Role of double exchange interaction on the magnetic and electrical properties of Pr0.8Sr0.2MnO3 ferromagnetic insulating manganite
TL;DR: In this article, the ferromagnetic state of a manganite with Pr0.8Sr0.2MnO3 was analyzed and the temperature variation of ac susceptibility was seen to show two transitions with a high temperature transition occurring at 158K and a low temperature cusp (Tf) around 90K.
Abstract: In this work the ferromagnetic state in a ferromagnetic insulating manganite viz. Pr0.8Sr0.2MnO3 was analyzed. The temperature variation of ac susceptibility is seen to show two transitions with a high temperature transition occurring at 158K and a low temperature cusp (Tf) around 90K. The high temperature transition (TC) was found to be independent of frequency while the low temperature transition shifts with frequency indicating a frustrated magnetic state. The relaxation time observed from the critical slowing down spin analysis indicates that this state is that of a cluster glass. Temperature variation of resistivity shows an insulating behavior with two distinct humps corresponding to TC and Tf. Temperature variation of thermopower exhibits a peak at TC and decreases below TC which is attributed to the sudden release of holes from traps, similar to a ferromagnetic metallic manganite. Magnetoresistance is seen to show a change in curvature upon cooling the sample across TC which in conjunction with th...
Citations
More filters
TL;DR: In this article, a strong correlation between the phase formations, structural, magnetic and transport properties as a function of Zr concentration is revealed, which is supported by FTIR wherein, the stretching bond vibrations produce distortion in the Mn-O-Mn symmetry.
Abstract: In the present work, La1−xZrxMnO3 (where x=0.05, 0.10, 0.15 and 0.20) powder samples are synthesized using solid-state reaction and investigated for structural, electrical and magnetic properties using X-ray diffraction, neutron diffraction, FT-IR, resistivity measurement system and SQUID. Structural investigations revealed that all the samples have rhombohedral structure with R 3 ¯ C space group. Moreover, it was observed that the MnO6 octahedra gets rotated due to internal stress after replacement of ‘La’ with ‘Zr’ and results into the bending of Mn–O–Mn bond angle from standard 180°. This is supported by FTIR wherein, the stretching bond vibrations produce distortion in the Mn-O-Mn symmetry. Evolution in the granular morphology from the irregular shape to the interconnected hexagon shape is found with increase in ‘Zr’ concentration. XPS studies revealed ‘Mn’ having mixed valence state of Mn3+ and Mn4+, indicating hole-doping behavior. Decrease in resistivity and increase in metal-insulator transition temperature is observed with increase in ‘Zr’ concentration upto 15%. Furthermore, the magnetic saturation is found to increase upto 15% Zr concentration, beyond which it decreases, significantly. A strong correlation between the phase formations, structural, magnetic and transport properties as a function of ‘Zr’ concentration is revealed.
25 citations
TL;DR: In this paper, a core-shell silica (SiO2)-coated Fe3O4 nanoparticles of shell thickness between 2 and 52nm have been synthesized and characterized.
Abstract: Core-shell silica (SiO2)-coated Fe3O4 nanoparticles of shell thickness between 2 and 52nm have been synthesized and characterized. The saturation magnetization scales with SiO2 wt % and these samples exhibit negligible hysteresis at room temperature, as compared to the bulk Fe3O4. The peak in the temperature-dependent ac susceptibility Tm shifts toward higher temperature with increasing frequency. Data of pristine to 40wt% SiO2-coated samples fit to critical slowing-down behavior model yielding relaxation time of ∼10−10s. For particles of higher shell thickness, smaller relaxation time of ∼10−13s is obtained. Temperature-dependent electron spin resonance measurements suggest overall weakening of magnetic interactions in Fe3O4 nanoparticles of thicker SiO2 shell. Variation of shell thickness in these core-shell nanoparticles could lead to diverse ground states ranging from interacting to noninteracting systems.
16 citations
TL;DR: In this article, the authors investigated the magnetic states of under-doped ferromagnetic-insulating manganite Nd 0.8 Sr 0.2 MnO 3 through temperature-dependent linear and non-linear complex ac magnetic susceptibility measurements.
