Double Perovskite Sr2FeMoO6: A Potential Candidate for Room Temperature Magnetoresistance Device Applications

The family of double perovskites first received attention in the 1960s, but the discovery of low field magnetoresistnace (LFMR) and half metallicity of the Sr2FeMoO6 (SFMO) compound was made by Kobayashi et al. in 1998. A fully spin polarized half-metal SFMO (Tc > 400) with excellent magnetoresistance response relatively at small applied fields and high temperatures makes SFMO an ideal candidate for room temperature spintronics applications. Primarily, most of the research work on double perovskites SFMO has been focused on bulk ceramic samples and aimed to understand their structural, magnetic, and magnetotransport properties, along with correlation among them. A material such as SFMO that exhibits a large decrease in resistivity and magnetically order well above room temperature is necessary for the advancement of spintronic devices. If the bulk properties observed could be reproduced in thin films, industrially produced SFMO-based spintronic devices could become a reality. Therefore, the purpose of this chapter is to present the detailed background and descriptions of the double perovskite Sr2FeMoO6 (SFMO) thin films and heterostructures with main emphasis to improve or achieve room temperature magnetoresistance properties especially for room temperature magnetoresistive device applications

Struktur und Magnetotransport laserdeponierter Lanthanmanganat Dünnschichtsysteme

Die vorliegende Dissertation "Struktur und Magnetotransport laserdeponierter Lanthanmanganat Dünnschichtsysteme" beschäftigt sich mit der Herstellung, den strukturellen Eigenschaften und dem Magnetotransport von ferromagnetisch-metallischen Lanthanmanganat-Schichten La0.7A0.3MnO3 (A=Sr, Ca) und Schichtsystemen. Die untersuchten Schichten und Schichtsysteme wurden mittels Laserablation in "off-axis" Geometrie auf einkristallinen oxidischen Substraten abgeschieden. An einer Serie von polykristallinen La0.7Sr0.3MnO3/Y:ZrO2(100) Schichten wurde der Korngrenzen-Magnetowiderstandseffekt ferromagnetisch-metallischer Manganate untersucht. Durch Variation der Substrattemperatur während der Abscheidung läßt sich die Textur graduell einstellen. Untersuchungen des quantitativen Verhaltens des Magnetowiderstandes zeigen eine klare Korrelation des Niederfeld-Magnetowiderstandes und des Hochfeld-Magnetowiderstandes. Durch Untersuchungen an einer nichttexturierten Schicht in hohen gepulsten Magnetfeldern konnte auf einen indirekten Tunnelprozeß der Elektronen durch die Korngrenze entsprechend einem Modell von Lee et al. geschlossen werden, wobei die magnetische Ordnung der Korngrenze antiferromagnetisch ist. An den epitaktischen Schichtserien La0.7Ca0.3MnO3/NdGaO3(110) und La0.7Sr0.3MnO3/SrTiO3(100) und an heteroepitaktischen Multilagen (La0.7Sr0.3MnO3/SrTiO3)n/SrTiO3(100) wurden die strukturellen, magnetischen und elektrische Eigenschaften in Abhängigkeit von der Schichtdicke und der Einfluß der Grenzflächeneigenschaften untersucht. Allgemein zeigte sich, daß die mechanische Verspannung und Mikrostruktur der Schichten einen großen Einfluß auf deren physikalischen Eigenschaften haben. Die beobachtete Reduzierung der Curie-Temperatur, der Metall-Isolator-Übergangstemperatur und der spontanen Magnetisierung kann auf den finite-size Effekt und auf die Ausbildung von Perkolationspfaden (metallische Cluster in nichtmetallischer Matrix) in den ultradünnen Schichen zurückgeführt werden

Impact of Alkali Ions Codoping on Magnetic Properties of La(0.9)A(0.1)Mn(0.9)Co(0.1)O(3) (A: Li, K, Na) Powders and Ceramics

The aim of the work was to check how the introduction of alkali and cobalt ions into a manganese structure can affect the structural disorder and, in consequence, lead to the changes (improvements) of magnetic properties. The high-pressure sintering technique was applied to check if the external factor can modify the magnetization of manganites. Nanocrystalline La0.9A0.1Mn0.9Co0.1O3 (where A is Li, K, Na) powders were synthesized by the combustion technique. The respective powders were used for nanoceramics preparation by the high-pressure sintering technique. The structure and morphology of the compounds were studied by X-ray powder diffraction, scanning electron microscopy and energy-dispersive X-ray spectroscopy. Magnetization studies for all compounds were performed in order to check the changes induced by either codoping or the sintering pressure. It was found that the type of the dopant ion and sintering pressure produced significant changes to the magnetic properties of the studied compounds. Alkali ions lead to the stabilization of Co ions in the +2 oxidation state and the formation of positive exchange interactions Mn3+–Mn4+ and Co2+–Mn4+ and the subsequent increase in remanent magnetization. High sintering pressure leads to a decrease in grain size and reduction of long-range ferromagnetic order and lower magnetization. © 2020 by the authors. Licensee MDPI, Basel, Switzerland.This project has received funding from the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska‐Curie grant agreement No 778070–TransFerr–H2020‐MSCA‐RISE‐ 2017. Part of this work was developed within the scope of the project CICECO‐Aveiro Institute of Materials, UIDB/50011/2020 and UIDP/50011/2020, financed by national funds through the Portuguese Foundation for Science and Technology/MCTES. The equipment of the Ural Center for Shared Use “Modern nanotechnology” UrFU was used. The work has been supported in part by the Ministry of Science and Higher Education of the Russian Federation under Project № FEUZ‐2020‐0054

