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3 Acta Physica Polonica A

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Superconductivity Study of GaN Highly Doped by Transition Metals

100%

Gosk J. , Boćkowski M. , Tokarczyk M. , Kowalski G. , Twardowski A.

Acta Physica Polonica A

2013

tom 124

nr 5

877-880

GaN:Cr and GaN:Fe single crystals as well as GaN:Mn micropowders highly doped by transition metals were grown to investigate low temperature superconductivity. Magnetic measurements revealed type I superconductivity with T_{C} ≈ 6 K and H_{C} ≈ 600 Oe, identical for all compounds and also identical to that observed before in GaP:Cr and GaAs:Cr. The presence of amorphous inclusions of gallium may explain existing superconductivity as a result of a phase transition leading to β-Ga during cooling down of the sample. Since the observed parameters are close to those characteristic for superconducting Ga(II) this possibility could not be ruled out.

Observation of Superconductivity in Highly Cr-Doped GaP Single Crystals

86%

Gosk J. , Strzelecka G. , Kowalski G. , Hruban A. , Kamińska M. , Twardowski A. , Gronkowski J.

Acta Physica Polonica A

2006

tom 110

nr 2

189-193

Studying bulk GaP, highly doped with Cr, and searching for possible ferromagnetic semiconductor in view of spintronic applications, we found superconducting behavior of this material unexpectedly. Magnetization techniques and X-ray diffraction were applied to study these crystals. Magnetization revealed superconducting features up to about 6 K and X-ray studies showed that superconductivity might be related to small size Cr precipitates.

Observation of Magnetic Anisotropy in GaN:Cr Single Crystals

86%

Gosk J. , Boćkowski M. , Kowalski G. , Grzegory I. , Szczytko J. , Twardowski A.

nr 6

1007-1009

Magnetic properties of bulk wurtzite GaN:Cr single crystals were studied with the magnetic field applied parallel and perpendicular to the crystal wurtzite c-axis. Structure of the crystal was examined by the X-ray diffraction method. Strong anisotropy of magnetization at low temperatures (2-10 K) was observed. The experimental data suggest Cr to be in nonspherical d^4 configuration.

Magnetization of GaMnN Ceramics Prepared from Nanopowders by an Anaerobic Synthesis and High-Pressure High-Temperature Sintering

86%

Gosk J. , Drygaś M. , Janik J. , Gierlotka S. , Pałosz B. , Twardowski A.

Acta Physica Polonica A

2016

tom 129

nr 1a

A-103-A-106

Herein, we report a study on magnetic properties of GaMnN ceramics prepared by no additive high-pressure high-temperature sintering of a range of nanopowders, the latter made via an anaerobic synthesis method in the Ga/Mn bimetallic system at various nitridation temperatures and different levels of initial Mn concentration. Measurements of the magnetization as a function of temperature and magnetic field for the ceramics and parent nanopowders showed a typical paramagnetic behavior. Antiferromagnetic interactions between Mn-ions incorporated in the GaN lattice, GaMnN, were revealed and shown to be much stronger in the ceramics than in the respective nanopowders. In addition, in all of these materials an antiferromagnetic contribution originating from a residual Mn₂SiO₄ by-product was also observed. The highest calculated Mn concentration in the nanopowders reached 3.4 at.%. Complex mixtures of gallium nitride polytypes with multimodal particle size distributions in the nanosized range (small nano: 2-8 nm, large nano: 35-60 nm) were converted upon sintering to the single hexagonal GaN phase with average crystallite sizes of 40-80 nm and higher. For the optimal 700°C-treated materials, the Mn concentration in the parent GaMnN nanopowder was 3.2 at.% whereas in the derived ceramics it amounted to 5.5 at.%. At the same time, contributions of the adventitious Mn₂SiO₄ by-product significantly decreased upon sintering.