Simulation of grain boundaries resistance in two-phase thin films of lanthanum manganites

Vytautas Petrauskas 1Evaldas E. Tornau 

1. Semiconductor Physics Institute, A.Gostauto 11, Vilnius LT-2600, Lithuania

Abstract

We present the model describing temperature and magnetic field dependences of grain boundary (GB) resistivity and magnetoresistivity of 2-phase epitaxial and/or polycrystalline films of lanthanum manganites. Assuming film thickness d dependence on concentration of both phases, we calculate by mean field approximation the magnetization of the 2-phase system and its dependence on d. Introducing the concept of grains, we obtain the difference in neighboring grains magnetization and link it to the GB resistivity by the phenomenological formulae. Characteristic features of temperature dependences of resistivity of lanthanum manganite films (peak of resistivity maximum Tm, difference of Tm and Curie temperature Tc, high resistivity of ultrathin films and shift of Tm with increasing d to higher temperature) might be found studying thus obtained GB resistivity. Our calculations show that, in order to obtain the peak at Tm, both grain boundary layers have to be, at least, weakly ferromagnetic. Increase of the ferromagneticity of these layers, leads to decrease of GB resistivity, increase of Tm and decrease of the difference between Tm and Tc. Increase in the number of grain boundaries also leads to decrease of GB resistivity. Our model allows to describe the difference observed in temperature dependences of resistivity for very thin (strained) films and thicker films with the electric and magnetic properties of the bulk systems.

 

Presentation: poster at E-MRS Fall Meeting 2005, Symposium F, by Vytautas Petrauskas
See On-line Journal of E-MRS Fall Meeting 2005

Submitted: 2005-05-21 07:47
Revised:   2009-06-07 00:44