Manganite La0 Research Articles

Improvement of magnetocaloric properties around room temperature in (1−x) La0.6Ca0.4MnO3/(x) La0.6Sr0.4MnO3 (0 ≤ x ≤ 1) composite system

ABSTRACTIn this research paper, a detailed investigation is conducted on the magnetocaloric effect (MCE) properties of the two phases (1−x) La0.6Ca0.4MnO3/(x) La0.6Sr0.4MnO3 composite system by experiments and numerical calculations. The polycrystalline manganites La0.6Ca0.4MnO3 and La0.6Sr0.4MnO3 are synthesized by the citric-gel method. Rietveld refinements of the X-ray diffraction patterns show that both samples are single phase. The Curie temperature Tc is found to be 255 and 365 K for La0.6Ca0.4MnO3 and La0.6Sr0.4MnO3, respectively. The study of the temperature dependence of the magnetic entropy change of (1−x)La0.6Ca0.4MnO3/(x)La0.6Sr0.4MnO3 composite indicates that the optimum composition stands for x = 0.6. Indeed, it gives comparable contributions of two parent compounds, leading to a practically uniform variation of entropy over a wide temperature range. The theoretical modeling of the MCE using Landau theory reveals an acceptable concordance with experimental data indicating the importance of magnetoelastic coupling and electron interaction in the MCE properties of manganite systems.

Suppression of Spin Glass Behavior in Phase Separated La0.22Pr0.40Ca0.38MnO3 by Nanostructuring

Spin glass behavior of phase-separated (PS) manganite La0.22Pr0.40Ca0.38MnO3 is investigated as a function of crystallite size. Various sizes are obtained by heating the chemically synthesized compound at 700 °C (S7) and 1100 °C (S11) for 12 h. Rietveld refinement confirms the single-phase orthorhombic structure. The HRTEM analysis yield typical crystallite size in the range of ~10–20 nm for S7 and ~300–500 nm for S11, respectively. At larger crystallite size (S11) charge ordering (CO), antiferromagnetic (AFM), and ferromagnetic (FM) transitions are observed sequentially at $T_{\mathrm {CO}} \sim 230$ K, $T_{N} \sim ~175$ K, and $T_{C} \sim 130$ K, respectively. Spin freezing appears at $T K while a weak reentrant magnetic order is seen at further lower temperatures. At nanoscale (S7) CO and AFM transitions do not remain explicit and $T_{C}$ and $T_{P}$ are lowered to ~107 and ~96 K, respectively. In S11, the frequency dispersion of imaginary part spin freezing temperature ( $T_{f} \approx 104$ K) in the Vogel–Fulcher framework yields a relaxation time $\tau \approx 2.5 \times 10 ^{-9}$ s, activation energy $E_{a} \approx 25$ meV and VF parameter $T_{0} \sim 87$ K. These results point to the canonical spin-glass behavior. It is interesting to note that the nanostructured sample S7 did not show any frequency dispersion. This confirms the suppression of the spin-glass behavior due to the nanostructuring, which is attributed to the surface/interface enhanced spin disorder.

Effect of External Factors on Magnetism of Fluctuating Low-Dimensional Electron and Spin Correlations in Frustrated Manganites La1 – ySmyMnO3 + δ (y = 0.85, 1.0)

The effect of external factors on the temperature dependences of the magnetization of frustrated manganites La1 – ySmyMnO3 + δ (δ ~ 0.1, y = 0.85, 1.0) is studied. Two sharp peaks M(T) of different intensities detected in both samples at close temperatures Т1 and Т2 slightly higher than the critical temperature Tc of the coherent superconducting transition corresponds to the Lindhard divergence χL(qnest) of the temperature dependence of the paramagnetic susceptibility of stripelike 1D electron/spin correlations modulated with wave vectors qnest1 = 2kF1 and qnest2 = 2kF2. The formation and evolution of magnetization features with increasing field are explained by the appearance of spatial modulation of electrical and magnetic properties in ab planes in the case of total nesting of electron–hole areas of the Fermi surface. This appears as two fragments of two fluctuating quasi-one-dimensional charge/spin density waves with wave vector q1 || a and q2 || b directions incommensurate with the lattice. It is assumed that the strong dependence of the magnetization of fluctuating 1D charge/spin density wave correlations on external influences is caused by the immediate vicinity of sample properties to the quantum critical point.

