Some Important Features of Manganites

Manganites are very complex systems because of interplay among charge, spin, orbital and lattice degrees of freedom. To come closer to the understanding of its nature, we discuss its three important features: 1) correlation between magnetization and electrical resistivity in the same temperature range;2) detection of chemical constitution and the arrangement of Mn3+ and Mn4+ ions at different hole concentrations;and 3) how electrical current flows through double exchange in manganites. The first feature will be discussed for three-dimensional manganies. The features 2 and 3 are inscrutable in three-dimensional manganites. So they will be discussed for one-dimensional manganites and then generalized. One-dimensional solid has been discussed because it may give a see-through picture of various aspects of manganites. All the discussions will be done through a representative example of La1-xCaxMnO3, because it is the intermediate bandwidth manganite;has been most widely investigated and has the highest magnetoresistance. If two things: 1) magnetization and resistivity as a function of temperature at various magnetic fields;and 2) phase diagrams of other manganites are known, their properties can be understood by the discussion of the three features mentioned above.

Behavior of Mn^(2+) in perovskite manganites with nominal composition La_(0.6-x)Nd_xSr_(0.1)MnO_3

The fact that there are Mn^(2+) at the A sites in the ABO_3 perovskite phase of manganites with the nominal composition La_(0.6-x)Nd_xSr_(0.1)MnO_3 showed by detailed experimental study and theoretical calculations.The magnetic moments of these Mn^(2+) are antiparallel to those of the Mn ions at the B sites.The content of the Mn^(2+) increases as the average ionic radius,<r_A>,of the ions at A sites decreases,resulting in the experimentally observed phenomenon that the content of the Mn_3O_4 phase in the manganites decreases with decreasing <r_A>.

Magnetic and electronic properties of La-doped hexagonal 4H-SrMnO_(3)

As typical strongly correlated electronic materials, manganites show rich magnetic phase diagrams and electronic structures depending on the doped carrier density. Most previous relevant studies of doped manganites rely on the cubic/orthorhombic structures, while the hexagonal structure is much less studied. Here first-principles calculations are employed to investigate the magnetic and electronic structures of La-doped 4H-SrMnO_(3). By systematically analyzing the two kinds of La-doped positions, our calculations predict that the doped electron with lattice distortion would prefer to form polarons, which contribute to the local magnetic phase transition, nonzero net magnetization, and semiconducting behavior. In addition, the energy gap decreases gradually with increasing doping concentration, indicating a tendency of insulator–metal transition.

High-temperature synthesis and electronic bonding analysis of Ca-doped LaMnO_(3) rare-earth manganites

Doped lanthanum manganites La_(1-x)Ca_(x)MnO_(3) with five different concentrations of Ca(x=0.1,0.2,0.3,0.4 and 0.5) were synthesized by high-temperature solidstate reaction method and characterized.The prepared samples were experimentally analyzed by X-ray diffraction(XRD),ultraviolet-visible spectroscopy(UV-Vis),scanning electron microscopy/energy dispersive spectroscopy(SEM/EDS) and vibrating sample magnetometer(VSM)measurements.Orthorhombic structure is confirmed for this compound from powder X-ray diffraction data.The XRD data confirm the shrinkage in the unit cell of synthesized samples for increasing calcium concentration.The UV-Visible analysis for the estimation of optical band gap(E_(g)) reveals that the band gap decreases with the incorporation of Ca.The synthesized samples were investigated for charge density distribution using maximum entropy method,utilizing the XRD data sets.From the charge density analysis,it is found that the bond lengths for La-O and Mn-O bonds decrease with the addition of Ca.The ionic nature between La and O atoms and covalent nature between Mn and O atoms are enhanced for 40% of calcium-doping.For 50% of Ca-doped sample,ionic nature between La and O atoms and covalent nature between Mn and O atoms decrease.All the prepared samples exhibit ferromagnetism at 20 K and paramagnetism at 300 K.

