Preprint

Formation of mid-gap states and ferromagnetism in semiconducting CaB$_6$

Jong‐Soo RhyeeCenter for Frontier Materials , Department of Materials Science and Engineering , Kwangju Institute of Science and Technology , Gwangju 500-712 KoreaB. H. OhCenter for Frontier Materials , Department of Materials Science and Engineering , Kwangju Institute of Science and Technology , Gwangju 500-712 KoreaB. K. ChoCenter for Frontier Materials , Department of Materials Science and Engineering , Kwangju Institute of Science and Technology , Gwangju 500-712 KoreaMyung‐Hwa JungMaterials Science Lab. Korea Basic Science Institute , Taedok Science Town , Taejon 305-333 KoreaH. C. KimMaterials Science Lab. Korea Basic Science Institute , Taedok Science Town , Taejon 305-333 KoreaYoon, Y. K.Institute of Physics of the Slovak Academy of SciencesJae Hoon KimDepartment of Physics , Yonsei University , Seoul 120-749 KoreaToshikazu EkinoFaculty of Integrated Arts and Sciences , Hiroshima University , Higashi-Hiroshima 739-8521 , Japan

2003en

Ochiq kirishYashil

ABI

Annotatsiya

We present a consistent overall picture of the electronic structure and ferromagnetic interaction in CaB$_6$, based on our joint transport, optical, and tunneling measurements on high-quality {\em defect-controlled} single crystals. Pure CaB$_6$ single crystals, synthesized with 99.9999 %-pure boron, exhibited fully {\em semiconducting} characteristics, such as monotonic resistance for 2--300 K, a tunneling conductance gap, and an optical absorption threshold at 1.0 eV. {\em Boron-related defects} formed in CaB$_6$ single crystals synthesized with 99.9 %-pure boron induced {\em mid-gap states} 0.18 eV below the conduction band and extra free charge carriers, with the transport, optical, and tunneling properties substantially modified. Remarkably, no ferromagnetic signals were detected from single crystals made with 99.9999 %-pure boron, regardless of stoichiometry, whereas those made with 99.9 %-boron exhibited ferromagnetism within a finite range of carrier density. The possible surmise between the electronic state and magnetization will be discussed.

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DOI: 10.48550/arxiv.cond-mat/0310068

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