Correlation between magnetic and transport properties of rare earth doped perovskite manganites La0.6R0.1Ca0.3MnO3 (R = La, Nd, Sm, Gd, and Dy) synthesized by Pechini process

Here, we report a comparative study of rare earth doped La0.6R0.1Ca0.3MnO3 (R = La, Nd, Sm, Gd, and Dy) samples synthesized by sol-gel Pechini process. All the compounds are single-phased and crystallize in Pbnm space group with orthorhombic symmetry. Temperature dependent magnetization measurements revealed that all our compounds exhibit a paramagnetic (PM)–ferromagnetic (FM) transition with decrease in both ordering temperature TC and the freezing temperature TF with decrease in ionic radii of lanthanide ions. The compounds display metal-semiconductor transition and the temperatures (TMS) obtained from the electrical resistivity measurements are consistently higher than those of the Curie temperatures TC. The transport properties are dominated by the Variable-range hopping (VRH) model above TMS, showing an increase in characteristic VRH temperature with decreasing size of rare-earth ion. The estimated hopping distance (RH) in all the samples is close to nearest neighbor Mn–O–Mn distance (~5 Å) in the ab plane.

Spin current and magnetic measurements in heterostructure SrIrO3/La0.7Sr0.3MnO3

The dc voltage on the film SrIrO3 (SIO) generated under ferromagnetic resonance condition has been studied in the heterostructure based on manganite thin epitaxial films La0.7Sr0.3MnO3 (LSMO). The SIO film is a paramagnetic metal with strong spin-orbit interaction in the temperature range 20-300K. The effect is shown to be caused by two different phenomena: (1) the resonance dc electromotive force related to anisotropic magnetoresistance (AMR) in the manganite film and (2) pure spin current (spin pumping) registered by means of the inverse spin Hall effect in upper layer. We also give the results of the magnetic parameters measuring for the heterostructure SIO/LSMO using ferromagnetic resonance in a wide temperature range.

SYNTHESIS AND CRYSTALLOCHEMICAL PROPERTIES OF Ce-SUBSTITUTED NANOPARTICLES OF MANGANITE (La,Sr)MnO3

Serious of Ce-substituted lanthanum-strontium man-ganites La0.7–xSr0.3CexMnO3 (x = 0–0.2) nanoparticles were synthesized by sol-gel method with further heat treatment of precursors at 800 °C. Crystallographic properties of obtained nanoparticles were investiga-ted by X-ray diffraction method. According to XRD data, it was established that the substitution of lan-thanum ions by cerium in the crystalline structure and formation of single-phased nanoparticles occurs only up to 5 % mol. of Ce regardless of the heating temperature. Linear decreasing the cell volume of nanoparticles in this concentration range of Ce satis-fies the Vegard law and indicates on the formation of a continuous series of solid solutions with the dis-torted perovskite up to 5 % of Ce. At higher concen-trations of Ce there are additional peaks on the XRD patterns, which point on the formation of an addi-tional phase of CeO2. According to TEM studies, it was calculated that the average size of was 30–40 nm. To estimate heating efficiency of synthesized nanoparticles in the alternating magnetic field, mag-netic fluids based on the synthesized nanoparticles and aqueous dextran solution were prepared. It was shown that they effectively heated up to controlled temperatures in an alternating magnetic field, and their heating efficiency was directly proportional to the increase of the concentration of cerium. Accor-ding to the results of the complex studies, it was shown the possibility to synthesize single-phase Ce-substituted nanoparticles of manganite with a pe-rovskite structure. It was established that cerium does not significantly influence on the change of magnetic properties of such nanoparticles and they are promising for further investigations as the in-ducers of magnetic hyperthermia, as well as for the biological tests.

