Manipulation of artificial multiferroics using doping-induced plastic strain relaxation

• Ferrimagnetic CoFe 2 O 4 was epitaxially grown on self-oxidized N-doped BaTiO 3 films. • N-doping of BaTiO 3 induces significant changes in growth mode and strain relaxation. • Relaxed CoFe 2 O 4 /N:BaTiO 3 shows enhanced magnetism and reduced magneto-crystalline anisotropy. In this work, we present a comprehensive and comparative study on the growth and magnetic properties of CoFe 2 O 4 layers deposited on both undoped and self-oxidized N-doped BaTiO 3 films grown on La 2/3 Sr 1/3 MnO 3 /SrTiO 3 (001) substrates, a prototypical magneto-electric multiferroic system. The oxide layers were grown by plasma-assisted molecular beam epitaxy. We show that N doping, even at a low level of 1 %, induces substantial changes in growth modes and strain relaxation in BaTiO 3 and consequently in the CoFe 2 O 4 top layer, which exhibits enhanced magnetization and reduced magnetocrystalline anisotropy. The magnetic properties were determined from extensive element-specific magnetic X-ray dichroic measurements, which were simulated through crystal field multiplet calculations. The structural properties of the samples were investigated using grazing incidence X-ray diffraction and high-resolution electron microscopy. Our observations provide evidence that the plastic relaxation of the underlying ferroelectric N-doped BaTiO 3 layer affects the magnetic properties of the top CoFe 2 O 4 layer and can serve as an additional tuning parameter for manipulating the expected properties of multiferroics.