We present extensive first-principles calculations on the inverse full-Heusler compounds having the chemical formula X2YZ where (X = Sc, Ti, V, Cr or Mn), (Z = Al, Si or As) and the Y ranges from Ti to Zn. Several of these alloys are identified to be half-metallic magnets. We show that the appearance of half-metallicity is associated in all cases to a Slater-Pauling behavior of the total spin-magnetic moment. There are three different variants of this rule for the inverse Heusler alloys depending on the chemical type of the constituent transition-metal atoms. Simple arguments regarding the hybridization of the d -orbitals of neighboring atoms can explain these rules. We expect our results to trigger further experimental interest on this type of half-metallic Heusler compounds. PACS numbers: 75.50.Cc, 75.30.Et, 71.15.Mb The rise of nanotechnology and nanoscience during the last decade brought to the center of scientific research new phenomena and materials. Spintronics and magnetoelectronics compose one of the most rapidly expanding field in nanoscience. 1 Half-metallic magnetic compounds play a crucial role in this development. 2 These materials present usual metallic behavior for the one spin direction while an energy gap in the band structure is present in the other spin direction similarly to semiconductors. 3,4 The possibility of creating 100% spin-polarized current has triggered the interest on such compounds. 5 De Groot and collaborators in 1983 have initially suggested based on electronic structure calculations that NiMnSb, a semi-Heusler alloy, is a halfmetal 6 and since then several half-metallic compounds have been discovered. 7 Several aspects concerning the implementation of half-metallic alloys in realistic devices, like tunnelling magnetic junctions or giant magnetoresistive junctions and spin-injectors, have been discussed in literature. [8][9][10] The family of Heusler alloys incorporates more than 1000 members almost all crystalizing in a close-packed cubic structure similar to the binary semiconductors. 11 Most of them are metals exhibiting diverse magnetic phenomena. The lattice is a f.c.c. with four equidistant sites as basis along the diagonal of the unit cell. 3 There are two families of Heusler alloys. The semi-(or half-)Heuslers have the chemical formula XYZ where the sequence of the sites is X-Y-void-Z. The X and Y are transitionmetal elements and Z is a sp-element and the structure is known as the C1 b lattice. The second subfamily consists the full-Heusler compounds with the chemical formula X 2 YZ. When the valence of the X is larger than Y, the atomic sequence is X-Y-X-Z and the structure is the well known L2 1 one with prototype Cu 2 MnAl. 12 When the valence of the Y elements is the largest, the compounds crystallize in the so-called XA structure, where the sequence of the atoms is X-X-Y-Z and the prototype is Hg 2 TiCu. 12 The latter alloys are also known as inverse Heusler compounds. Several inverse Heuslers have been studied using first-principles electronic structure calculat...

We employ ab-initio electronic structure calculations to search for spin gapless semiconductors, a recently identified new class of materials, among the inverse Heusler compounds. The occurrence of this property is not accompanied by a general rule and results are materials specific. The six compounds identified show semiconducting behavior concerning the spin-down band structure and in the spin-up band structure the valence and conduction bands touch each other leading to 100% spin-polarized carriers. Moreover these six compounds should exhibit also high Curie temperatures and thus are suitable for spintronics applications.