Thickness dependence of the magnetoelectric coupling in FeGa thin films deposite don PMN-PT single crystals

JIMÉNEZ, M. J.; GÓMEZ, J.E.; VELÁZQUEZ RODRIGUEZ, D.; LEIVA, L.; MILANO, J.; BUTERA, A.

San Martín, Buenos Aires

Encuentro; XIX Encuentro de Superficies y Materiales Nanoestructurados. Nano 2019; 2019

CNEA, INN e INTI

Straintronics have recently emerged as an alternative for ultra low power switching of magnetic nanoelements in storage devices.[1] The magnetization of small elements can be rotated, or even switched, when they are grown on top of a piezoelectric layer that can be deformed with the application of a relatively small voltage.[2] The voltage is applied on the top and bottom faces of the piezoelectric (PE) material that deforms anisotropically and induces a change in the easy axis of magnetization of the ferromagnet (FM) via the inverse magneostrictive effect. Several different materials have been proposed and used for the ferromagnetic and piezolectric components,[3] and, as a general rule to obtain a large magnetoelectric effect, the FM should have a high magnetostriction constant and the PE a large piezoelectric coefficient.We have investigated the effects of applying an electric field on the dc and ac magnetic response of FeGa thin films (t=6, 11, 17, 22, and 28 nm) that have been deposited on ferroelectric PMN-PT [011] and [001] single crystals.Upon the application of an electric field we have observed that M vs. H hysteresis loops are modified in films grown on [011] crystals, consistent with a negative magnetostriction constant that depends on film thickness. Samples deposited on [001] substrates, on the other hand, show a very weak dependence on thickness with electric field.Ferromagnetic resonance experiments at 9.5 GHz were performed in order to estimate the magnetostriction constant and to obtain the magnetoelectric coefficient as a function of thickness. We have observed that in the case of [011] substrates the magnetostriction constant depends on film thickness and has relative maxima for t=6 and 28 nm. The magnetoelectric coefficient shows a similar dependence on film thickness, confirming that the main effect is due to magnetoelastic anisotropy. In the case of 28 nm films deposited on PMN-PT [011] it was found that the direction of easy magnetization could be rotated by 90º upon the application of an electric field.These results indicate that if magnetostrictive materials are to be applied in straintronic devices the dependence of magnetic parameters with film thickness must be taken in account for optimum performance.