arXiv subjects

M. Manikandan

Publications and source records attributed to M. Manikandan.

9 recordsLinked to original sources

arXiv2026

High-frequency magnetotransport in LaMnO3 samples synthesized by microwave irradiation versus conventional heating

Magnetoresistance of hole-doped LaMnO3 at frequencies above a few MHz has been seldom reported compared to numerous studies on magnetoresistance measured at direct current. Here, we contrast the high-frequency magnetoresistance in the frequency range f = 0.9-3 GHz in polycrystalline LaMnO3 (LMO) synthesized by microwave irradiation of oxide precursors in a microwave furnace (MW-LMO) and by conventional heating (CH-LMO) in an electrical furnace. The structure at room temperature changed from orthorhombic in CH-LMO to rhombohedral in MW-LMO. A combination of magnetization and resistivity studies suggest that the CH-LMO sample is a canted antiferromagnetic insulator below 140 K but the MW-LMO is a ferromagnetic metal with T_C = 240 K. While the high-frequency resistance of the CH-LMO sample at 300 K decreases gradually with increasing strength of the applied dc magnetic field for all f, a peak appears at H = H_r larger than 0 gauss when f equal or greater than 1.4 GHz in the MW-LMO sample and H_r increases linearly with f. We attribute the observed features in the high-frequency magnetoresistance of MW-LMO to current-driven resonant excitation of spins in the paramagnetic state. Its absence in the CH-LMO sample highlights the need for an optimum hole density to observe this effect.

physics.app-ph↗

arXiv2026

Magnetovolume effect in SrRu1-xCoxO3 (x = 0.0, 0.05)

Polycrystalline SrRu1-xCoxO3 (x = 0.0, 0.05) and CaRuO3 were rapidly synthesized (< 1 hour) by microwave irradiation of oxide powders, and their magnetic, magnetoresistance, thermal expansion, and magnetostriction properties were investigated. The microwave-synthesised SrRuO3 exhibits a ferromagnetic transition at TC = 160 K, metallic-type resistivity, and negative magnetoresistance, with magnitudes comparable to those of a sample synthesized by conventional heating over 24 hours. Upon lowering the temperature from 300 K, the linear thermal expansion shows a transition from the usual contraction in the paramagnetic state to spontaneous expansion in the ferromagnetic state (invar-like effect). The application of an external magnetic field at a fixed temperature results in isotropic expansion of the length, implying a positive magnetovolume effect. The volume magnetostriction is 40 ppm at 10 K in a magnetic field of 50 kOe, and it reaches a maximum value of 60 ppm close to TC. The spontaneous thermal expansion is diminished in SrRu0.95Co0.05O3. While the magnetostriction is anisotropic at 10 K, the isotropic behaviour is recovered above 80 K, and the maximum value of the positive magnetovolume is comparable to that of the parent compound. Our results suggest that the magnetovolume effect in SrRu1-xCoxO3 is related to competition between robust tilting/rotation of RuO6 octahedra and spin-orbit interaction of the doped Co2+ ions

cond-mat.str-el↗

arXiv2026

Evolution of anisotropic magnetostriction in LaMn1-xCoxO3 (x= 0.1-0.9)

Polycrystalline samples of LaMn1-xCoxO3 series over a wide compositional range (x = 0.1 - 0.9) were synthesized by microwave irradiation of oxide precursors and their magnetic and magnetostrictive properties were investigated. Magnetostrictions parallel (l_par) and perpendicular (l_per) to the applied magnetic field were measured to estimate anisotropic(l_anis) and volume magnetostrictions(l_vol). In all the compositions, l-par (l_per) is negative (positive) and (l_anis) >> (l_vol), suggesting dominance of anisotropic lattice distortion under a magnetic field. The value of l_anis at 10 K for H = 50 kOe initially increases with x from 178 ppm for x = 0.1 to a maximum of 1221 ppm at x = 0.5 before decreasing for higher x. The composition dependence of magnetostriction is asymmetric about x = 0.5, the decrease for x > 0.5 is more steeper than for x < 0.5 whereas saturation magnetization decreases monotonically with increasing x except for an abrupt change at x = 0.6. The largest anisotropic magnetostriction observed for x = 0.5 is attributed to the presence of high-spin Co2+ ions with a non-zero orbital moment in the maximum fraction whereas Mn3+/4+ or Co3+ ions play minor roles. The composition dependence of magnetostriction is suggested to arise from changes in the structure, valence states of Mn and Co ions and magnetic interactions among them.

