Nanocomposites and nanomaterials

Ferromagnetic-piezoelectric composites for spin electronics
V.P. Sohatsky, Bialkivsky E.Y. , Dovbak M.V. 
T. Shevchenko National University of Kyiv, 60 Volodymyrska Str., 01601, Ukraine. 
E-mail: vso@univ.kiev.ua 

Composite nanostructures made of ferromagnetic and piezoelectric layers are promising for application in non-volatile memory, processors, magnetic field sensors, nanomechanical probes, etc. For various purposes, they were used as the ferromagnetic metal structures (Fe and/or NiFe nanolayers separated by nonmagnetic Cu sublayer) or non-conducting dielectrics (crystalline Y3Fe5O12), tightly bound with a piezoelectric - lead zirconate-titanate Pb[Zr0.52Ti0.48]O3. The most promising use of the second type structures is processing of the microwaves.
In this work, changes of magnetic properties of the above composites under mechanical and electrical influence were investigated. Physical mechanism of the observed early in our experiment “non-magnetic” changes of magnetization, was studied magnetooptically and by means of electrical and magnetic resonance methods. Simulation of remagnetization was performed on the basis of the energy balance equations taking into account the energies of the additional effects. The shape of the magnetization reversal curves (hysteresis loops), calculated on the basis of the traditional Stoner-Wolfart model with additional corrections for coercivity and changes in the exchange and magnetostatic components of magnetic energy when magnetization distribution changes, turned out to be quite close to those obtained experimentally. This confirms the possibility of using improved model to estimate magnetization not only at uniform distribution, but also in magnetically inhomogeneous media.
Transfer of the magnetic moment by current of polarized electrons in a ferromagnetic nanolayer can also be taken into account as an additional energy anisotropically distributed over the azimuth. Thus evaluation confirmed the possibility of maximal reducing of the threshold current of remagnetization by up to 3 orders of magnitude. This effect was previously observed with magneto-optical Kerr effect as a jump-like remagnetization of the layer with rectangular hysteresis loop and application of the external magnetic field, smaller than the field of remagnetization. 
Despite a simplicity of this model, it allows to predict the distribution of magnetization for specified parameters of studied media with a sufficient accuracy.