K. Bouziane

Magnetic properties of Mn-implanted 6H-SiC single crystal

The electronic and magnetic structures of Mn-doped 6H-SiC have been investigated using ab initio calculations. Various configurations of Mn sites and vacancy types have been considered. The calculations showed that a substitutional Mn atom at either Si or C sites possesses a magnetic moment. The Mn atom at Si site possesses larger magnetic moment than Mn atom at C site. The magnetic properties of ferromagnetically and antiferromagnetically coupled pair of Mn atoms in the presence of vacancies have also been explored. Our calculations show that antiferromagnetically coupled pair of Mn atoms at Si sites with neighboring C vacancy is magnetically more stable. Relaxation effects were also studied. The results are correlated to the measured magnetic properties obtained for Mn-implanted 6H-SiC for various Mn concentrations.

Model for Mn in 6H-SiC from first-principle studies

The electronic and magnetic properties of 6H-SiC with Mn impurities have been calculated using generalized gradient approximation formalism. Various configurations of Mn sites and Si and C vacancies were considered. It was found that 6H-SiC doped with Mn atoms possess a moment for both types of substitution. The Mn atom at Si site possesses larger magnetic moment than Mn atom at C site. The energy levels appearing in the band gap due to vacancies and due to Mn impurities are determined and the calculated densities of states are used to analyze the different values of the magnetic moments for different types of substitution. A model that explains the magnetic moment at Mn site is proposed.

Magnetic properties of nanocrystalline FexCu1-x alloys prepared by ball milling

X-ray diffraction, Mossbauer and magnetization measurements were used to study FexCu1−x alloys prepared by ball-milling. The X-ray data show the formation of a nanocrystalline Fe—Cu solid solution. The samples with x ≥ 0.8 and x ≤ 0.5 exhibit bcc or fcc phase, respectively. Both the bcc and fcc phases are principally ferromagnetic for x ≥ 0.2, but the sample with x = 0.1 remains paramagnetic down to 78 K. The influence of the local environment on the hyperfine parameters and the local magnetic moment are discussed using calculations based on the discrete-variational method in the local density approximation.

Annealing Effect on the Structural and Magnetic Properties of Mn-Implanted 6H-SiC

n-type 6H-SiC(0001) substrates were implanted with a fluence of Mn+ 5× 1016 (maximum Mn content of 7%), with implantation energy of 80 keV and substrate temperature of 365 °C to promote recrystallization. The samples were characterized using Rutherford backscattering and channeling (RBS/C) spectroscopy and electron probe microanalysis in the energy dispersive X-ray (EPMA-EDX) technique; while the magnetization was studied using a superconducting quantum interference device techniques. In the as-implanted sample, three well-defined specific defect zones were identified as deduced from the analysis of RBS/C spectra. It is shown that the two main vacancy-related and interstitial-related defects undergo limited changes when annealing at 800 °C, while a major recovery is obtained after annealing at 1100 °C. Strain relaxation was also observed upon annealing as determined from HRXRD. Magnetization was strongly reduced with increasing annealing temperature from 800 °C to 1600 °C. This effect seems to be related to the dilution effect (reduction of Mn content) due to the local diffusion of Mn as suggested from the results obtained using both RBS/C and EPMA-EDX techniques.

Magnetic Structure of Mn-doped 6H-SiC

We investigated the local magnetic properties of Mn-doped 6H-SiC using ab-initio calculations. The calculation addresses various configurations of Mn single impurity and Mn dimers at substitutional/interstitial sites with and without neighboring Si and C vacancies. The calculations showed that a substitutional Mn atom at either Si or C sites possesses a magnetic moment. The Mn atom at Si site possesses larger magnetic moment than Mn atom at C site. Our calculations show that antiferromagnetically coupled pair of Mn atoms at Si sites with neighboring C vacancy is magnetically more stable. The calculation also showed that the interstitial sites with C neighbors are more favorable than those with Si and the magnetic moment for Mn at interstitial sites is less compared to that at substitutional sites. The results are used to understand the experimental data obtained on Mn- 6H-SiC for various Mn concentrations.

Effect of iron on vanadium (001) strained surface magnetism

The magnetism of the vanadium (001) surface has been a controversial subject on both theoretical and experiment fronts. Both strongly ferromagnetic and paramagnetic phases were reported. We have used the first principle full-potential linearized-augmented plane waves (FP-LAPW) as implemented in WIEN2k package to study the magnetic properties of strained surfaces of vanadium films as a function of film thickness. We found that for films thicker than about 11 monolayers, the magnetism of the strained surfaces converge to a constant value of about 0.15μB. Introduction of Fe monolayers and impurities at the centre of the films affects the magnetic structure of thin films but has no influence on the surface magnetism of thicker films. For Fe monolayers positioned at the centre of thick films, the Fe atoms maintain magnetic moment of order 0.86μB, a quadruple splitting of order -0.3 mm/s and a small negative isomer shift, while an Fe impurity has vanishing hyperfine fields and magnetic moment. In addition we have varied the location of the Fe monolayer and impurity within the V films and found that their position affects the surface magnetism.