cond-mat.str-el↗

arXiv2025

Enhanced magnetic, electrical, and magnetostrictive properties of La-doped SrCoO3 synthesized by microwave heating

We report microwave-assisted synthesis and physical properties of La-doped SrCoO3-{\delta}. The Sr0.8La0.2CoO3-{\delta} synthesized via microwave heating (MWH) exhibits superior physical properties compared to a nominally identical composition obtained by conventional heating (CH) in an electrical furnace. The MWH sample exhibits an enhanced ferromagnetic Curie temperature (158 K in CH and 176 K in MWH samples) and higher saturation magnetization but smaller coercive field and magnetoresistance at 10 K compared to the CH sample. While the dc resistivity increases substantially below 120 K in the CH sample, it is metallic from 350 to 10 K in the MWH sample. Further, the longitudinal magnetostriction of the MWH sample ({\lambda}par = 247 ppm for H = 50 kOe) at 10 K is also higher than that of the CH sample ({\lambda}par = 128 ppm). The observed enhanced properties of the MWH sample can not be attributed to grain size and grain boundaries but are likely to arise from lesser oxygen defects and partial oxidation of Co3+ into Co4+, however, the exact mechanism is not fully understood at present.

cond-mat.mtrl-sci↗

arXiv2023

Giant magnetostriction in La2CoMnO6 synthesized by microwave irradiation

Polycrystalline insulating ferromagnetic double perovskite La2CoMnO6 possessing monoclinic structure and a high ferromagnetic Curie temperature (TC = 222 K) was rapidly synthesized ( 30 min) by irradiating stoichiometric mixture of oxides with the microwave. The sample exhibits negative magnetostriction, i.e., contraction of length along the magnetic field direction in the ferromagnetic state. At 10 K, the parallel magnetostriction does not show saturation up to a magnetic field of 50 kOe where it reaches 610 ppm which is one of the highest values of magnetostriction found so far among perovskite oxides with 3d ions. The magnitude of magnetostriction decreases monotonically as the temperature increases and becomes negligible above TC. The giant magnetostriction in this double perovskite is suggested to originate from large spin-orbit coupling associated with Co2+ (d7) cation. The obtained magnetostriction value is comparable to 630 ppm in an identical composition obtained through solid-state reaction over several days in a conventional furnace which indicates the advantages of microwave-assisted synthesis in saving reaction time and electric power without deteriorating physical properties.

cond-mat.mtrl-sci↗

arXiv2022

Magnetostriction in microwave synthesized La0.5Ba0.5CoO3

A single-phase polycrystalline La0.5Ba0.5CoO3-d sample was synthesized by microwave irradiation within 20 minutes of processing time and its structural, magnetic, electrical, and magnetostrictive properties were investigated. While the temperature dependence of field-cooled magnetization (M) in a field of H = 0.5 kOe indicates the onset of ferromagnetic transition at TC = 177 K, irreversibility between the zero field-cooled and field cooled M(T) persists even at H = 3 kOe. M(H) at 10 K does not saturate at the maximum available field and has a much smaller value (0.87 {\mu}B/Co in a field of 50 kOe) than 1.9 {\mu}B/Co expected for spin-only contribution from intermediate Co3+ and Co4+ spins. The resistivity shows insulating behavior down to 10 K and only a small magnetoresistance (~ 2% for H = 70 kOe) occurs around TC. All these results suggest a magnetically heterogeneous ground state with weakly interacting ferromagnetic clusters coexisting with a non-ferromagnetic phase. The length of the sample expands in the direction of the applied magnetic field (positive magnetostriction) and does not show saturation even at 50 kOe. The magnetostriction has a maximum value (= 252 ppm) at 10 K and it decreases with increasing temperature. The smaller value of magnetostriction compared to the available data on La0.5Sr0.5CoO3 suggests that non-ferromagnetic matrix is most likely antiferromagnetic and it restrains the field-induced expansion of ferromagnetic clusters in the microwave synthesized La0.5Ba0.5CoO3-d sample.

