Observation of Superconductivity in Highly Cr-Doped GaP Single Crystals
| Autor: | G. Strzelecka, A. Hruban, Grzegorz Kowalski, Andrzej Twardowski, J. Gosk, J. Gronkowski, Maria Kaminska |
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| Rok vydání: | 2006 |
| Předmět: | |
| Zdroj: | Acta Physica Polonica A. 110:189-193 |
| ISSN: | 1898-794X 0587-4246 |
| DOI: | 10.12693/aphyspola.110.189 |
| Popis: | Studying bulk GaP, highly doped with Cr, and searching for possible ferromagnetic semiconductor in aim of spintronic applications, we found superconducting behavior of this material unexpectedly. GaP bulk crystals intentionally doped with Cr were grown by Liquid Encapsulated Czochralski (LEC) method. Metallic chromium was added to the melt with concentration in the range of 1 to 6x10 20 cm -3 . The resulting crystals were highly resistive at room temperature. X-ray diffraction (XRD) and magnetization techniques were applied to study these crystals. XRD measurements on (111) oriented samples employed high resolution multicrystal diffractometer and X-ray topography in classical transmission mode. Diffractometric results indicated good overall crystalline quality of the samples with some possible lattice parameter gradient. Transmission topography revealed network of "cellular structure", usually observed in LEC grown GaAs crystals. This type of structure is well known to contain intentional or nonintentional dopants and other defects, segregated within the cell walls. It is highly possible that excess Cr was grouped in these regions. Magnetization studies were performed as a function of magnetic field, up to 6 T, and in the temperature range of 2-100 K, using SQUID magnetometer. All samples showed paramagnetic behaviour described well by the Brillouin function and ascribed to Cr impurity in GaP. Maximal Cr concentration calculated from saturation of magnetization curve was about 0.01%. Small antiferromagnetic (AFM) contribution to the total observed magnetization signal were found for samples with high initial Cr contents. It resulted most probably from metallic Cr precipitates. Chromium is known to be AFM element with Neel temperature TN=312K. However, unexpectedly, the total magnetization signal measured at T=2K was dominated by a quite strong diamagnetic response at low magnetic field. Moreover, typical behavior of superconductive system, i.e., diminishing of diamagnetic response at some critical magnetic field Bc, as well as characteristic Bc dependence on temperature was observed. We relate the observed superconductivity features to Cr precipitates, of peculiar shape and size, embedded in GaP lattice. Up to now there have been only reports about chromium superconductors with transition temperatures up to 10K in metastable fcc phase, fabricated by epitaxially sandwiching Cr between gold layers or in ion beam deposited Cr thin films on soft glass. Bulk Cr metal is not a superconductor. In recent years several ways to cause non superconducting elements to superconducting state have been found, including application of pressure, irradiation, quenched growth on a cold substrate, epitaxial templating in the form of thin film or chemical doping. This is the first report of Cr superconductivity in semiconductor host. It seems worth further studies because of interesting physics as well as possible applications including superconducting interconnections, junctions, and switches in integrated semiconductor-based devices. |
| Databáze: | OpenAIRE |
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