Title Crystal structure and magnetic properties of bi(1-x)ca(x)fe(1-y)mn(y)o3 multiferroics near the polar - anti(non)polar phase boundry /
Translation of Title Bi(1-x)Ca(x)Fe(1-y)Mn(y)O3 multiferoinių medžiagų magnetinės savybės ir kristalinė struktūra prie polinės-anti(ne)polinės fazių ribos.
Authors Skaržinskas, Mantas
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Pages 65
Keywords [eng] feroelektriniai feromagnetai, multiferoikai, polinė, nepolinė, antipolinė, anti(ne)polinė, fazė, kristalo struktūra, magnetinės savybės, skenuojantis elektroninis mikroskopas, vibruojančio mėginio magnetometrija, rentgeno spindulių difrakcija, magnetoelektrinis efektas, perovskitai, antiferomagnetizmas, bismuto feritas, poliarizacija, magnetizacija. ferroelectric ferromagnets, multiferroics, polar, nonpolar, antipolar, anti(non)polar, phase, crystal structure, magnetic properties, scanning electron microscope, vibrating sample magnetometry, X-ray diffraction, magnetoelectric effect, perovskites, antiferromagnetism, bismuth ferrite, polarization, magnetization.
Abstract [eng] The development of multiferroic materials with magnetoelectric properties remains a focus of significant research. Although progress has been made in this field, certain areas still require deeper understanding. Researchers have yet to find an effective method to combine spontaneous magnetization and polarization in a classic multiferroic compound, such as BiFeO3, at room temperature. The impact of chemical substitution on the properties of the material is critical, as it strongly influences multiferroic characteristics. This project aims to explore an alternative method to achieve substantial switchable magnetization in a ferroelectric compound. This method involves the partial substitution of Fe^{3+} ions with a manganese mixture (Mn^{3+}/Mn^{4+}), where the oxidation state ensures ferromagnetic exchange coupling Mn^{3+}: t_{2g}^3 e_g^1 &#8210; O &#8210; Mn^{4+}: t_{2g}^3 e_g^0. Such a method can be implemented in Bi(1-x)AE(x)Fe(1-y)Mn(y)O3 system, where the charge imbalance arises from substituting Bi^{3+} with AE^{2+} and is compensated by Mn^{4+} (coexisting with Mn^{3+} when y > x). In this thesis, X-ray diffraction, scanning electron microscopy, and vibrating sample magnetometry measurements were conducted to determine the crystalline structures and magnetic properties of samples in the Bi(1-x)Ca(x)Fe(1-y)Mn(y)O3 perovskite system. X-ray diffraction (XRD) measurements and Rietveld refinement analysis revealed the crystallographic structure of the samples and identified a structural transition from polar to anti(non)polar phase. This transition becomes noticeable when x = 0.10 (antipolar), x = 0.15 (nonpolar), and begins to appear in the Mn concentration range of 0.40 < y < 0.45. Compounds with y <= 0.40 demonstrated consistent alignment with a primitive pseudocubic perovskite crystalline lattice, belonging to the R3c space group, confirming the ferroelectric nature of these compounds. Analysis of scanning electron microscopy images revealed different grain boundaries, indicating changes in grain sizes and the existence of different crystalline domains within the sample. Furthermore, the study confirmed the phase purity of the sample by comparing secondary electron microscopy images and backscattered electron microscopy images. In this case, no composition-dependent contrast fluctuations were observed, indicating the absence of secondary phases in the sample. Vibrating sample magnetometry measurements show that all samples exhibit linear dependence on the magnetic field, suggesting a paramagnetic or collinear (G-type) antiferromagnetic state at room temperature. Samples with y = 0.35, 0.40 showed an unusual temperature dependence, transitioning from a collinear G-type antiferromagnetic state to a weakly ferromagnetic state as the temperature decreased. Additionally, the magnetization of samples at T = 2 K with compositions [0,10, 0,40], [0,10, 0,45], [0,15, 0,45] significantly exceeds the typical values obtained for weakly ferromagnetic bismuth ferrites at the polar/anti(non)polar phase boundary.
Dissertation Institution Vilniaus universitetas.
Type Master thesis
Language English
Publication date 2024