Emerging ferromagnetic phase in self-assembled mixed valence manganite nanowires

Nanoscale magnetism in oxides with the lateral size down to 300 nm is critical for scientific investigation and advanced technological applications such as spintronics, but often complicated to fabricate. Specifically, the emergent magnetic phenomena induced by the size effect attract tremendous attention. In this situation, fabrication of self-assembled nanoarchitectures in complex oxides and strategically modulating their properties are urgently needed. Here, we report the emerging single ferromagnetic phase state in self-assembled nanowires on the thin film surface of mixed valence manganite La0.5Sr0.5MnO3, by using low temperature magnetic force microscopy. The ferromagnetic state can be reversely switched in the presence of an external magnetic field. This work paves the way for manipulating the phase coexistence state without an external field and provides insight into the size limitation for designing next generation electronic and spintronic devices in complex oxide systems.

Versatile and Highly Efficient Controls of Reversible Topotactic Metal–Insulator Transitions through Proton Intercalation

AbstractThe ability to tailor a new crystalline structure and associated functionalities with a variety of stimuli is one of the key issues in material design. Developing synthetic routes to functional materials with partially absorbed nonmetallic elements (i.e., hydrogen and nitrogen) can open up more possibilities for preparing novel families of electronically active oxide compounds. Fast and reversible uptake and release of hydrogen in epitaxial ABO3 manganite films through an adapted low‐frequency inductively coupled plasma technology is introduced. Compared with traditional dopants of metallic cations, the plasma‐assisted hydrogen implantations not only produce reversibly structural transformations from pristine perovskite (PV) phase to a newly found protonation‐driven brownmillerite one but also regulate remarkably different electronic properties driving the material from a ferromagnetic metal to a weakly ferromagnetic insulator for a range of manganite (La1−xSrxMnO3) thin films. Moreover, a reversible perovskite‐brownmillerite‐perovskite transition is achieved at a relatively low temperature (T ≤ 350 °C), enabling multifunctional modulations for integrated electronic systems. The fast, low‐temperature control of structural and electronic properties by the facile hydrogenation/dehydrogenation treatment substantially widens the space for exploring new possibilities of novel properties in proton‐based multifunctional materials.

Magnetic phase transition in La0.8Sr0.2Mn0.9Sb0.1O3 manganite under pressure

The high-pressure evolution of structural and magnetic properties of the single valence Mn3+ manganite La0.8Sr0.2Mn0.9Sb0.1O3 was studied by means of neutron powder diffraction up to 4.5 GPa in the temperature range of 10–300 K. At ambient pressure, a ferromagnetic ground state with the magnetic ordering temperature TC ≈ 175 K is stabilized. Application of high pressure suppresses the initial FM phase and leads to the appearance of a new A-type antiferromagnetic AFM phase with TN ~ 130 K at P = 2.2 GPa. Under compression, both TC and TN almost linearly increases with the pressure coefficient of 1.9(2) and 0.9(3) K/GPa, respectively. It is assumed that the appearance of the A-type AFM state is mediated by the strong anisotropic distortions of MnO6 octahedra, coupled to the egdx2-z2 orbital polarization at high pressures.

Magnetic Interactions on Oxide Ferromagnet/Ferromagnetic Intermetallide Interface

The magnetic properties of heterostructures consisting of two films are studied. The upper layer involves rare-earth intermetallic nanostructured superlattices consisting of exchange-coupled layers (TbCo2/FeCo)n (TCFC), and the lower layer includes either epitaxial manganite La0.7Sr0.3MnO3 (LSMO) with optimum strontium doping or an epitaxial film of an yttrium–iron garnet Y3Fe5O12 (YIG) with a Bi additive. TCFC is a ferromagnet having high Curie temperature and provides controllable induced magnetic anisotropy. Experimental studies showed that the interlayer interaction of the TCFC/LSMO heterostructure is antiferromagnetic. There was an increase in the FMR line width in the structures due to the flow of a spin current through the interface between two films. There was electric voltage in the TCFC/YIG heterostructure induced in the TCFC intermetallide film, due to an inverse spin Hall effect under ferromagnetic resonance conditions.