A-site ordered state in manganites with perovskite-like structure based on optimally doped compounds Ln0.70Ba0.30MnO3（Ln=Pr,Nd）

In this paper,we report on the crystal structure and magnetic properties of the nano structured Baordered phases of rare-earth manganites obtained from the optimally doped solid solutions Ln0.70Ba0.30MnO3(Ln=Pr,Nd).The materials were studied by X-ray diffraction,scanning electron microscopy,energy dispersive spectroscopy and SQUID-magnetometry techniques.It is found that states with different degrees of cation ordering in the A-sublattice of the ABO3 perovskite can be obtained by employing special conditions of chemical treatment.In particular,reduction of the parent compounds results in the formation of a nanocomposite containing ferrimagnetic anion-deficient ordered phase LnBaMn2O5.Oxidation of the composite does not change an average size of the nanocrystallites,but drastically alters their phase composition to stabilize ferromagnetic stoichiometric ordered phase LnBaMn2O6 and ferromagnetic superstoichiometric disordered phase Ln0.90Ba0.10MnO3+δ.It is shown that the magnetic properties of the materials are determined by the joint action of chemical(cation ordering)and external(surface tension)pressures.

Spin-Dependent Electroresistance Behaviour of Nd_(0.67)Sr_(0.33)MnO_(3-δ) (0≤δ≤0.20)

Oxygen deficient Nd0.67Sr0.33MnO3-δ ceramic samples were prepared using conventional ceramic technology. A colossal electroresistance (CER) effect was found in Nd0.67Sr0.33MnO3-δ series. The electrical transport is magnetically coupled and spin-dependent over grain or phase boundaries. Electrical-field-induced changes of the spin array orientations inside of and between the magnetic domains by grain or phase boundaries have to be concluded for the strong electroresistive effect in Nd0.67Sr0.33MnO3-δ series.

Focused-Ion-Beam Induced Paramagnetic Defects in FAMn:PbI3 Perovskite Films

FAMn:PbI3 perovskite films were synthesized and probed mainly through electron spin resonance (ESR) spectroscopy. FAMn:PbI3 with low (~1%) Mn concentration showed a hyperfine sextet line originated from Mn++ ions. FAMn:PbI3 with high (10%) Mn concentration showed broad resonance (~500 G peak-to-peak linewidth). However, after bombardment of FAMn:PbI3 with high Mn concentration by focused ion beams (FIB), a sharp ESR peak appeared. The peak-to-peak linewidth (ΔHpp) was ~8 G regardless of the temperature. The FIB-induced defect showed Curie behavior at low temperatures (5 K - 50 K), which indicates the presence of localized electrons at the defect sites at low temperatures. The g-value increased from g = 2.0002 to 2.0016 as the temperature increased from 5 K to 50 K. Together with the ongoing search for electron spin echo (ESE), this could potentially provide a platform for realizing magnetic bits, information storage, and increased manipulation speed.

Review of photoinduced effect in manganite films and their heterostructures

Light–matter interaction plays an important role in the non-equilibrium physics, especially in strongly correlated electron systems with complex phases. Photoinduced effect can cause the variation in the physical properties and produce some emergent phases. As a classical archetype, manganites have received much attention due to their colossal magnetoresistance(CMR) effect and the strong interaction of charge, spin, orbital, and lattice degrees of freedom. In this paper, we give an overview of photoinduced effect in manganites and their heterostructures. In particular, some materials, including ZnO, Si,BiFeO_3(BFO), titanate-based oxides, and 0.7 Pb(Mg_(1/3) Nb_(2/3))O_3-0.3 PbTiO_3(PMN-PT) have been integrated with manganites. Heterostructures composed of these materials display some exciting and intriguing properties. We do hope that this review offers a guiding idea and more meaningful physical phenomena will be discovered in active areas of solid state physics and materials science.

Measurement and Analysis of Temperature Dependent Resistance of La0.67Ca/Sr0.33MnO3 CMR Samples Using LabVIEW

In this paper we report design of one virtual instrument for the measurement of resistance as a function of temperature. The program has been developed using the National Instruments’ graphical programming language ‘LabVIEW’ and has been run for the measurement of magnetoresistance of some colossal magnetoresistive (CMR) compounds, .

