Generalized Slater-Pauling rule for the inverse Heusler compounds

Abstract

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...

Slater-Pauling behavior in LiMgPdSn-type multifunctional quaternary Heusler materials: Half-metallicity, spin-gapless and magnetic semiconductors

“…13 In the case of inverse Heuslers, it is possible to get a M t ¼ Z t À 18 rule when X is Sc or Ti (and in some X ¼ V compounds also) since the t 1u states are high in energy and are unoccupied. 14 The same occurs for the LiMgPdSn-type compounds under study. When X 0 ¼ V, Y ¼ Ti, and Z ¼ Al or Si, the t 1u states are high in energy and are unoccupied leading to the M t ¼ Z t À 18 variant of the rule.…”

“…12 In the case of full-Heusler alloys with four atoms per unit cell, such relations have been derived both for the usual full Heusler compounds (chemical formula is X 2 YZ, where X and Y are transition-metal atoms and Z a sp-element) as well as the so-called inverse Heusler compounds (same chemical formula but the valence of X is lower than Y and the sequence of the atoms in the basis changes). 13,14 Slater-Pauling rules connect directly the electronic to the magnetic properties of half-metallic magnets and thus allows to determine the half-metallic character through magnetization measurements. Moreover, some of the inverse Heusler compounds have been identified to be also spin-gapless semiconductors (SGSs) where the spin-up band structure instead of being metallic presents a zero-gap semiconducting behavior; 15 Mn 2 CoAl a predicted SGS has been successfully synthesized.…”

Antiferromagnetic phase of the gapless semiconductorV3Al

“…[2,6,7] The D0 3 structure has the same space group as the L2 1 structure, but the binary D0 3 structure has a X 3 Z basis, while the ternary L2 1 structure has a X 2 YZ basis. Figure 1(c) illustrates the D0 3 structure of V 3 Al where the Al atom occupies the 4a Wyckoff position at (0,0,0), the V atom labeled V1 occupies the 4b position at (1/2, 1/2, 1/2), and the remaining two V atoms labeled V2 occupy the 8c position at (1/4, 1/4, 1/4).…”

“…Recent theoretical work on SGS Heusler compounds in the inverseHeusler structure has predicted that several of these materials can be antiferromagnetic (AF) gapless semiconductors and half-metallic antiferromagnets (HMAF; also known as fully-compensated half-metallic ferrimagnets). [6,7] Gapless semiconductors are a class of materials where the conduction and valence bands are separated by <0.1 eV band gap. Examples of gapless semiconductors include graphene, HgTe, α-Sn and some half-metallic Heusler compounds.…”

Magnetic properties of low-moment ferrimagnetic Heusler Cr2CoGa thin films grown by molecular beam epitaxy

“…3,4 There has been experimental and theoretical research on SGS materials that are either ferromagnetic or ferrimagnetic with a large overall magnetic moment. [5][6][7][8][9] However, for high density spintronic technologies, a low magnetic moment is preferable in order to minimize interactions while maintaining spin polarization as in the case of Mn 2 Ru x Ga.…”