Ferroelectric, electrical, and magnetic properties of BiFe_0.95Mn_0.05O₃ thin films epitaxially grown on conductive Nb:SrTiO₃ and La_0.7Sr_0.3MnO₃-buffered Nb:SrTiO₃ substrates

BiFe_0.95Mn_0.05O₃ (BFMO) thin films with different thicknesses have been epitaxially grown on <001>-oriented Nb-doped SrTiO₃ (NbSTO) and La_0.7Sr_0.3MnO₃(LSMO)-buffered NbSTO substrates by pulsed laser deposition. At high bias field the space-charge-limited current (SCLC) is the dominant conduction mechanism for all BFMO films while at low bias field the Ohmic conduction is the predominant mechanism. An analysis of leakage current characteristics reveals that the ferroelectric properties are critically dependent on the density of defects in BFMO films. For the BFMO/LSMO/NbSTO structure, the coercive field of the BFMO film is much smaller than that of the BFMO film directly grown on the NbSTO substrate, which is attributed to the suppression of the substrate-induced clamping effect. For both BFMO/NbSTO and BFMO/LSMO/NbSTO structures, the ferroelectric hysteresis loops show no change under a magnetic field up to 9 T, which is explained in terms of weak ferromagnetic-ferroelectric coupling in the BFMO film and the very low magnetic-field-induced electric voltage drop across the LSMO layer.