Magnetocaloric effect and critical behaviour of La0.5Ca0.2Ag0.3MnO3 compound

We present a dc magnetization study of the critical phenomena of a manganite oxide La0.5Ca0.2Ag0.3MnO3 single crystal. Based on the assumption of a continuous (second order) manganite transition for our sample, we have determined the critical temperature Tc = 264 K and the critical exponents β=0.18259±0.004 (β: critical exponent for the temperature dependence of spontaneous magnetization just below TC), γ=0.81967±0.0.029 (γ: critical exponent for the inverse initial susceptibility just above TC) and δ=5.45±0.006 (δ: critical exponent for the Widom scaling relation (T = TC)). From the field dependence of the magnetic entropy ΔSMΔSM∝Hn and the relative cooling power (RCP) RCP∝H∧1+1/δ, it was possible to evaluate the critical exponents of the magnetic phase transitions. Their values are in good agreement with those obtained from the critical exponents using a modified Arrott method.

Unambiguous determining the Curie point in perovskite manganite with second-order phase transition by scaling method

The accurate determination of the Curie temperature (TC) is particularly important in describing the magnetic behavior close to the paramagnetic-ferromagnetic (PM-FM) phase transition. In this paper, we studied the magnetic phase transition and accurately predicted the Curie point of perovskite manganite La0.825Sr0.175MnO3. We find the compound shows a second-order PM-FM transition and has a large magnetic entropy change (MEC) in vicinity of phase transition region. Based on the scaling law and the correlation between magnetic field and MEC, the precise and magnetic-independent Curie temperature was determined to be 281.7 K, obviously lower than 285.4 K decided from the magnetization versus temperature. The reliability of new Curie temperature can be well confirmed by the modified Arrott plot together with the critical exponents. Our results not only open up a new pathway for precise definition of Curie point but also facilitate the efficient exploitation of spontaneous magnetic bubbles in perovskite manganite.

Room temperature Co-doped manganite/graphene sensor operating at high pulsed magnetic fields

The demand to increase the sensitivity to magnetic field in a broad magnetic field ranges has led to the research of novel materials for sensor applications. Therefore, the hybrid system consisting of two different magnetoresistive materials – nanostructured Co-doped manganite La1−xSrx(Mn1−yCoy)zO3 and single- and few-layer graphene – were combined and investigated as potential system for magnetic field sensing. The negative colossal magnetoresistance (CMR) of manganite-cobaltite and positive one of graphene gives the possibility to increase the sensitivity to magnetic field of the hybrid sensor. The performed magnetoresistance (MR) measurements of individual few layer (n = 1–5) graphene structures revealed the highest MR values for three-layer graphene (3LG), whereas additional Co-doping increased the MR values of nanostructured manganite films. The connection of 3LG graphene and Co-doped magnanite film in a voltage divider configuration significantly increased the sensitivity of the hybrid sensor at low and intermediate magnetic fields (1–2 T): 70 mV/VT of hybrid sensor in comparison with 56 mV/VT for 3LG and 12 mV/VT for Co-doped magnanite film, respectively, and broadened the magnetic field operation range (0.1–20) T of the produced sensor prototype.

Electrical Transport Property and Electron Paramagnetic Resonance Research of a Perovskite Manganite

Unique electrical transport properties of double metal-insulator transitions were found in perovskite manganite La0.6Pr0.1Ba0.3MnO3 prepared using the sol-gel method. The relevant electron paramagnetic resonance characteristics were investigated. The ferromagnetic and paramagnetic phase transition temperatures were determined by the magnetisation vs temperature M-T curves. The unique electrical transport properties originated from the coexistence of metal and insulator, ferromagnetic, and paramagnetic components in a given temperature range.

