Coexistence of spin semimetal and Weyl semimetal behavior in FeRhCrGe

Abstract

In this letter, we report the discovery of a new class of spintronic materials, namely spin semimetals (SSM), employing both theoretical and experimental tools. The band structure of this class of materials is such that one of the spin bands resembles that of a semi-metal, while the other is similar to that of an insulator/semiconductor. This report is the experimental verification of the first SSM, FeRhCrGe, a quaternary Heusler alloy with a magnetic moment 3 µB and a Curie temperature of 550 K. The measurement below 300 K shows nearly temperature independent conductivity and a relatively moderate Hall effect. SSM behavior for FeRhCrGe is also confirmed by rigorous first principles calculations. Band structure calculations also reveal that the spin up (semi metallic) band has combined features of type II Weyl and nodal line semimetal. As such, this study opens up the possibility of a new class of material with combined spintronic and topological properties, which is important both from fundamental and applied point of view.PACS numbers: 75.47.Np, 75.76.+j, 76.80.+y Introduction: Recent developments in magnetic Heusler alloys, such as the discovery of half metallic ferromagnets (HMF) have fuelled the area of spintronics research considerably. 1-5 One of the spin bands is metallic while the other is either semiconducting or insulating in this class of materials. Later, spin gapless semiconductors (SGS) 6 were discovered which gained prominence over the half metals due to their unique properties. Magnetic semiconductors 7 with unequal band gaps constitute another class of spintronic materials that produce high spin polarized charge carriers at elevated temperatures. Fully compensated ferrimagnet 8 is another unique class. In this letter, we discovered a new interesting class of materials, which we term as spin semi-metals (SSM). One of the main motives of this paper is to highlight the discovery of SSM and its importance and applications in the field of spintronics. We demonstrate the existence of necessary features of SSM in a realistic material, FeR-hCrGe. Furthermore, the spin up band of this material is also found to acquire a combined feature of type II Weyl 9,10 and nodal line 11,12 semi-metal.

Coexisting structural disorder and robust spin-polarization in half-metallic FeMnVAl

“…Among the experimentally reported members, only a few Co-based and Ni-based quaternary Heusler alloys are explored so far [9,10,15,16]. Research on Fe-based quaternary Heusler alloys is in its infancy [17], although some theoretical predictions exist [18][19][20]. Furthermore, the presence of structural disorder in various Heusler-based HMFs is quite inherent and it is almost impossible to obtain a disorder-free crystal structure.…”

Half-metallic ferromagnetism and Ru-induced localization in quaternary Heusler alloy CoRuMnSi

“…The ground state configuration I can be understood on the basis of empirical relation involving electronegativity, which suggests that the least electronegative ion occupies the octahedral site. 16,44 In Co-RuMnSi, Mn has the least electronegativity and hence favors the octahedral site while the intermediate elec- Figure 5 shows the spin-resolved density of states, band structures, band widths for the spin up band, and 3D band dispersion for configuration I of CoRuMnSi at its relaxed lattice parameter a 0 . The alloy manifests electronic structure of a fully spin-polarized half-metal.…”

“…Similar schematics of molecular interaction picture can also be noticed in FeRhCrGe alloys. 44 However, in CoRuMnSi alloy, we can notice the anomalies in the interaction/hybridization of atomic orbitals by carefully analyzing the projected atomic d orbital character at Γ point (see Fig. 6).…”

Bipolar magnetic semiconducting behavior in VNbRuAl

“…Later, spin gapless semiconductors (SGSs) [8,9] were discovered. Magnetic semiconductors (MSs) [10] and spin semimetals [11] constitute other unique classes. A number of these classes of materials have been reported by our group in the past [6][7][8][9]11].…”

“…Magnetic semiconductors (MSs) [10] and spin semimetals [11] constitute other unique classes. A number of these classes of materials have been reported by our group in the past [6][7][8][9]11]. In this paper, we report yet another interesting class, namely, bipolar magnetic semiconductors (BMSs).…”