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3 (x=0; 0.07)
Published in R D Tomlinson, A E Hill, R D Pilkington, Ternary and Multinary Compounds, 2020
N.N. Loshkareva, Yu.P. Sukhorukov, A.P. Nossov, V.G. Vassiliev, B.V. Slobodin, K.M. Demchuk, N.G. Bebenin, V.V. Ustinov
Lanthanum manganites of perovskite structure attract renewed attention because of «colossal» magnetoresistance (CMR) near the room temperature and perspectives of practical applications. Parent LaMnO3 is antiferromagnetic insulator. Substitution of La by divalent ions (Ba, Sr, Ca) results in increasing conductivity, appearance of spontaneous magnetization and the CMR near the Curie temperature Tc. Large magnetoresistance in the vicinity of the phase transition point is typical for magnetic semiconductors [1] with strong interaction between localized spins and electrons moving in a wide band. In contrast, in most compounds of perovskite type (non-magnetic or antiferromagnetic) the low mobility charge carriers - polarons - are responsible for conductivity. Apparently, understanding nature of CMR in the La manganites is impossible without knowing mechanism of conductivity both in ferro- and paramagnetic phases. The present work aims to obtain information on conductivity mechanism in La0.67−xYxBa0.33MnO3 (x=0; 0.07) by studying reflection and absorption spectra in middle infrared where the interaction of light with charge carriers is clearly pronounced.
Magnetics and Piezoelectrics
Published in Debasish Sarkar, Nanostructured Ceramics, 2018
Magnetoresistance change, (MR%), refers to the magnitude of electrical resistance change in presence of magnetic field. Usually, the MR effect depends on both the strength and direction of magnetic field with respect to current. In the perspective of efficiency level, four distinct magnetoresistances can be classified as ordinary magnetoresistance, anisotropic magnetoresistance (AMR), giant magnetoresistance (GMR), and colossal magnetoresistance (CMR) [14]. As an example, ordinary magnetoresistance behavior is found in Sn, Cu, Ag, Au, Mg, Cd, Ga, Pt, Pb, etc., AMR in ferro (Fe, NiFe, etc.), and ferrimagnetic (cobalt ferrite, etc.); GMR in zinc ferrite, Fe/Cr multilayer etc., CMR in La1-xMxMnO3+ (M = Ca, Sr; x = 0.33) perovskite structures. In fact, their efficiency level varies with a wide range 2% for AMR, 50% for GMR, and more than 99% for CMR. In fact, these specific features have different modes of utilities, including recording heads, hyperthermia treatment, biosensors, MEMs, magneto transport systems, etc. This can be quantified as: () MR(%)=(RH−RO)RH×100
Magnetic Properties
Published in Yip-Wah Chung, Monica Kapoor, Introduction to Materials Science and Engineering, 2022
In our quest to reduce the size of magnetic domains in disk drives (to increase the areal storage density), we also reduce the magnetic signal. Before 1992, the same inductive coil used for writing bits was employed for reading as well. This method ran into sensitivity problems as we increased the storage density to the 100 Gbits/in2 regime. Today, we use a different sensing technique based on the phenomenon of magnetoresistance (MR) – the change of electrical resistance due to a magnetic field. Depending on how strong the magnetic field effect is on the electrical resistance, we use different names to describe this phenomenon: giant magnetoresistance (GMR) and colossal magnetoresistance (CMR).
Phenomenological modeling of magnetic and magnetocaloric properties in rare earth doped La0.8Ca0.2MnO3
Published in Phase Transitions, 2019
M. Khlifi, Kh Dhahri, J. Dhahri, E. Dhahri, E. K. Hlil
The cooling systems are numerous and are based on different techniques. Nevertheless, the majority use the mechanism of compression and expansion of gases such as Freon. This technique has a dangerous disadvantage such as the release of chlorofluorocarbons gases responsible for the greenhouse effect and the destruction of the ozone layer. For these reasons, it is essential to replace conventional cooling systems with other ecological techniques that consume less energy. The magnetic refrigeration (MR) technology based on magnetocaloric effect (MCE) of some magnetic materials is more energy efficient and more environmentally friendly. Among the magnetocaloric materials, the manganese oxides also called manganites. Manganese perovskite oxides have and very important physical properties such as the colossal magnetoresistance [1–3] and the MCE [4–6] which are applied in the spintronic field for information storage and modest MR. These materials are generally crystallized in a perovskite structure and have a magnetic phase transition from ferromagnetic (FM) to paramagnetic (PM) state at the Curie temperature (TC). The FM behavior is explained by the Weiss molecular field [7], the basis of the mean field theory and by the double exchange interaction between Mn3+ and Mn4+ ions [8].
Correlation between magnetocaloric and electrical properties based on phenomenological models in La0.47Pr0.2Pb0.33MnO3 perovskite
Published in Phase Transitions, 2018
Nesrine Mechi, Bandar Alzahrani, Sobhi Hcini, Mohamed Lamjed Bouazizi, Abdessalem Dhahri
The temperature dependence of electrical resistivity for different magnetic fields (0 ≤ μ0H ≤ 5 T) for La0.47Pr0.2Pb0.33MnO3 sample between 50 and 400 K is depicted in Figure 7. Using the sign of the temperature coefficient of resistivity ρd/dT as a criterion (ρd/dT < 0 for a semiconductor-like system and ρd/dT > 0 for a metallic system), our sample exhibits a metallic-like behavior at low temperature (T < TMS) and a semiconductor-like above TMS, where TMS is the metal–semiconductor temperature transition at the maximum value of the resistivity. Figure 7 also shows that the resistivity is found to decrease with increasing magnetic field which infers the existence of colossal magnetoresistance (CMR) effect. On the other hand, it can be seen from Figure 7 that the TMS shifts slightly to higher temperature side with increasing magnetic field. This may be due to the fact that the applied magnetic field induces delocalization of charge carriers, which in turn might suppress the resistivity and also cause local ordering of the magnetic spins. Due to this ordering, the ferromagnetic metallic (FMM) state may suppress the paramagnetic semiconductor (PMS) regime. In fact, randomly oriented moments of particles can be aligned by an external field. This causes a significant increase in tunnel conductance, thereby reducing resistivity of the granular system [27].
Room temperature magnetoimpedance of La0.67Sr0.33–xPbxMnO3 (x = 0–0.33) manganites
Published in Phase Transitions, 2019
Perovskite Manganites have been a subject of multidisciplinary research since last few years in the areas of solid–state physics, chemistry, materials science, etc. They exhibit a dramatic change in resistivity in presence of an external magnetic field, known as the colossal magnetoresistance (CMR) effect. But at room temperature under a low magnetic field, the CMR materials show a small value of dc magnetoresistance (MR) which restricts the practical applications of these materials. Hence, many recent investigations have been focused on their ac MR and magnetoimpedance (MI).