Defect driven ferroelectricity and magnetism in nanocrystalline KTaO3

TL;DR

This study demonstrates that defect-induced ferroelectricity and magnetism can be introduced in nanocrystalline KTaO3 through iron doping and oxygen vacancies, suggesting potential multiferroic behavior at low temperatures.

Contribution

It reveals the emergence of ferroelectric and magnetic orderings in nanocrystalline KTaO3 due to defects, a phenomenon absent in pure single crystals.

Findings

Defect-driven ferroelectricity and magnetism observed in nanocrystalline KTaO3.

Critical defect concentration decreases with particle size.

Potential for magnetoelectric effects below 29 K.

Abstract

Nominally pure nanocrystalline KTaO3 was thoroughly investigated by micro-Raman and magnetic resonance spectroscopic techniques. In all samples the defect driven ferroelectricity and magnetism are registered. Both ordering states are suggested to appear due to the iron atoms and oxygen vacancies. The concentration of defects was estimated to be 0.04 and 0.06-0.1 mole %, respectively. Note that undoped single crystals of KTaO3 are nonmagnetic and have never exhibited ferromagnetic properties. The results enable us to refer a nanosized KTa(Fe)O3 to the class of multiferroics and assume that it could perform the magnetoelectric effect at T<29 K. It was also established that the critical concentration of impurity defects necessary to provoke the appearance of the new phase states in the material strongly correlates with the size of the particle; as the size of the particle decreases, the critical concentration decreases as well.