Magnetic polaron percolation on a rutile lattice: A geometrical exploration in the limit of low density of magnetic impurities

Sangaletti, L.; Canova, F. Federici; Drera, Giovanni; Salvinelli, Gabriele; Mozzati, Maria Cristina; Galinetto, P.; Speghini, Adolfo; Bettinelli, Marco

doi:10.1103/physrevb.80.033201

Cited by 7 publications

(13 citation statements)

References 18 publications

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“…Magnetization saturation value M S depends on the magnetic moments of oxygen vacancies V(O) and Fe 3+ ions and their amounts N 1 and N 2 , respectively, in the infinite cluster as M S = | S 1 N 1 − S 2 N 2 |, that is in a complete agreement with Ref. [20]. …”

Section: Discussionsupporting

confidence: 89%

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Percolation Magnetism in Ferroelectric Nanoparticles

2017

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Nanoparticles of potassium tantalate (KTaO3) and potassium niobate (KNbO3) were synthesized by oxidation of metallic tantalum in molten potassium nitrate with the addition of potassium hydroxide. Magnetization curves obtained on these ferroelectric nanoparticles exhibit a weak ferromagnetism, while these compounds are nonmagnetic in a bulk. The experimental data are used as a start point for theoretical calculations. We consider a microscopic mechanism that leads to the emerging of a ferromagnetic ordering in ferroelectric nanoparticles. Our approach is based on the percolation of magnetic polarons assuming the dominant role of the oxygen vacancies. It describes the formation of surface magnetic polarons, in which an exchange interaction between electrons trapped in oxygen vacancies is mediated by magnetic impurity Fe3+ ions. The dependences of percolation radius on concentration of the oxygen vacancies and magnetic defects are determined in the framework of percolation theory.

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Section: Discussionsupporting

confidence: 89%

“…Here, M S is the saturation magnetization, H is a static magnetic field, and V 0 is the volume of infinite (in fact, closured over a nanoparticle surface) magnetic cluster. Saturation magnetization was defined in accordance with the formula (7) from [ 20 ]: …”

Section: Introductionmentioning

confidence: 99%

Percolation Magnetism in Ferroelectric Nanoparticles

2017

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“…At the same time the important role played by the defect concentration in determining the magnetic properties became evident, making them strongly dependent on the preparation technique and intrinsic disorder 8. Among the possible models the bound magnetic polarons (BMPs) model, has received great attention in recent years 7–15. The basic idea is the polarization of TM ion spins by a localized defect.…”

Section: Introductionmentioning

confidence: 99%

“…For low TM concentrations or even for undoped material this model is hardly usable due to the small number of transition ions in the polaron sphere. The contribution of the defect itself has to be considered 11, 12, 15. Therefore, any information about magnetic ion and/or defect states, obtained with specific experimental methods, is very valuable.…”

Section: Introductionmentioning

confidence: 99%

Spin dynamics in ⁵⁷Fe‐doped TiO₂ anatase nanoparticles

Grecu

Constantinescu

Tărăbăşanu-Mihăilă

et al. 2011

Physica Status Solidi (b)

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In this paper we present electron paramagnetic resonance (EPR) and Mössbauer (transmission method, TMS and measurements in the scattering method, CEMS) experiments on 57 Fe (0.1-1 at.%) doped nanocrystalline anatase-type TiO 2 , synthesized by a hydrothermal method. Different Fe 3þ and Fe 2þ ions positions, with various hyperfine interactions evidenced in Mössbauer spectra (MS), confirm a partial magnetic ordering at room temperature. The magnetic hyperfine fields in the TMS spectra, better resolved at lower temperatures, do not change essentially with temperature. The first CEMS measurements, carried out on iron-doped TiO 2 nanoparticles, reveal a larger disorder in the surface particles layer. The temperature dependence of the double integral EPR spectral intensity, proportional with the sample susceptibility, shows an anomalous behaviour. It suggests the bound magnetic polaron (BMP) mechanism for the magnetic ordering.

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“…It is often assumed (see, e.g., refs. ) that the localized carriers created with an oxygen vacancy can be described by a wavefunction such as

Ψ true(r true) = {true(π {a_{B^{}}}^{3} true)}^{- 1 / 2} \exp true(- r / a_{B} true)

where a B can be regarded as a polaron radius and the interaction between localized carriers (and their spin) can be discussed in the frame of polaron percolation theory. In particular, in the anatase‐type lattice, assuming a first nearest neighbor (NN) cation–cation interaction, the percolation occurs when 27.9% of Ti atoms have a magnetic moment .…”

Section: Resultsmentioning

confidence: 99%

Effects of Nearly‐2D Oxygen Vacancy Clustering on the Magnetic Properties of d⁰ Systems: The Case of Anatase and Rutile TiO₂

Drera

Mozzati

Malavasi

et al. 2018

Physica Status Solidi (b)

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A comprehensive magnetic characterization in a set of rutile and anatase thin films grown on different substrates is reported. TiO 2Àδ films have been grown with the RF-sputtering technique on various non-magnetic substrates (fused silica, Al 2 O 3 , LSAT); subsequently, a protocol of annealing procedures has been applied in order to alter the sample oxygen stoichiometry. Magnetic characterization has been carried out at each step of the films treatments. It is shown that control over oxygen stoichiometry can be used in these samples to induce room-temperature ferromagnetism (FM). Percolation schemes developed for the anatase or rutile lattices are considered to show that FM is related to clustered oxygen vacancies. The values of saturation magnetization, determined from thin films in a wide thickness range (33-317 nm), indicate that ferromagnetic ordering can be explained on the basis of a magnetic layer hosting a percolating cluster related to oxygen vacancies at the interface with the substrate or at the film surface, the first being common to all samples, while the second being triggered by vacuum annealing.

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Magnetic polaron percolation on a rutile lattice: A geometrical exploration in the limit of low density of magnetic impurities

Cited by 7 publications

References 18 publications

Percolation Magnetism in Ferroelectric Nanoparticles

Percolation Magnetism in Ferroelectric Nanoparticles

Spin dynamics in ⁵⁷Fe‐doped TiO₂ anatase nanoparticles

Effects of Nearly‐2D Oxygen Vacancy Clustering on the Magnetic Properties of d⁰ Systems: The Case of Anatase and Rutile TiO₂

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Magnetic polaron percolation on a rutile lattice: A geometrical exploration in the limit of low density of magnetic impurities

Cited by 7 publications

References 18 publications

Percolation Magnetism in Ferroelectric Nanoparticles

Percolation Magnetism in Ferroelectric Nanoparticles

Spin dynamics in 57Fe‐doped TiO2 anatase nanoparticles

Effects of Nearly‐2D Oxygen Vacancy Clustering on the Magnetic Properties of d0 Systems: The Case of Anatase and Rutile TiO2

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Product

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Spin dynamics in ⁵⁷Fe‐doped TiO₂ anatase nanoparticles

Effects of Nearly‐2D Oxygen Vacancy Clustering on the Magnetic Properties of d⁰ Systems: The Case of Anatase and Rutile TiO₂