Half Metals

Abstract

The classification of half‐metals is discussed taking account of both itinerant and localized electrons. The recent developments in the search for new half‐metals in oxides, nitrides, sulfides, and Heusler alloys are presented. The different experimental techniques for measuring spin polarization are summarized. The difficulties in measuring the spin polarization directly forced the exploration of other experimental techniques to identify a half‐metal, apart from an integral spin moment, metallic conduction criteria, and band‐structure calculations. The effect of surface/interface states on half‐metallicity is reviewed as the challenges remain in controlling the composition, defects, atomic ordering both in the bulk and at the interface. The possible applications of half‐metals, ideal sources of spin‐polarized electrons, in spin electronics are outlined.

Cubic MnSb: Epitaxial growth of a predicted room temperature half-metal

“…An ideal FM material would provide a fully spin polarized current [1] and should possess "engineering compatibility" with its SC host, which includes controllable epitaxy and interfaces, and suitability for device processing. Certain half-metallic ferromagnetic (HMF) materials have a density-of-states (DOS) spin polarisation at the Fermi level of P DOS = 100% due to the presence of a band gap straddling the Fermi energy E F for one spin channel only [2].…”

“…Certain half-metallic ferromagnetic (HMF) materials have a density-of-states (DOS) spin polarisation at the Fermi level of P DOS = 100% due to the presence of a band gap straddling the Fermi energy E F for one spin channel only [2]. Density functional theory (DFT) has predicted this property in several classes of materials [1], including Heusler alloys and transition metal pnictides (TMPs), at temperature T = 0K. On this basis, half-metallicity was first envisaged in NiMnSb, which has a minority spin gap E g ≈ 0.5 eV [3].…”

Distinctive Picosecond Spin Polarization Dynamics in Bulk Half Metals

“…This scenario has fostered a significant effort for studying the magnetization dynamics and the distinctive interplay between the metallic and the insulating spin channels in half-metals (HMs), such as Heusler compounds (e.g., Co 2 MnSi and Co 2 FeSi) and oxides [e.g., CrO 2 , La 2/3 Sr 1/3 MnO 3 , and Fe 3 O 4 (magnetite)] (see, e.g., Refs. [10][11][12] for reviews). This exotic dependence of the transport properties on the spin channels makes the physics of the HMs puzzling and striking [13,14].…”

Formation of MFe2O4 (M = Co, Ni and Mn) Films from MO / Fe2O3 Multilayers

“…In contrast to the spin polarization, optical pump-probe experiments can determine the demagnetization time τ m , which is related to the half-metallicity of the material [10]. The classification of different half-metals due to their transport characteristics was given by Coey et al [11]. The half-Heusler alloys, full-Heusler alloys and oxides are well known as highly (100%) spin-polarized materials [12][13][14][15].…”