Influence of Photon Pump Fluence on Charge Carriers in FAPbI3 and Manganite Perovskites

FAPbI3 and FA(Mn:Pb)I3 perovskite films were prepared and evaluated through steady and transient absorption spectroscopy. According to the analysis using Elliot’s model, there were no considerable differences except for the absorption intensity between FAPbI3 and FA(Mn:Pb)I3 perovskite films: the value of the optical gap (Eg) and the position of exciton resonance (E0) were the same. The femtosecond transient absorption showed biexponential relaxation properties of the charge carriers, suggesting that biexcitons are more easily generated in FA(Mn:Pb)I3 than FAPbI3 perovskite. The generation of biexcitons in FA(Mn:Pb)I3 was also confirmed by the photon pump fluence dependence. Moreover, we were able to estimate the average number of absorbed photons directly from the photon pump power dependence without needing any further experimental measurements such as photoluminescence. Our findings may offer a new way of understanding photoinduced carrier dynamics in perovskite manganites.

Synthesis ofγ-MnOOH nanorods by successive ionic layer deposition method and their capacitive performance

It was first shown in the present study that layers of manganite γ-Mn OOH can be deposited on the surface of a substrate by its multiple successive treatment by the solutions of MnSO_4 and K_2S_2O_8 using the successive ionic layer deposition(SILD) technique. Their analysis was carried out by the XRD, XPS, FT-IR,SEM and EDX methods. It has shown that the synthesized layers are formed by aggregates of nanorods up to 80–100 nm in length and approximately 8–10 nm in diameter. A probable sequence of chemical reactions leading to the formation of a layer of the given morphology is suggested. Testing of performance of supercapacitors with nickel foam electrodes incorporating the γ-Mn OOH layers in the 0.1 M KOH electrolyte at 1 A/g indicated the specific capacitance equal to 1120 F/g. After 1000 work cycles the observed degradation of this value was less than 3%.

Electrochemical performance and stability of Sr-doped LaMnO_(3)-infiltrated yttria stabilized zirconia oxygen electrode for reversible solid oxide fuel cells

Porous Sr-doped lanthanum manganite–yttria stabilized zirconia(LSM–YSZ)oxygen electrode is prepared by an infiltration process for a reversible solid oxide fuel cell(RSOFC).X-ray diffraction and SEM analysis display that perovskite phase LSM submicro particles are evenly distributed in the porous YSZ matrix.Polarization curves and electrochemical impedance spectra are conducted for the RSOFC at 800 and 850C under both SOFC and SOEC modes.At 850℃,the single cell has the maximum power density of~726 mW/cm^(2)under SOFC mode,and electrolysis voltage of 1.35 V at 1 A/cm^(2)under SOEC mode.Fuel cell/water electrolysis cycle shows the cell has good performance stability during 6 cycles,which exhibits the LSM–YSZ oxygen electrode has high electrochemical performance and good stability.The results suggest that netw ork-like LSM–YSZ electrode made by infiltration process could be a promising oxygen electrode for high temperature RSOFCs.

Infrared Spectra of La_(0.65)Ba_xMnO_(3-δ) Oxides

The infrared spectra of La0.65BaxMnO(3-|?￡（c） （x = 0.35, 0.33 and 0.30） were investigated experimentally. The result shows that the sample La0.65BaxMnO(3-|?￡（c） has the largest Curie temperature and the smallest resistivity and wave number of the stretching vibration mode of MnO6 octaheUron at 300 K among the investigated samples. However, the absorption strength for the stretching vibration mode of Mn06 octahedron in La0.65BaxMnO(3-|?￡（c） is stronger for parainagnetic phase than that for ferromagnelic phase, which may be connected with the reducing of the dynamic in- coherent Jahn-Teller distortion below Curie temperature. In addition, the large shift of wave number for the stretching mode at the temperatures from 293 to 423 K has been observed in La0.65BaxMnO(3-|?￡（c）, which may be due to the in- crease of the Mn-O bond length with temperature increasing.

