- Department - UNREGISTERED VERSION

FUNCTIONAL MATERIALS GROUP

The group studies smart materials with functional properties: magnetic shape memory, shape memory, magnetoelastic, giant magnetostriction, unusual thermal expansion. The main scientific interest is fundamental study of the magnetic shape memory and its thermal-, mechanical- and times stability. The goal is to develop physical principles for design of new magnetic shape memory materials. Studies are focuswd on clarification of correlation between the alloy compositions, phase transformation temperatures, crystalline, magnetic and electronic structures and occurrence of magnetic shape memory using the complex experimental methods and theoretical analysis.


Main scientific results in the field of Magnetic Shape Memory:

• Giant MSME of 5% due to rotation of the magnetic field is obtained under low magnetic field value (H=0,25-0,4T) at room temperature in nonstoichiometric Ni2MnGa (2000).
  

• Reversible strain up to 3% was obtained in the magnetic field and compressive stress applied together in the orthogonal directions at room temperature, which is a real model for actuating element (2000).
  

• New physical phenomenon- magnetic creep is found in nonstoichiometric magnetic shape memory Ni2MnGa: the time-dependent evolution of the martensitic structure and field-induced strain under steady magnetic field and constant temperature. An analogy between a magnetic creep and mechanical creep is found in ferromagnetic martensities of Ni2MnGa. Dependence kinetics of the magnetic creep on the external magnetic field direction and on the magnetic field value is found (2000-2002).
  

• Temperature stability of martensite and magnetic-field-induced strain with cooling was studied. Firstly is found a rise of martensite tetragonality with cooling, which strongly affects the magnetic field induced strain (2001-2002).
  

• Crystalline structure of martensite in the alloy showing giant MFIS of 5% was clarified with X-ray and neutron diffraction within the whole temperature interval from Ms=302 K (start of martensite transformation) temperature down to 4K.
  

• Redistribution of twin martensitic domains studied in-situ within the temperature range 302 K-99 K. Effect of temperature on the magnetic field value needed for activating of strain is clarified within temperature range 302 K- 160K (2002).
  

• New way for shape memory in ferromagnetic Ni-Mn-Ga alloys is found:  fully reversible magneto-thermal shape memory effect (2002).
  

• Strong anisotropy and large negative thermal expansion up to -2% is found within temperature range 340-4K in off stoichiometric Ni-Mn-Ga compound (2002).
  

• Crystallography of twinning for the combined twins system is determined for the 5-layered modulated monoclinic structure of martensite in the nonstoichiometric magnetic shape memory Ni-Mn-Ga (2003).
  

International cooperation:

(i)       Helsinki University of Technology, Laboratory of Physical Metallurgy and Materials Science, Espoo, Finland (Prof. V. K. Lindroos);
(ii)      Hahn-Meitner-Institut, BENSC, Berlin, Germany (Dr. R. Shnaider);
(iii)     European Office of Aerospace Research & Development. London,UK (Dr.Ch. Ward).

Projects:
High temperature magnetic shape memory Ni-Mn-Ga alloys for a new class of actuators and sensors (STCU P137).
Partner- European Office of Aerospace Research & Development (EOARD). Supported by European Office of Aerospace Research & Development. London. UK

GROUP MEMBERS

• Glavatska Nadiya, team leader
  

• Mogylna Iryna
  

• Musienko Denys