cond-mat.mtrl-sci↗

arXiv2022

Anomalous Nernst effect in La0.5Ca0.5Coo3

We report the occurrence of the anomalous Nernst effect (ANE) in polycrystalline perovskite La0.5Ca0.5CoO3. The sample is ferromagnetic below TC = 147 K and resistivity shows non-metallic behavior above and below the TC with only a small negative magnetoresistance (~2%) around TC. Field dependence of magnetization at 10 K shows large hysteresis with a coercive field of 6 kOe but a small magnetization ~ 0.64 Bohr magneton/Co even in a field of 50 kOe, which indicates the presence of magnetically heterogeneous ground state consisting of ferromagnetic and non-ferromagnetic phases. The field dependence of the Nernst thermopower (Sxy) at low temperatures shows complete saturation but the magnetization does not. This indicates that the ANE in La0.5Ca0.5CoO3 depends only on the transport properties of the ferromagnetic phase, while it is not affected by the non-ferromagnetic phase. Due to the higher value of remnant Sxy, the magnetized polycrystalline sample exhibits ANE in absence of an external magnetic field.

cond-mat.mtrl-sci↗

arXiv2021

Anomalous Nernst thermopower and giant magnetostriction in microwave synthesized La0.5Sr0.5CoO3

Ferromagnetic metallic oxides have potential applications in spincaloric devices which utilize the spin property of charge carriers for interconversion of heat and electricity through the spin Seebeck or the anomalous Nernst effect or both. In this work, we synthesized polycrystalline La0.5S0.5CoO3 by microwave irradiation method and studied its transverse thermoelectric voltage (Nernst thermopower) and change in the linear dimension of the sample (Joule magnetostriction) in response to external magnetic fields. In addition, magnetization, temperature dependences of electrical resistivity, and longitudinal Seebeck coefficient (Sxx) in absence of an external magnetic field were also measured. The sample is ferromagnetic with a Curie temperature of TC = 247 K and shows a metal-like resistivity above and below TC with a negative sign of Sxx suggesting charge transport due to electrons. Magnetic field dependence of the Nernst thermopower (Sxy) at a fixed temperature shows a rapid increase at low fields and a tendency to saturate at high fields as like the magnetization. Anomalous contribution to Sxy was extracted from total Sxy measured and it exhibits a maximum value of ~ 0.21 microV/K at 180 K for H = 50 kOe, which is comparable to the value found in a single crystal for a lower Sr content. The Joule magnetostriction is positive, i.e., the length of the sample expands along the direction of the magnetic field and it does not saturate even at 50 kOe. The magnetostriction increases with decreasing temperature below TC and reaches a maximum value of 500 ppm at T = 40 K and below. Coexistence of the anomalous Nernst thermopower and giant magnetostriction in a single compound has potential applications for thermal energy harvesting and low-temperature actuators, respectively.

cond-mat.mtrl-sci↗

arXiv2019

Crossover to negative dielectric constant in perovskite PrMnO3

Negative dielectric constant materials, once an incumbrance for physicists, are now the stockpiles of unique optical and microwave devices that will also avoid complex geometries. We report the observation of temperature dependent negative dielectric constant (NDC) above 503 K in the perovskite PrMnO3, confirmed through impedance spectroscopy, obeying classical Drude theory. The principle behind the associated negative dielectric loss is explained using the Axelrod mechanism.

cond-mat.mtrl-sci↗