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Acoustic Spectrum of Nanoparticles of a Heysler Shape Memory Ferromagnetic Alloy

Yuri A. Kuzavko 

The Polesie Agrarian Ecological Institute of the National Academy of Science of Belarus (PAEI), Brest 224000, Belarus

Abstract
Nanofilms of Heysler Ni2+x+y Mn1-x Ga1-y shape memory alloy received by methods of laser and magnetrone spray or molecular-beam epitaxy have differences in comparison with specimen of the same stechiometric constitution: they have lower phase transition temperatures and magnetic moments. Obvious features of ferromagnetic nanoparticles are big surface to volume ratio and limited amount of atoms. Difference of a surface power constants from their values inside the infinite crystal (that is due to non-compensated powers on the free surface) leads to a grid deformations, appearance of surface tension and localized surface waves, as far as to strong anharmonism. Sizes of an elementary crystallographic cell a=0,5825 nm for room temperature and a=b=0,5920 nm, c=0,5566 nm at for low temperatures for Ni2MnGa.

Photonic spectrum of Heysler alloy nanoparticles in austenite phase was received from the frequency spectrum infinite crystal, taking into account the Einstein model of a solid body, atomic-sphere approximation and contribution of the particle surface. While N increases, nanoparticle photonic spectrum quickly comes close to an oscillation spectrum of an infinite crystal. Numeric estimate of the maximum critical diameter of the Ni2MnGa one-domain nanoparticle makes Dc approximately equal to 50 nm. Particles with sizes bigger than d=4 nm are owning ferromagnetism. There is no shape memory effect in one-domain nanoparticles.

Author is grateful for BRFFI-RFFI F04R-080 grant for partial financial support

 

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Presentation: Poster at E-MRS Fall Meeting 2007, Acta Materialia Gold Medal Workshop, by Yuri A. Kuzavko
See On-line Journal of E-MRS Fall Meeting 2007

Submitted: 2007-05-14 23:05
Revised:   2009-06-07 00:44