Hybrid graphene-manganite thin film structure for magnetoresistive sensor application

An increasing demand of magnetic field sensors with high sensitivity at room temperatures and spatial resolution at micro-nanoscales has resulted in numerous investigations of physical phenomena in advanced materials, and fabrication of novel magnetoresistive devices. In this study the novel magnetic field sensor based on combination of a single layer graphene (SLG) and thin nanostructured manganite La0.8Sr0.2MnO3 (LSMO) film—hybrid graphene-manganite (GM) structure, is proposed and fabricated. The hybrid GM structure employs the properties of two materials—SLG and LSMO—on the nanoscale level and results in the enhanced sensitivity to magnetic field of the hybrid sensor on the macroscopic level. Such result is achieved by designing the hybrid GM sensor in a Wheatstone half-bridge which enables to employ in the device operation two effects of nanomaterials—large Lorentz force induced positive magnetoresistance of graphene and colossal negative magnetoresistance of nanostructured manganite film, and significantly increase the sensitivity S of the hybrid GM sensor in comparison with the individual SLG and LSMO sensors: S = 5.5 mV T−1 for SLG, 14.5 mV T−1 for LSMO and 20 mV T−1 for hybrid GM at 0.5 T, when supply voltage was 1.249 V. The hybrid GM sensor operates in the range of (0.1–2.3) T and has lower sensitivity to temperature variations in comparison to the manganite sensor. Moreover, it can be applied for position sensing. The ability to control sensor’s characteristics by changing technological conditions of the fabrication of hybrid structure and tuning the nanostructure properties of manganite film is discussed.

Synthesis, morphological, optical properties of functionalized La0.33Ca0.67MnO3 for antibacterial therapy

A functionalized paramagnetic manganite La0.33Ca0.67MnO3 was investigated for its morphological, optical and antimicrobial properties. The manganite was capped by using a citrate ligand. The UV-visible spectrophotometer was used in monitoring the optical bands of the metal-citrate complex. It was observed to absorb in the visible region. The metal-citrate was reacted with a biologically active ligand (N-(3-nitrophenyl)-3-phenyl-2-(phenylsulfonamido) propanamide). The optical bands observed from the metal-citrate were used in monitoring the reaction between the metal-citrate and N-(3-nitrophenyl)-3-phenyl-2-(phenylsulfonamido) propanamide). The morphological property of the product formed was determined using SEMEDAX. The effect of the complex formed on the organic ligand, N-(3-nitrophenyl)-3-phenyl-2-(phenylsulfonamido) propanamide) was determined using 1H and 13C NMR. The bacterial inhibitory property of the metal-citrate-N-(3-nitrophenyl)-3-phenyl-2-(phenylsulfonamido) propanamide) complex was determined against Pseudomonas aeruginosa and Staphylococcus auerus. It was observed to inhibit the growth of Staphylococcus aureus only. The biological activities of the metal-citrate N-(3-nitrophenyl)-3-phenyl-2-(phenylsulfonamido) propanamide) suggest its use as an alternative antibacterial therapy.

Negative Magnetic Entropy Change and Critical Behavior of Manganite La0.8Sr0.2Mn1−xCoxO3 (x = 0, 0.2)

La0.8Sr0.2Mn1−xCoxO3 (x = 0, 0.2) polycrystalline samples were prepared by solid-state reaction, and their structural, Griffiths phase, magnetic entropy change, critical behavior, and electrical transport properties were systematically investigated. The results show that all polycrystalline samples are rhombohedral symmetry structures; the Griffiths phase exists above the low-temperature magnetic transition temperature (TC2) of the two samples; the magnetic field is applied to the La0.8Sr0.2Mn1−xCoxO3 (x = 0, 0.2) samples. The maximum magnetic entropy change ΔSmax for 7 T is − 2.28 and − 2.36 J/(kg K), respectively. The doping of Co makes ΔSmax increase, and an obvious negative entropy change occurs at low temperature and low field; the critical behavior of La0.8Sr0.2MnO3 (LSMO) fits best with the mean field model, and the critical behavior of the sample after doping with the 3D Heisenberg model fits best; LSMO is a semiconductor material, and the metal insulator transition appears near the low-temperature magnetic transition temperature (TC2) when the Co element doping amount reaches 0.2. The conductivity of the two samples in the high-temperature region satisfies the small polaron model.

