Suppression of the gap energy in Zr-Ni-Sn and Ti-Ni-Sn by partial substitution of Zr and Ti by Ce

Abstract

We report on magnetic measurements and electronic structure investigations of the alloyed compounds Zr-Ni-Sn and Ti-Ni-Sn. Both belong to the group of semi-Heusler alloys, and are classified as narrow-gap semiconductors with indirect gaps near 500 meV. Tetravalent ions ͑Zr,Ti͒ are partly replaced by Ce, with a Ce concentration less than 20%. Susceptibility measurements indicate the magnetic ground state of Ce in both Zr-Ni-Sn and Ti-Ni-Sn, and the effective moment is near the trivalent value at Tϭ300 K. The Ce 4 f 1 configuration is well accepted by Ce 3d x-ray photoemission spectra. We compare the x-ray photoemission spectroscopy valence-band spectra for investigated Ce alloys. A very good agreement between the experiments and calculations is obtained. We classify Zr-Ni-Sn and Ti-Ni-Sn as alloys with a strong hybridization influence on the gap formation. The destructive alloying affecting the gap stability seems to have the same origin as in the case of Ce Kondo insulators. ͓S0163-1829͑98͒07115-X͔

Band Gap Stability in Kondo Insulators

“…In Ref. [12] we have argued that the lowering of the valence of Zr or Ti in the Ce-dopped samples closes the gap at CF. We believe that the reasons leading to the gap in the semi-Heusler alloys of the ZrNiSn-type and in the Ce-Kondo insulators seem to be similar.…”

“…We argued in Refs. [11,12] that the occupation number of . Ce f orbital, when it is smaller than 1, correlates with formation of the gap.…”

“…Recently, we have discussed the mixed valence of Ce in CeNiSn and CeRhSb [11][12][13], which seems to be very important for the formation of the gap. In this class of compounds in almost every case there is an isostructural semiconductor in which the 4f-element is replaced by a nοn-4 f tetravalent element.…”

The Electronic Structure and Magnetic Properties of Full- and Half-Heusler Alloys

“…The electronic structure of the half-metallic Heusler alloys was studied last decade by experimental and theoretical approaches [28][29][30][31][32][33] but basically the linearized muffin-tin orbital method was used with limitation for shape approximation for crystal potential excepting paper Ref. 30), where the fullpotential screened Korringa-Kohn-Rostoker method was applied.…”

“…[21][22][23][24][25][26][27] The similar tendency is observed for half-metallic Heusler alloys. [28][29][30][31][32][33] The calculations were mainly performed using the local spin density approximation (LSDA), which are known to be underestimated lattice constants and provide smaller magnetic moments. In present paper we report the results of ab-initio calculations of the electronic structure and structural and magnetic properties in different series of Heusler alloys based on Fe-, Co-and Mn, focusing on the effects of their composition and s-p Z atom and extend our study on the halfHeusler alloys also using the full-potential approach within the generalized gradient approximation (GGA) for exchange correlation potential.…”