Mechanisms of anisotropy control by strain in FePt/BaTiO3

A. ROMÁN ; A. LOPEZ PEDROSO; A. LO GIUDICE; L. NEÑER; M. AGUIRRE; A. BUTERA; J. E. GÓMEZ; M. SIRENA; L.B. STEREN

Pittsburgh

Conferencia; MMM; 2017

 Nowadays, the design and fabrication of multiferroics (MF) is one of the main challenges for the development of oxidespintronics. Tuning the magnetic state of nanostructures by electric field orstrains appears to be the key for low-energy devices. Magneto-electric andmagneto-elastic coupling at interfaces between ferromagnetic (FM) andferroelectric (FE) layers are at the origin of these phenomena in artificialmultiferroics [1]. Both, the magnetic order and anisotropy of the FM componentcan be affected by the strains induced by the FM/FE lattice mismatch whilecharge transfer between both compounds can depend on the ferroelectricpolarization of the structure. A variety of FM and FE have been combined intoartificial MF, being the magnetic compounds generally oxides or transitionmetal alloys. In particular, FePt/BaTiO3 seems to be a very promising system.First-principle calculations revealed recently that important changes ofmagnetic anisotropy should be observed on the FePt overlayer when BaTiO3(BTO)is poled [2]. Moreover, the FePt disordered phase is a soft magnet  and  strongly sensitive to strains[3]. In this work we studied a series of FePt/BTO bilayers grown bysputtering on SrTiO3(100) substrates varying thickness from 20nm to 60nm. Thequality of the films has been probed by XRD, TEM and AFM measurements. Magneticcharacterization was done taking MFM images together with magnetization vs fieldcurves measured with a VSM at different temperatures. We observed an anomalousbehavior of the coercive field due to strains induced by the substrate and the FE(Fig 1). A stripe-type domain structure was observed on these structures abovea critical FePt thickness by MFM and reproduced using micromagnetic simulations(Fig 2).  The obtained results, both MFMand magnetometry ones,  are analyzed bytaking into account a  magneto-elastic couplingbetween the FE and the FM at interfaces. [1] C. A. Vaz, Journalof Physics: Condensed Matter, 24, 333201(2012).[2] M. Lee, H. Choi, Y.C. Chung, Journal of Applied Physics, 113, 17C729 (2013). [3] N. R. Alvarez, J. E. Gomez, A.E. MoyaRiffo, M.A. Vicente Alvarez, A. Butera, J. Appl. Phys. 119 1 (2016).