Unravelling the effect of SrTiO3 antiferrodistortive phase transition on the magnetic properties of La0.7Sr0.3MnO3 thin films


Epitaxial La0.7Sr0.3MnO3 (LSMO) thin films, with different thicknesses ranging from 20 to 330 nm, were deposited on (1 0 0)-oriented strontium titanate (STO) substrates by pulsed laser deposition, with their structure and morphology characterized at room temperature. The magnetic and electric transport properties of the as-processed thin films reveal an abnormal behaviour in the temperature dependent magnetization M(T) below the antiferrodistortive STO phase transition (T-STO), and also an anomaly in the magnetoresistance and electrical resistivity close to the same temperature. Films with thickness <= 100 nm show an in-excess magnetization and pronounced changes in the coercivity due to the interface-mediated magnetoelastic coupling with antiferrodistortive domain wall movement occurring below T-STO. However, in thicker LSMO thin films, an in-defect magnetization is observed. This reversed behaviour can be understood with the emergence in the upper layer of the film, of a columnar structure needed to relax the elastic energy stored in the film, which leads to randomly oriented magnetic domain reconstructions. For enough high-applied magnetic fields, as thermodynamic equilibrium is reached, a full suppression of the anomalous magnetization occurs, wherein the temperature dependence of the magnetization starts to follow the expected Brillouin behaviour.






Mota, DA; Barcelay, YR; Senos, AMR; Fernandes, CM; Tavares, PB; Gomes, IT; Sa, P; Fernandes, L; Almeida, BG; Figueiras, F; Vaghefi, PM; Amaral, VS; Almeida, A; de la Cruz, JP; Moreira, JA

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This work was supported by the Fundacao para a Ciencia e Tecnologia and COMPETE/QREN/EU, through the project PTDC/CTM/099415/2008. The authors are very grateful to Maria Joao Pereira and Maria Rosario Soares from CICECO, University of Aveiro, for the HR-XRD measurements and discussion of the results. F Figueiras acknowledges FCT grant SFRH/BPD/80663/2011. The authors also acknowledge Projeto Norte-070124-FEDER-000070 and Professor J Fontcuberta for their fruitful discussions.

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