Abstract: We have thoroughly investigated the entire magnetic states of under-doped ferromagnetic-insulating manganite Nd 0.8 Sr 0.2 MnO 3 through temperature-dependent linear and non-linear complex ac magnetic susceptibility measurements. This ferromagnetic-insulating manganite is found to have frequency-independent ferromagnetic to paramagnetic transition temperature at around 140 K. At around 90 K (≈ T ƒ ) the sample shows a second frequency-dependent re-entrant magnetic transition as explored through complex ac susceptibility measurements. Non-linear ac susceptibility measurements (higher harmonics of ac susceptibility) have also been performed (with and without the superposition of a dc magnetic field) to further investigate the origin of this frequency dependence (dynamic behavior at this re-entrant magnetic transition). Divergence of 3rd harmonic of ac susceptibility in the limit of zero exciting field indicates a spin-glass-like freezing phenomena. However, large value of spin-relaxation time ( τ 0 =10 −8 s) and small value of coercivity (∼22 Oe) obtained at low temperature (below T ƒ ) from critical slowing down model and dc magnetic measurements, respectively, are in contrast with what generally observed in a canonical spin glass ( τ 0 =10 −12 –10 −14 s and very large value of coercivity below freezing temperature). We have attributed our observation to the formation of finite size ferromagnetic clusters which are formed as consequence of intrinsic phase separation and undergo cluster glass-like freezing below certain temperature in this under-doped manganite. The results are supported by the electronic- and magneto-transport data.
15 citations
TL;DR: In this paper, the effect of electron beam (EB) irradiation on the structural, electrical transport and thermal properties of Pr0.8Sr0.2MnO3 manganites has been investigated.
Abstract: In this communication, the effect of electron beam (EB) irradiation on the structural, electrical transport and thermal properties of Pr0.8Sr0.2MnO3 manganites has been investigated. Rietveld refinement of XRD data reveals that all samples are single phased with orthorhombic distorted structure (Pbnm). It is observed that the orthorhombic deformation increases with EB dosage. The Mn–O–Mn bond angle is found to increase with increase in EB dosage, presumably due to strain induced by these irradiations. Analysis on the measured electrical resistivity data indicates that the small polaron hopping model is operative in the high temperature region for pristine as well as EB irradiated samples. The electrical resistivity in the entire temperature region has been successfully fitted with the phenomenological percolation model which is based on phase segregation of ferromagnetic metallic clusters and paramagnetic insulating regions. The Seebeck coefficient (S) of the pristine as well as the irradiated samples exhibit positive values, indicating that holes is the dominant charge carriers. The analysis of Seebeck coefficient data confirms that the small polaron hopping mechanism governs the thermoelectric transport in the high temperature region. In addition, Seebeck coefficient data also is well fitted with the phenomenological percolation model. The behavior in thermal conductivity at the transition is ascribed to the local anharmonic distortions associated with small polarons. Specific heat measurement indicates that electron beam irradiation enhances the magnetic inhomogeneity of the system.
13 citations
TL;DR: The present setup can be used as a multipurpose uniaxial pressure device for the measurement of Hall effect and thermoelectric power with a small modification in the pressure cell.
Abstract: A simple design of the uniaxial pressure device for the measurement of ac-susceptibility at low temperatures using closed cycle refrigerator system is presented for the first time. This device consists of disc micrometer, spring holder attachment, uniaxial pressure cell, and the ac-susceptibility coil wound on stycast bobbin. It can work under pressure till 0.5GPa and at the temperature range of 30–300K. The performance of the system at ambient pressure is tested and calibrated with standard paramagnetic salts [Gd2O3, Er2O3, and Fe(NH4SO4)26H2O], Fe3O4, Gd metal, Dy metal, superconductor (YBa2Cu3O7), manganite (La1.85Ba0.15MnO3), and spin glass material (Pr0.8Sr0.2MnO3). The performance of the uniaxial pressure device is demonstrated by investigating the uniaxial pressure dependence of La1.85Ba0.15MnO3 single crystal with P‖c axis. The Curie temperature (Tc) decreases as a function of pressure with P‖c axis (dTc∕dP‖caxis=−11.65K∕GPa) up to 46MPa. The design is simple, is user friendly, and does not requir...
