Supported by INTAS (International Association for the promotion of co-operation with scientists from the New Independent States of the former Soviet Union), 2002-2004
The main objectives of the project were the production of new spin-dependent semimagnetic semiconductor structures, the development of original experimental measuring techniques along with fundamental investigation of new spin-dependent phenomena for new spin electronic devices.
New important scientific results are reported in all 3 planned activities:
- Synthesis and growth of II-VI semimagnetic semiconductors in form of bulk crystals, thin films, multi-layer nanostructures and zero-dimensional structures (Activity I)
- Development of new experimental technique for study of spin-dependent phenomena in semimagnetic semiconductor crystals and nanostructures (Activity II)
- Exploration of spin-dependent phenomena in classical optoelectronic devices and new spin electronic schemes prototyping and testing (Activity III)
Summary of main results
1. Different single crystals of semimagnetic semiconductors (SMS) such as Cd1-xMnxTe, Zn1-xMnxO, Cd1-xDyxTe , Hg1-xEuxTe and CdTe crystals doped with different rare-earth elements Eu, Gd, Dy were successfully synthesized and investigated. Studies on their composition, temperature, magnetic field dependence of their magneto-optical effects. magneto-reflectance, Faraday rotation spectra and magnetoresistance were carried out. The giant Zeeman spin splitting of the exciton transition and the large Faraday rotation near the absorption edge in wide-gap SMS are interpreted in the framework of strong spin exchange interaction between electrons of magnetic ions and s, p band carriers.
2. Magnetotransport measurements for narrow-gap Hg1-xEuxTe with x = 0.05 have shown up to 70% magnetoresistance variation “R/R at room temperature. Strong temperature dependence of the “R/R below 200 K is attributed to the s, p f exchange interaction in SMS with the rare earth magnetic component.
3. Pulsed laser ablation technique was used for deposition of thin film and multilayer structures as well as for the fabrication of zero-dimensional structures (quantum dots). Superlattices of CdTe/Cd1-xMnxTe were deposited and investigated by several new techniques, such as time-resolved Faraday rotation in a wide temperature range (4.2 300) K. Light pumping induced magnetization in CdTe/CdMnTe quantum well structures was recorded.
4. Two key aspects for spin electronics were experimentally studied, namely: injection of spin-polarized carriers and detection of the injected carriers. New schemes for injection of spin-polarized electrons and magneto-optical detection by using Faraday rotation technique have been developed. External magnetic field and voltage were applied across the structures. The Faraday rotation angles were measured when electric field was switched on and off across heterostructure. The observed difference in the Faraday rotation angle for these two cases clearly demonstrates the effective injection of spin-polarized carriers from SMS into nonmagnetic semiconductor.
5. The rare-earth based SMS Hg1-xEuxTe which demonstrated large value of DR/R have been used as sensing elements for development of magnetic field sensors. Devices were made with multiple rectangular elements connected in series. In order to reduce the size, thin films of Hg1-xEuxTe were deposited on sapphire substrate by pulse laser ablation and tested for magnetoresistive sensors.
6. Magnetophotoluminescence experiments were carried out using Cd1-xMnxTe/CdTe structures at T = 5 K. To realise the injection of spins from Cd1-xMnxTe layers we excited the luminescence using He-Ne and Ar lasers. The photoluminescence of the Cd1-xMnxTe layers exhibited a 100 % degree of polarization which proves the fast spin alignment of the carriers into a spin aligner layers (this is a layer, which can be used for orientation of spins of carriers before injection into another structure).
7. A spintronic type of filter based on Cd1-xMnxS and Cd1-xMnxSe nanocrystals embedded in a polymer matrix has been developed. The functionality of such spintronic devices were demonstrated by using thin film containing paramagnetic nanocrystallites as an interface between ferromagnetic metal Co and nonmagnetic semiconductor CdSe. It was shown that such a structure Co/CdMnSe-nc/CdSe has influence on the spin injection which is similar to tunnel junction and is controlled by the voltage across the nanocrystallites.
8. Thin film multi-layer magnetic structures were deposited and optimised for various low noise magnetic field sensors. Original bridge schemes have been tested for anisotropic magnetoresitive sensors. Double layer magnetoresitive sensors have shown decreased hysteresis compared with known single layer sensors. Deposited spin-dependent structures with antiferromagnetic fixing layer of Fe50Mn50 have demonstrated 30 % magnetoresistive effect.
9. In order to implement a magnetic field effect transistor (MFET) a scheme was chosen in which an external magnetic field instead of the traditional electric field controls the current output. The design of MFET is based on a heterostructure with a p-n junction. Variation of the current was obtained when an external magnetic field of B = 2.5 T was applied along the p-n junction.
