Abstract
Electric noise spectroscopy is a non-destructive and a very sensitive method for studying the dynamic behaviors of the charge carriers and the kinetic processes in several condensed matter systems, with no limitation on operating temperatures. This technique has been extensively used to investigate several perovskite compounds, manganese oxides (La1−xSrxMnO3, La0.7Ba0.3MnO3, and Pr0.7Ca0.3MnO3), and a double perovskite (Sr2FeMoO6), whose properties have recently attracted great attention. In this work are reported the results from a detailed electrical transport and noise characterizations for each of the above cited materials, and they are interpreted in terms of specific physical models, evidencing peculiar properties, such as quantum interference effects and charge density waves.
Highlights
Perovskite magnetic materials have been studied for almost 50 years. These systems offer a degree of chemical flexibility which allows the relation between the oxides structure, and electronic and magnetic properties that can be controlled in various ways, such as: Doping [61,62,63], magnetic field [64,65,66], electric field [67,68], temperature [69,70,71], pressure, and photoexcitation [72,73,74,75]
Sr2 FeMoO6 (SFMO) polycrystalline samples fabricated by pulsed laser deposition (PLD) technique (Section 4.1); La1−x Srx MnO3 (LSMO) ultrathin films deposited by molecular beam epitaxy (MBE) technique (Section 4.2); La0.7 Ba0.3 MnO3 (LBMO) thin films grown by using PLD on STO and MgO substrates (Section 4.3); Pr0.7 Ca0.3 MnO3 (PCMO) epitaxial samples realized under tensile strain in a PLD chamber (Section 4.4); and manganese oxides of the general composition R1–x Ax MnO3, prepared with different fabrication methods, which evidence the occurrence of quantum interference effects (QIEs) and WL phenomena (Section 4.5)
The ordered double perovskite SFMO is characterized by a pronounced negative magnetoresistance at low magnetic fields and high temperatures, induced by a spin polarization of the charge carriers [90]
Summary
The so-called magnetoresistance (MR) effect and the interplay between spin [5], orbital [6], charge, and structural degrees of freedom [7], have been investigated in polycrystals, single crystals, and thin films All these phenomena have been the subject of a great deal of research, in view of possible applications in spin electronics and magnetism. While a standard noise behavior is observed with STO substrates, an anomalous behavior is found in the MgO case Such anomalous temperature dependence of the measured noise, in the ferromagnetic metallic region, for LBMO-MgO samples is interpreted by considering an enhanced spin ordering with increasing bias currents.
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