Near-room-temperature magnetocaloric effect in electron-doped manganite probed by local atomic structure and critical exponent theory

Abstract Near-room-temperature and enhanced magnetocaloric properties are investigated for the chemical combustion synthesized electron-doped manganite La1−xZrxMnO3 with x = 0.05, 0.10 and 0.15. The single-phase rhombohedral crystal structure is observed particularly for the La0.90Zr0.10MnO3 (Zr10) system. Importantly, all the samples exhibit the paramagnetic-to-ferromagnetic (PM-to-FM) transition close to the room-temperature with the second-order phase transition. The analysis of the magnetic data in the critical region with different theoretical models such as 3D-Heisenberg, 3D-Ising, Mean-field, and Tri-critical mean-field suggested that the Zr10 sample exhibits the typical 3D-Heisenberg ferromagnetic characteristics. This indicated that the enhanced magnetic and magnetocaloric properties are governed by short-range exchange forces. Furthermore, the obtained data is also fitted with the Kouvel-Fisher method to obtain the transition-temperature, critical exponent β and it is found that the transition temperature and β values are totally consistent to that of the 3D-Heisenberg model. Significantly, the change in entropy |ΔSm| at 5 T is calculated to be 4.04 J·kg−1·K−1 at 304 K in case of Zr10 sample indicating that it can be one of the potential material for the future magnetic refrigeration technology working at near room-temperature.

Magnetic properties and magnetic entropy change of perovskite manganites La0.9–xEuxSr0.1MnO3 (x=0.000, 0.075) by experimental method and numerical fitting

Polycrystalline samples La0.9-xEuxSr0.1MnO3 (x = 0.000, 0.075) were prepared by the standard solid-state reaction method. The results show that the samples preform a characteristic of clusters spin-glass state at low temperature. The samples show a characteristic of ferromagnetism (FM) characteristic in the temperature range of 15–125 K and 15–150 K respectively; the samples show preformed clusters in the temperature range of 125–343 K and 150–325 K, respectively, the samples show paramagnetism (PM) characteristic above 343 and 325 K, respectively. The second-order transitions are found at 118 and 135 K for undoped and doped sample, respectively. When the applied magnetic field is 7 T, the maximum magnetic entropy change |ΔSM| value of the samples is near the Curie temperature (TC), and the value of |ΔSM| reaches 2.76 and 3.03 J/(K·kg), respectively. In addition, the relative cooling power (RCP) is found to be 425.28 and 443.53 J/kg. The numerical fitting data fit well with experimental data. These results indicate that both the samples have the potential to realize magnetic refrigeration in the high temperature region (T > 77 K).

Robust electronic phase separation on nanoscale of perovskite manganite La0.825Sr0.175MnO3

Electronic phase separation (EPS) plays a key role in elucidating the effects of complexity on emergent behavior for correlated electronic materials. In this work, we thoroughly studied a robust EPS existed in perovskite manganite La0.825Sr0.175MnO3. Results show that a typical paramagnetic-ferromagnetic (PM-FM) phase transition and a metallic-insulating phase transition occur at 285.4 and 295 K, respectively. Electron paramagnetic resonance (EPR) spectroscopy confirms that there are a double peaks rather than a single peak structures in the temperature region of 290 K≤T≤315 K, indicating that an obvious EPS state generates in this compound. Based on the variation of EPR intensities, we found that the FM composition continues to increase with the decrease of temperature in the whole EPS region. Moreover, it causes a percolative-like metallic-insulting transition when the percolative threshold approach ∼22.63% which is nearly equivalent to 25.34% obtained by calculating the ratio of spontaneous magnetization against theoretical saturated magnetization. Detailed phase diagram shows that the EPS state not only occupies most of PM region but also a state of multiphase coexistence is also found.