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The acoustical spectral investigations of a ferromagnet Heusler Ni53Mn25Ga22 alloy crystal
|Yuri A. Kuzavko 1, Vasiliy D. Buchelnikov 2, V V. Koledov 3, Dmitriy A. Kostiuk 4, Vladimir V. Khovailo 3, Vladimir G. Shavrov 3
1. The Polesie Agrarian Ecological Institute of the National Academy of Science of Belarus (PAEI), Brest 224000, Belarus
Big attention is paid to materials with reversible form and size control by means of magnetic field, especially to Heusler Ni-Mn-Ga alloys (HA) with nonstechiometric composition, which are the highest achievement in this area allowing 6% of crystal size change.
That stimulated the undertaken research of longitudinal (LA) & transverse (TA) acoustic waves at their inclined fall in the (100) plane and reflection from the free border of a crystal (110), as far as from its border with liquid and dielectric. The ability of the temperature and magnetic field to effectively control the angles of reflection and transformation of wave types is shown.
There are investigated effects of a strong acoustic anisotropy and nonlinearity in Ni53Mn25Ga22 HA at region of martensitic, premartensitic and spin-orientational phase transitions (PT). The reflection & transition were numericaly examined for HA bondary with dielectric (liquid). The effect of full LA to TA transformation was registered as far as the appearance of accompanying surface oscillations and displacement up to cleavage of acoustical beams at the mediums bondary.
The existence of high harmonics (HG) at spread of LA & TA in solids is well-known, but their amplitudes are usually larger due to negligible elastic unharmonicity. HG measured in some crystalls were great acoustic nonlinearities. It takes place in Ni-Mn-Ga HA with giant magnetodeformation (up to 10%), coexisting with strong nonlinearity supplied martensitic and premartensitic PT.
Theoretical calculations were supported experimentally in polycrystalline Ni1.95Mn1.05Ga0.05 with 40oC PT temperature and Ni53Mn25Ga22 crystal with a coupled magnetostructural PT. Sound speeds at this crystal along , [1T0],  directions are subsequently vL=6.47 km/s, vL=6.91 km/s, and vL=5.71 km/s. The influence of reconstruction of structural variants & magnet domains may be caused by HG generation.
Authors are grateful to BRFFI and RFFI for support.
Presentation: Poster at E-MRS Fall Meeting 2008, Symposium C, by Yuri A. Kuzavko
See On-line Journal of E-MRS Fall Meeting 2008
Submitted: 2008-05-30 22:47 Revised: 2009-06-07 00:48