New half-metallic materials with an alkaline earth element

Abstract

New candidates for half-metallic materials were theoretically designed recently by Geshi et al. The materials are calcium pnictides, i.e. CaP, CaAs and CaSb. When the zinc-blende structure was assumed, these compounds showed half-metallic electronic band-structure, in which a curious flat band was found. To explain this magnetism, we investigated characters of orbitals on this flat band of CaAs. The hybridization of p states of As with d states of Ca is shown to be essential for formation of a flat band made of localized orbitals. The appearance of complete spin polarization in the flat band suggests that the flat-band mechanism is relevant for the ferromagnetism. A connection from the first-principles result to a solvable Hubbard model with a flat band is discussed.

Symmetry Induced Half-Metallic Alkaline Earth Ferromagnets

“…4, the half-metallicity is maintained by the majority spin channel accompanied by the empty minority spin bands. In conclusion, replacement of carbon by boron produced the decrease in the number of valence electrons (per formula unit) by one and subsequent creation of local magnetic moment of 3 µ B on B, conserving the general mechanism of half-metallicity described in earlier publications [1][2][3][4]6].…”

“…Recently, an unusual class of ferromagnetic materials [1][2][3] which do not contain transition-metal or rare-earth atoms was proposed and analysed theoretically by ab initio calculations. The predictive power of these calculations has been successfully used to investigate the properties of binary compounds like MgC, CaC, SrC and BaC [4].…”

Breakdown of half-metallic ferromagnetism in zinc-blende II-V compounds: First-principles calculations

“…So far there have been a few reports on the fabrication of nano-scale MnAs dots on GaAs, CrSb ultra-thin films on the GaSb substrate, and ultra-thin CrAs layers in the CrAs/GaAs multilayers 2,3,4,5 . In addition, the half-metallic ZB compounds with transition-metal elements were also reported by first-principles density-functional-theory (DFT) calculations, 8 whereas a high Curie temperature above 400 K has been observed in experiments for CrAs and CrSb systems 2,3 .Contrary to the ZB compounds containing transition-metal elements, where the localized d electrons are responsible for the ferromagnetic component in HMF, several DFT calculations have predicted another kind of ZB II-V compounds as a candidate for the HMFs without containing any transitionmetal element 10,12,13 . The ZB compounds of alkaline earth elements Ca, Sr, and Ba combined with all the elements of the group V were shown to be HMFs with a magnetic moment of one Bohr magneton (µ B ) per formula unit-cell (f.u.).…”

“…Contrary to the ZB compounds containing transition-metal elements, where the localized d electrons are responsible for the ferromagnetic component in HMF, several DFT calculations have predicted another kind of ZB II-V compounds as a candidate for the HMFs without containing any transitionmetal element 10,12,13 . The ZB compounds of alkaline earth elements Ca, Sr, and Ba combined with all the elements of the group V were shown to be HMFs with a magnetic moment of one Bohr magneton (µ B ) per formula unit-cell (f.u.).…”

“…To explore possible spintronics applications of HMFs to semiconductor devices, there have been a great deal of studies exploiting the half metallicity in the binary compounds of zinc-blende (ZB) structure 2,3,4,5,6,7,8,9,10,11,12,13 , which is simple and compatible with existing III-V and II-VI semiconductors. So far there have been a few reports on the fabrication of nano-scale MnAs dots on GaAs, CrSb ultra-thin films on the GaSb substrate, and ultra-thin CrAs layers in the CrAs/GaAs multilayers 2,3,4,5 .…”