10. A new magnetometer, which we named “flux-spin magnetometer has been developed. Conditions for simultaneous measurement of three orthogonal magnetic field components by a single crystal film have been established. Theoretical analysis was developed to account for the intrinsic noise of the magnetic material and that of the coils. We suggested a way to design a magnetometer with a noise of several fT Hz 1/2 at room temperature. A prototype of a 3-D magnetometer was experimentally tested, achieving a detection level below 1 pT Hz 1/2 at frequencies above 0.1 Hz. It looks feasible to reach at room temperature the detection level of cooled SQUIDs.
Coordinator: Dr. Adrian Podoleanu, University of Kent at Canterbury, School of Physical Sciences, Applied Optics Group;
Partners: Professor Alessio Perrone, University of Lecce, Department of Physics, Laboratory of Radiation Physics, Via Arnesano, 73100, Lecce, Italy; Dr. Petr Ivanovich Nikitin, General Physics Institute of the RAS, Natural Science Research Centre, Low-Temperature Laser Plasma Laboratory, Vavilov Street, 38, 119991, Moscow, Russia;
Prof. Andriy Iosipovich Savchuk, Chernivtsi National University, Department of Physical Electronics and Nontraditional Energetics, Kotsyubinsky Street 2, 274012, Chernivtsi, Ukraine.
List of related publications
1. A.I.Savchuk, S.Yu.Paranchych, M.V.Kurganetski, I.D.Stolyarchuk, Yu.V.Tanasyuk, A. Perrone, M.L. DeGiorgi. Spin and Size Dependent Effects in Semimagnetic Semiconductor Nanostructures. Material Science and Engineering, 2003, vol. C 23, No.1-2, pp.259-262.
2. A.I. Savchuk, P.P. Vatamanyuk, V.I. Fediv, P.I. Nikitin, A. Perrone. Magneto-optical Study of Diluted Magnetic Semiconductor Nanostructures Prepared by Pulsed Laser Deposition. Journal of Superconductivity: Incorporating Novel Magnetism, 2003, vol 16, No.2, pp. 465-468.
3. A.I.Savchuk, P.N.Gorley, V.V.Khomyak, A.G.Voloshchuk, V.I.Fediv, S.V. Bilichuk, I.D.Stolyarchuk, A. Perrone. Synthesis and characterization of semimagnetic semiconductor nanocrystals for spin electronics. Material Science and Engineering, 2003, vol. C 23, pp.753- 756.
4. A.I.Savchuk, P.N.Gorley, V.V.Khomyak, K.S. Ulyanytsky, S.V. Bilichuk, A. Perrone, P.I.Nikitin. ZnO-based semimagnetic semiconductors: growth and magnetism aspects. Material Science and Engineering, 2004, vol. B 109, pp.196- 199.
5. A.I. Savchuk, V.I. Fediv, Ye.O.Kandyba, T.A.Savchuk, D.V.Ivanchenko, A. Perrone. A Comparative Study of Pure and Doped with Paramagnetic Impurities Semiconductor Nanocrystals. Material Science and Engineering C, 2004 (in press).
6. A.I. Savchuk, S.Yu. Paranchych, P.P.Vatamanyuk, V.I.Fediv, M.D. Andriychuk, Yu.V. Tanasyuk, P.I. Nikitin, Magneto-Optical and Magnetoresistance Effects in Semimagnetic Semiconductors Containing Rare Earth Ions. Paper H38 in Proceedings V2 of the 26th International Conference on the Physics of Semiconductors, Edinburgh,29 July August 2002, Series:Institute of Physics Conference Series Number 171 , Edited by:A R Long and J H Davies, Publisher:Institute of Physics Publishing, Place of publication:Bristol (UK)and Philadelphia (USA), Year of publication:2003, ISBN:-7503-0924-5
7. A.I.Savchuk, S.Yu.Paranchych, V.M.Frasunyak, V.I. Fediv, Yu.V.Tanasyuk, Ye.O.Kandyba, P.I.Nikitin. Optical and magnetooptical study of CdTe crystals doped with rare earth ions. Material Science and Engineering, 2003, vol. B 105, No.1-3, pp.161-164.
8. P.I. Nikitin, S.I. Kasatkin, A.M. Muravjov, P.M. Vetoshko, M.V. Valeiko, V.I. Konov, T. Meydan. Magnetic field sensors based on thin film multi-layer structures. Sensors and Actuators A, Vol 106/1-3 pp 26-29, 2003.
9. P. M. Vetoshko, M.V.Valeiko P.I. Nikitin, Epitaxial iron garnet film as an active medium of an even-harmonic magnetic field transducer. Sensors and Actuators A, Vol 106/1-3 pp 270-273, 2003.