SQUID Magnetometer
The SQUID magnetometer (MPMS XL 5, Quantum Design) - a device measuring the strength of the magnetic moment produced by a magnetised sample with sensitivity of 10-11 Am2. The device allows measurements in the fields up to 5 T and in the temperature range of 1.9-400 K. The measurements can be performed in the DC and AC modes. The set-up also includes vertical and horizontal sample rotators, external device control, manual insertion utility probe (allowing a variety of transport measurements), magnet reset and nitrogen jacketed dewar. The system is traceable to standards of the magnetic field and moment. The magnetometer is open for commercial exploitation.
1. Single-crystalline Ge1-x Mnx nanowires
Magnetically doped Si and Ge nanowires have potential application in future nanowire spin-based devices. We used a supercritical fluid method for producing single crystalline Mn-doped Ge nanowires, with a Mn concentration of 0.5-1.0 atomic %, that display ferromagnetism above 300 K and a superior performance with respect to the hole mobility of around 340 cm2/Vs, demonstrating the potential of using these nanowires as building blocks for electronic devices [1]. The work is a result of close collaboration with scientists in Ireland (UCC and Trinity College) and USA (Intel Corporation and University of California).
2. Effects of dimensionality on magnetic properties of group-IV semiconductors
Effects of dimensionality on magnetic and electric properties of one- and two-dimensional GeMn systems and the role of defects in magnetic ordering are investigated by means of Electron Spin Resonance (ESR) and SQUID magnetometry techniques. We show an excellent correlation between these two experimental techniques, as it is demonstrated by the temperature dependencies of the magnetic moment and susceptibility [2]. In particular, it was shown that Ge1-xMnx nanowires could be characterised by a perfect dilution of Mn ions and high operating temperature, making them attractive for spintronic applications [3]. This study emphasises the important role of dimensionality as well as of the type and distribution of magnetic defects in spin-dependent scattering and dynamic magnetic properties of diluted magnetic semiconductors. The work is done in collaboration with scientists in Russia (IPCP RAS), Germany (Duisburg Univ.) and Italy (Univ. of L'Aquila).
3. Unusual magnetism of NiS nanoparticles
For the first time we observe unusual magnetic properties of NiS nanoparticles which potentially have a high industrial impact. Metal sulfides can have considerable advantages compared to metals and oxides combining mechanical and thermal robustness with additional chemical stability particularly in hydrothermal conditions. The magnetic properties of the spinel ferrimagnetic semiconductors and mineral phases have attracted interest for a number of device technologies. We investigate a nanoscale sulfide system, NiS, which demonstrates high temperature ferromagnetism together with low temperature superparamagnetism and associated blocking and spin-glass effects. Our results suggest that NiS may have technological importance as a ferromagnetic semiconductor. The work is done in collaboration with UCC, Ireland.
References
[1] M. I. van der Meulen, et al. Single Crystalline Ge1-xMnx Nanowires as Building Blocks for Nanoelectronics. Nano Lett., 9, 50 (2009).
[2] O. Kazakova, et al. Effect of dimensionality on the spin dynamics of GeMn systems: Electron spin resonance measurements. Phys. Rev. B, 77, 235317 (2008).
[3] O. Kazakova, et al. Room Temperature Ferromagnetism in Ge1-xMnx nanowires. Phys. Rev. B. 72, 0944415 (2005).