Room Temperature Tunable Multiferroic Properties in Sol-Gel-Derived Nanocrystalline Sr(Ti1-xFex)O3-δ Thin Films.

Yi-Guang Wang,Qiu-Xiang Liu,Yan-Ping Jiang,Xin-Gui Tang,Li-Li Jiang

doi:10.3390/nano7090264

Abstract

Sr(Ti1−xFex)O3−δ (0 ≤ x ≤ 0.2) thin films were grown on Si(100) substrates with LaNiO3 buffer-layer by a sol-gel process. Influence of Fe substitution concentration on the structural, ferroelectric, and magnetic properties, as well as the leakage current behaviors of the Sr(Ti1−xFex)O3−δ thin films, were investigated by using the X-ray diffractometer (XRD), atomic force microscopy (AFM), the ferroelectric test system, and the vibrating sample magnetometer (VSM). After substituting a small amount of Ti ion with Fe, highly enhanced ferroelectric properties were obtained successfully in SrTi0.9Ti0.1O3−δ thin films, with a double remanent polarization (2Pr) of 1.56, 1.95, and 9.14 μC·cm−2, respectively, for the samples were annealed in air, oxygen, and nitrogen atmospheres. The leakage current densities of the Fe-doped SrTiO3 thin films are about 10−6–10−5 A·cm−2 at an applied electric field of 100 kV·cm−1, and the conduction mechanism of the thin film capacitors with various Fe concentrations has been analyzed. The ferromagnetic properties of the Sr(Ti1−xFex)O3−δ thin films have been investigated, which can be correlated to the mixed valence ions and the effects of the grain boundary. The present results revealed the multiferroic nature of the Sr(Ti1−xFex)O3−δ thin films. The effect of the annealing environment on the room temperature magnetic and ferroelectric properties of Sr(Ti0.9Fe0.1)O3−δ thin films were also discussed in detail.

Highlights

Strontium titanate SrTiO3 has been widely applied in electronically tunable microwave devices for its high dielectric, low dielectric losses and high tunability [1,2]
A ferrodistortive phase transition temperature from cubic to tetragonal for SrTiO3 is as low as 105 K [5,6], which means the ferroelectric properties of the SrTiO3 are unavailable in most cases
The ferroelectric property has been obtained in the epitaxial SrTiO3 film [12] and the large epitaxial strain induced by the lattice mismatch

Summary

Introduction

Strontium titanate SrTiO3 has been widely applied in electronically tunable microwave devices for its high dielectric, low dielectric losses and high tunability [1,2]. In the low field regions, most thin films showed Ohmic conduction behavior, and the SCLC mechanism was observed in higher field regions This is because the SCLC will not be observed until the injected free-carrier density exceeds the volume-generated, free-carrier density [44]. After Fe substitution, oxygen vacancies were generated and the energy-band structure of STF was shaped with a reduced band-gap energy and reduction enthalpy, resulting in the increase of the free carriers in the films.

Materials and Methods

Findings

Conclusions