7 citations
References
More filters
Book•
01 Jun 1972
TL;DR: In this paper, the authors present materials at the practical rather than theoretical level, allowing for a physical, quantitative, measurement-based understanding of magnetism among readers, be they professional engineers or graduate-level students.
Abstract: Introduction to Magnetic Materials, 2nd Edition covers the basics of magnetic quantities, magnetic devices, and materials used in practice. While retaining much of the original, this revision now covers SQUID and alternating gradient magnetometers, magnetic force microscope, Kerr effect, amorphous alloys, rare-earth magnets, SI Units alongside cgs units, and other up-to-date topics. In addition, the authors have added an entirely new chapter on information materials. The text presents materials at the practical rather than theoretical level, allowing for a physical, quantitative, measurement-based understanding of magnetism among readers, be they professional engineers or graduate-level students.
6,573 citations
TL;DR: In this paper, a large variety of experiments reviewed in detail here contain results compatible with the theoretical predictions, including phase diagrams of manganite models, the stabilization of the charge/orbital/spin ordered half-doped correlated electronics (CE)-states, the importance of the naively small Heisenberg coupling among localized spins, the setup of accurate mean-field approximations, and the existence of a new temperature scale T∗ where clusters start forming above the Curie temperature, the presence of stripes in the system, and many others.
Abstract: The study of the manganese oxides, widely known as manganites, that exhibit the “colossal” magnetoresistance effect is among the main areas of research within the area of strongly correlated electrons. After considerable theoretical effort in recent years, mainly guided by computational and mean-field studies of realistic models, considerable progress has been achieved in understanding the curious properties of these compounds. These recent studies suggest that the ground states of manganite models tend to be intrinsically inhomogeneous due to the presence of strong tendencies toward phase separation, typically involving ferromagnetic metallic and antiferromagnetic charge and orbital ordered insulating domains. Calculations of the resistivity versus temperature using mixed states lead to a good agreement with experiments. The mixed-phase tendencies have two origins: (i) electronic phase separation between phases with different densities that lead to nanometer scale coexisting clusters, and (ii) disorder-induced phase separation with percolative characteristics between equal-density phases, driven by disorder near first-order metal–insulator transitions. The coexisting clusters in the latter can be as large as a micrometer in size. It is argued that a large variety of experiments reviewed in detail here contain results compatible with the theoretical predictions. The main phenomenology of mixed-phase states appears to be independent of the fine details of the model employed, since the microscopic origin of the competing phases does not influence the results at the phenomenological level. However, it is quite important to clarify the electronic properties of the various manganite phases based on microscopic Hamiltonians, including strong electron–phonon Jahn–Teller and/or Coulomb interactions. Thus, several issues are discussed here from the microscopic viewpoint as well, including the phase diagrams of manganite models, the stabilization of the charge/orbital/spin ordered half-doped correlated electronics (CE)-states, the importance of the naively small Heisenberg coupling among localized spins, the setup of accurate mean-field approximations, the existence of a new temperature scale T∗ where clusters start forming above the Curie temperature, the presence of stripes in the system, and many others. However, much work remains to be carried out, and a list of open questions is included here. It is also argued that the mixed-phase phenomenology of manganites may appear in a large variety of compounds as well, including ruthenates, diluted magnetic semiconductors, and others. It is concluded that manganites reveal such a wide variety of interesting physical phenomena that their detailed study is quite important for progress in the field of correlated electrons.
2,927 citations
TL;DR: An overview is given here on this "orbital physics," which will be a key concept for the science and technology of correlated electrons.
