The origin of magnetism in perovskite ferroelectric ABO3 nanoparticles (A = K,Li; B = Ta,Nb or A = Ba,Sr,Pb; B = Ti)

Abstract

Using spin Hamiltonian models and Green’s function techniques, we study the ferroic order parameters of ferroelectric nanoparticles, and show how multiferroic behavior can be achieved in such systems. We present a theoretical study suggesting that unexpected ferromagnetic properties of perovskite ferroelectric ABO3 nanoparticles (A = K, Li; B = Ta, Nb or A = Ba, Sr, Pb; B = Ti) observed recently at room temperatures can be explained by considering oxygen vacancies at the surface of the nanocrystalline materials. Such vacancies lead to the appearance of Ta4+ and/or Ta3+ (Ti3+ and/or Ti2+) ions at the surface with nonzero net spin. The resulting different valence compared to the Ta5+ (or Ti4+) with S = 0 in the bulk offers a nonzero magnetization which increases with decreasing particle size. The system shows a multiferroic behavior below a critical size of the nanoparticles and the related polarization tends to a saturation value when the particle size is enhanced.

Carrier mediated ferromagnetism in Cr doped SrTiO3 compounds

“…Alkaline earth titanates ATiO 3 (A = Ca, Mg, Ba and Sr) have been investigated intensively for their technological applications in the field of capacitors, transducers and nonvolatile random access memory devices [3]. Among various ATiO 3 materials, SrTiO 3 system is one of the most investigated material due to their peculiar quantum paraelectric nature, semiconducting behaviour, in addition with it has been widely used in the field of pyroelectric detectors, electro optical modulators, thin film capacitors and optical memories [4]. SrTiO 3 also been used as a substrate material for superconducting cuprates and CMR materials [5].…”

Trends in (LaMnO3)n/(SrTiO3)m superlattices with varying layer thicknesses

“…A zoo of extraordinary phenomena, such as two dimensional quantum gases1, superconductivity2, magnetism3, magnetoresistance4, exchange bias56, half-metallicity7, and ferroelectricity8, is hosted by perovskite oxide heterostructures. The lattice, charge, orbital, and spin degrees of freedom and their competition give rise to these properties9.…”

Microstructure tuning and magnetism switching of ferroelectric barium titanate

“…7). Each oxygen vacancy is expected to donate two electrons to the empty d state of a single Ti 4+ ion to produce a Ti 2+ (d 2 ) ion with nonzero net spin (S = 1) or one electron each to two Ti 4+ ions, probably situated on either side of the oxygen vacancy, to make them Ti 3+ (d 1 ) ions with S = 1/2 [13]. Both configurations would result in the ferromagnetic ground state due to Hund's rule coupling [25].…”

“…BTO is one of the most extensively studied ABO 3 perovskite materials. In a previous theoretical study, Bahoosh et al have reported that oxygen vacancies can induce RT FM in nanosized BTO perovskite [13]. Compared with the nanopowders, high-performance nanolayered FE occupy more important position in the field of actual device preparations [14].…”