control on crystallinity and chemical disorder, critical factors of novel behaviors. Here, muscovite is introduced as a growth substrate to fabricate epitaxial Co2MnGa films with mechanical flexibility. The feature of heteroepitaxy is evidenced by the results of X-ray diffraction and transmission electron microscopy. Moreover, high chemical ordering with superior properties is delivered according to the observation of large Hall conductivity (680 Omega(-1) cm(-1)) and highly saturated magnetic moment (similar to 3.93 mu(B)/f.u.), matching well with bulk crystals. Furthermore, the excellence of magnetic and electrical properties is retained under the various mechanical bending conditions. Such a result suggests that the development of Co2MnGa/muscovite heteroepitaxy provides not only a pathway to the thin film heterostructure based on high-quality Heusler compounds but also a new aspect of spintronic applications on flexible substrates.
Large anomalous Nernst effect in thin films of the Weyl semimetal Co2MnGa
(2018-11-19)
Reichlova, Helena
;
Schlitz, Richard
;
Beckert, Sebastian
;
Swekis, Peter
;
Markou, Anastasios
The magneto-thermoelectric properties of Heusler compound thin films are very diverse. Here, we discuss the anomalous Nernst response of Co2MnGa thin films. We systematically study the anomalous Nernst coefficient as a function of temperature, and we show that unlike the anomalous Hall effect, the anomalous Nernst effect in Co2MnGa strongly varies with temperature. We exploit the on-chip thermometry technique to quantify the thermal gradient, which enables us to directly evaluate the anomalous Nernst coefficient. We compare these results to a reference CoFeB thin film. We show that the 50-nm-thick Co2MnGa films exhibit a large anomalous Nernst effect of -2 mu V/K at 300 K, whereas the 10-nm-thick Co2MnGa film exhibits a significantly smaller anomalous Nernst coefficient despite having similar volume magnetizations. These findings suggest that the microscopic origin of the anomalous Nernst effect in Co2MnGa is complex and may contain contributions from skew-scattering, side-jump, or intrinsic Berry phase. In any case, the observed anomalous Nernst coefficient of -2 mu V/K at 300 K is large compared to the values measured in other thin films and makes this material system a very promising candidate for efficient spin-caloritronic devices. Published by AIP Publishing.
Thickness dependence of the anomalous Hall effect in thin films of the topological semimetal Co2MnGa
(2019-08-19)
Markou, Anastasios
;
Kriegner, Dominik
;
Gayles, Jacob
;
Zhang, Liguo
;
Chen, Yi-Cheng
Topological magnetic semimetals promise large Berry curvature through the distribution of the topological Weyl nodes or nodal lines and further novel physics with exotic transport phenomena. We present a systematic study of the structural and magnetotransport properties of Co2MnGa films from thin (20 nm) to bulklike behavior (80 nm) in order to understand the underlying mechanisms and the role of topology. The magnetron sputtered Co2MnGa films are L2(1)-ordered showing very good heteroepitaxy and a strain-induced tetragonal distortion. The anomalous Hall conductivity was found to be maximum at a value of 1138 S/cm, with a corresponding anomalous Hall angle of 13%, which is comparatively larger than topologically trivial metals. There is good agreement between the theoretical calculations and the Hall conductivity observed for the 80 nm film, which suggests that the effect is intrinsic. Thus, the Co2MnGa compound manifests as a promising material for topologically driven spintronic applications.