Abstract: An electron in a solid, that is, bound to or nearly localized on the specific atomic site, has three attributes: charge, spin, and orbital. The orbital represents the shape of the electron cloud in solid. In transition-metal oxides with anisotropic-shaped d-orbital electrons, the Coulomb interaction between the electrons (strong electron correlation effect) is of importance for understanding their metal-insulator transitions and properties such as high-temperature superconductivity and colossal magnetoresistance. The orbital degree of freedom occasionally plays an important role in these phenomena, and its correlation and/or order-disorder transition causes a variety of phenomena through strong coupling with charge, spin, and lattice dynamics. An overview is given here on this "orbital physics," which will be a key concept for the science and technology of correlated electrons.
1,916 citations
TL;DR: In this article, the authors compared the magnetic phase diagrams of four compounds and showed that low $ ǫ-A$ values are required to obtain CMR properties on the rich side, i.e., when a competition between charge order and cluster glass phases occurs.
Abstract: The magnetic phase diagrams of four ${L}_{1\ensuremath{-}x}{A}_{x}{\mathrm{MnO}}_{3}$ series $(L=\mathrm{P}\mathrm{r},\mathrm{S}\mathrm{m};$ $A=\mathrm{C}\mathrm{a},\mathrm{S}\mathrm{r})$ have been established combining neutron diffraction, electron microscopy, and magnetotransport measurements in order to understand and optimize the colossal magnetoresistance (CMR) properties of these compounds. A complementary study of the ${\mathrm{La}}_{1\ensuremath{-}x}{\mathrm{Ca}}_{x}{\mathrm{MnO}}_{3}$ phase diagram $(xg~0.8)$ is also performed. The comparison of these diagrams demonstrates that low $〈{r}_{A}〉$ values are required to obtain CMR properties on the ${\mathrm{Mn}}^{4+}$ rich side, i.e., when a competition between charge order and cluster glass phases occurs ${(L}_{1\ensuremath{-}x}{\mathrm{Ca}}_{x}{\mathrm{MnO}}_{3};$ $L=\mathrm{P}\mathrm{r},\mathrm{S}\mathrm{m}).$ As a consequence of the low $〈{r}_{A}〉$ values on the rich ${\mathrm{Mn}}^{3+}$ side $(xl0.5$ in ${L}_{1\ensuremath{-}x}{\mathrm{Ca}}_{x}{\mathrm{MnO}}_{3}),$ the ferromagnetic metallic (FMM) state is never reached, whereas for the same x values, systems with larger $〈{r}_{A}〉$ ${(L}_{1\ensuremath{-}x}{\mathrm{Sr}}_{x}{\mathrm{MnO}}_{3};$ $L=\mathrm{P}\mathrm{r},\mathrm{S}\mathrm{m})$ exhibit CMR properties related to the FMM state. A particular attention is paid to the $x\ensuremath{\sim}0.5$ compositions of these ${L}_{1\ensuremath{-}x}{\mathrm{Sr}}_{x}{\mathrm{MnO}}_{3}$ series for which the Curie and N\'eel temperatures are ${T}_{N}l{T}_{C}$ and ${T}_{C}l{T}_{N}$ for Pr and Sm, respectively. The importance of the chemical factors on the charge ordering (studied vs temperature by electron diffraction) and on the magnetic structures (from neutron diffraction) is also emphasized.
460 citations
TL;DR: In this article, a modification of Mott's original model was proposed by taking into account that the hopping barrier depends on the misorientation between the spins of electrons at an initial and a final state in an elementary hopping process.
Abstract: The low carrier mobility of the magnetic perovskite ${\mathrm{Nd}}_{0.52}{\mathrm{Sr}}_{0.48}{\mathrm{MnO}}_{3}$ implies that the dominant conductivity mechanism is related to Mott hopping. We propose a modification of Mott's original model by taking into account that the hopping barrier depends on the misorientation between the spins of electrons at an initial and a final state in an elementary hopping process. Using this model we deduce a negative-magnetoresistivity scaling proportional to the Brillouin function $B$ in the ferromagnetic state and to ${B}^{2}$ in the paramagnetic state. Both predictions are in full agreement with the magnetoresistivity measured in pulsed magnetic fields up to 50 T.
133 citations