Coupling of strain and magnetism in manganite-based complex oxide heterostructures

Complex oxide thin films and heterostructures offer a wide range of properties originating from the intrinsic coupling between lattice strain and magnetic/electronic ordering. This article reviews experimental, phenomenological, and theoretical analyses of the coupling of strain with electronic and magnetic properties of mixed valence manganite heterostructures. The influence of epitaxial strain on the magnetic properties of manganite films is measured using macroscopic magnetization measurements and shown mixed reports suggesting, both, an increase and decrease in ferromagnetic phases on the application of the strain. Using polarized neutron reflectivity (PNR), a simultaneous measurement of transport and magnetic properties of manganite thin films showed direct evidence of modification in the magnetic properties on the application of bending strain. The coupling coefficient of strain and magnetism of manganite heterostructures was estimated using PNR, which not only helped to understand the correlation of elastic strain with magnetism but also explained the condition of magnetic phase order change in the phase-separated systems within a phenomenological Ginzburg Landau theory. An overview is also provided of the current perspectives and existing studies on the influence of strain on structure, electronic, magnetic, magnetic anisotropy, phase coexistence and magnetocaloric properties of mixed valence manganite heterostructures. Based on the understanding of a diverse range of perovskite functionalities, detailed perspectives on how the coupling of strain and magnetism open up pathways toward the emergence of novel device design features including the different ways of applying uniform strain, are discussed.Comment: arXiv admin note: text overlap with arXiv:1509.00912, arXiv:1009.4548 by other author

Extrinsic Magnetotransport Phenomena in Ferromagnetic Oxides

This review is focused on extrinsic magnetotransport effects in ferromagnetic oxides. It consists of two parts; the second part is devoted to an overview of experimental data and theoretical models for extrinsic magnetotransport phenomena. Here a critical discussion of domain-wall scattering is given. Results on surfacial and interfacial magnetism in oxides are presented. Spin-polarized tunnelling in ferromagnetic junctions is reviewed and grain-boundary magnetoresistance is interpreted within a model of spin-polarized tunnelling through natural oxide barriers. The situation in ferromagnetic oxides is compared with data and models for conventional ferromagnets. The first part of the review summarizes basic material properties, especially data on the spin-polarization and evidence for half-metallicity. Furthermore, intrinsic conduction mechanisms are discussed. An outlook on the further development of oxide spin-electronics concludes this review.Comment: 133 pages, 47 figures, submitted to Rep. Prog. Phy

Study of Structural, Magnetic and Magnetocaloric Properties of (1-x) La0.7Ca0.3MnO3-xMO (M = Ni, Cu, Co) Nanocomposites.

Manganites have shown potential application as magnetic refrigerants due to the exhibition of near room temperature magnetocaloric effect. High relative cooling power (RCP) values and the easy tunability of magnetic phase transition temperature (Tc), magnetic entropy change (?Sm), and RCP opens up a lot of possibilities for exploring better magnetocaloric materials. Reported literature shows doped manganites and composites with significant improvement in magnetocaloric properties. In this work, we have synthesized (1-x) La0.7Ca0.3MnO3-xMO (x = 2.5%, 5%; M = Ni, Cu, Co), magnetite-metal oxide nanocomposites using a simple autocombustion method. The structural and magnetic measurements have been made to explore the purity and the magnetocaloric properties of the sample. The x-ray diffraction data (XRD) of all the samples show the presence of a pure LCMO phase. The presence of metal oxides is further confirmed by energy-dispersive spectroscopy (EDS). The field Cooled magnetization curve shows that the material undergoes second-order PM-FM transition as we decrease the temperature. The obtained phase transition temperature (Tc) drops with the increasing content of metal oxides. The highest drop of Tc is observed from 258 K in pure LCMO to 166.6 K in LCMO-5%CoO. Isothermal magnetization curves for the composites also show PM-FM phase transition with the change in nature of the curve. The maximum magnetic entropy change (?Smax) is observed around Tc for all the samples, and it increases with the increase in the applied field. The largest drop in?Smax is observed from 8.77 JKg-1K-1 in pure LCMO to 3.24 JKg-1K-1 in LCMO-5%NiO. The most important parameter in quantifying the magnetocaloric behavior of the sample, RCP, is calculated, and it is found to increase linearly with the externally applied field. The RCP values increase with the increase in metal oxide content despite the decrease in?Smax. The highest value for RCP obtained is 266.89 JKg-1 in LCMO-5%CuO, which is a 23.4% gain from 213.13 JKg-1 for pure LCMO. The increase in RCP values with the increase in metal oxide content signifies that we were able to tune and improve the magnetocaloric behavior of LCMO by composite formation