Perovskites half-metallicity

Magnetic B-site ordered perovskites are of interest in at least two contexts, half-metallic ferromagnets , which show a large MR due to intergrain effects, and geometric magnetic... 

In the last decade, study of double perovskites has accelerated with the discovery of tunneling magnetoresistive (TMR) effects in Sr2FeMo06.i56N. Both the magnetism and transport in these oxides is strongly influenced by the cationic nature and the order/disorder of the ions at the B-site. Ferromagnetism and half-metallic properties are often... 

In this chapter the focus is upon electronic conductivity in perovskites. The electrons in perovskites are believed to be strongly correlated that is, they do not behave as a classical electron gas, but are the subject to electron-electron interactions. This leads to considerable modification of the collective electron behaviour of the conduction electrons, resulting in metal-insulator transitions, high-temperature superconductivity, half-metals and colossal magnetoresistance (CMR). The effects of strong correlation are important for the 3d, 4d and4f elements. In many ways the topics described here are thus a continuation of the previous chapter on magnetic perovskites, and in truth the two subject areas cannot be separated in a hard and fast maimer. 

Half-metallic materials, including perovskites, are discussed in ... 

Tlie plienomenon of half-metallicity has gained much interest in order to understand the unusual band structures in various classes of materials and their potential applications in future electronic devices. For example, zinc blend pnictides and chalcogenides e.g. CrAs) are another class of non-oxide materials (apart from Heuslers) in addition to the many oxide classes that are potentially half-metallic materials. Alkali metal doped rare earth oxomanganates, (REi- A MnOs), rutile-Cr02, spinel-Fe304 and Sr2peMo06 double perovskite oxide are examples of important half-metallic oxides. 

Due to its metallic and FM property, similar to double perovskites (see later), Cr02 is of great interest to material scientists and physicists. A computed band structure of Cr02 is shown in Figure 5.6. The Fermi level crosses the majority-spin band while it lies in a gap of the minority-spin density of states (DOS). Therefore, Cr02 is half-metallic on the basis of electronic structure calculations. The same band structure has been reproduced by several groups since it was first demonstrated by... 

Half-Metallic Antiferromagnetic (HMAFM) Double Perovskites... 

As it was already mentioned, the ordered double perovskite St2FeRe06 is also predicted to have a half-metallic ground state. The observed Ms of 2.7 pB/f-u. at 4.2 K is smaller than expected (3 pB/f-u.) for an antiferromagnetic coupling between Fe (d ) and Subsequent to the... 

The magnetic properties of half-metallic Sr2FeMo06 and related double perovskites cannot be explained on the basis of conventional and... 

While an ordered sample ( 91%) of Sr2FeMo06 showed a sharp low-field MR response, it was much lower in a partially disordered ( 31%) sampleJ Therefore, its absence in the disordered phase indicates the obliteration of HMF property due to large AS disor-der. Thus, ordering in double perovskite is crucial for the true nature of the half-metallic ground state and the intrinsic properties of the material. 

Chemical stability indicates that in the cubic, metallic perovskites the interstitial C and N are probably neutral. They represent, therefore, an M atom with half filled p or s-p orbitals, and in the cubic structure the metal-M-metal interaction is defined by Figure 86. [This is to be contrasted with low-temperature CrN, which has considerable ionic character and an ordering of its covalent character along a given axis.] In contrast to the M atoms of the Heusler alloys, the p electrons of C and N correlate with, and therefore spin pair, the near-neighbor eg electrons. The metal- -metal interactions are determined by the Ug electron-spin correlations since Hu 2.76 A < Rc. 

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