Enhanced room temperature magnetoresistance in maganites La_(0.60)Sr_(0.25-y)Na_(0.15)Δ_yMnO_(31)

Bulk polycrystalline samples of La0.60Sr0.4MnO3 and La0.60Sr0.25-yNa0.15ΔyMnO3 with 0.00≤y≤0.15 (“Δ” representing cation vacancy) were successfully synthesized using the sol-gel method. The structural, magnetic, and electrical properties of the polycrystalline of the samples were investigated. The results of X-ray powder diffraction patterns show that these compounds crystallize in a distorted rhombohedral structure with the space group R3C. The measurement shows that, with vacancy content y increasing, the unit cell volume V of samples increases, furthermore, the Curie temperature TC decreases. The temperature dependence of resistivity shows that all samples undergo a metal-semiconductor transition accompanying a ferromagnetic to paramagnetic transition with the increase of temperature. Under an applied filed of 1.8 T, a maximum room temperature magnetoresistance (MR) of 20% is obtained at 293 K for the compound La0.60Sr0.1Na0.15Δ0.15MnO3. The MR peak value of La0.60Sr0.1Na0.15Δ0.15MnO3 increases 2 times more than that of La0.60Sr0.40MnO3 (MRP=6.4%, TMR=373 K), and the MR peak is shifted from 373 K to room temperature.

Structural Analysis of a New Phase of BaNdMnO_4

Single crystal of BaNdMnO4 with I4/mmm was synthesized by a floating zone method. A new phase of BaNdMnO4 was obtained by annealing the single crystal in a reducing atmosphere at 573 K for 10 d. The structural change was analyzed by four-circle X-ray diffractometry and transmission electron microscopy. The new phase has an orthorhombic unit cell (Fmmm) of a=0.5486(2)nm, b=0.5484(2)nm, and c=1.3059(2)nm.

Novel Phase Transition in BaPr_2Mn_2O_7

The rare earth manganite BaLn2Mn2O7 (Ln=rare earth element) has a Sr3Ti2O7-type layered perovskite structure with double-block oxygen octahedra belonging to the Ruddlesden-Popper-type homologous series AO(ABO3)2. In Pr-manganite, a novel phase transition was first observed in situ at 1040 K by a thermal transmission electron microscope. At 1040 K, reflections began to split along the c-direction in the selected area diffraction pattern. This indicates that a new phase appears in the original phase matrix; the c length of the new phase is 1.5% longer than that of the original phase. After about 5 min, the original phase disappears. No change in the crystal symmetry (space group I4/mmm) is observed above 1040 K.

Anomalous Magnetic Behavior in Phase-separated La0.5 Sr0.5 MnO3 +δ Films

(001)La0.5 Sr0.5MnO3 +δ films on (001)LaA1O3 substrates were prepared by using a RF magnetron sputtering with powder target.At low temperature, the films exhibit two phase coexistence, which means that ferromagnetic (FM) clusters are embedded in antiferromagnetic (AFM) matrix.Moreover, a shift in hysteresis loop is unexpectedly observed in this inhomogeneous system.We suggest that the anomalous hysteresis loop may result from the unidirectional exchange anisotropy at the interface between AFM and FM clusters.

Structural and Magnetic Properties in Nd_(0.7)Sr_(0.3)MnO_3 Manganite

The temperature evolution of the crystal structure for Nd_(0.5)Sr_(0.5)MnO_3 has been investigated by powder XRD between 125 Kand 725K.The structure can be described with a monoclinic symmetry(space group P21/m)in the temperature range of 125—175 K,while with the increase in temperature between 175 Kand 575 Kthe structure involves a higher orthorhombic symmetry(space group Imma).The rhombohedral structure with space group R-3cis observed at high temperature region of 575—725K.The increase in the magnetization at low temperatures can be ascribed to the field-induced short-range magnetic order of the Nd3+ions.The dc and ac susceptibility data show some anomalies around the FM-PM transition region which can be attributed to the glass behavior and magnetic relaxation.

Visualization of tunnel magnetoresistance effect in single manganite nanowires

We reported a study of tunnel magnetoresistance(TMR)effect in single manganite nanowire via the combination of magnetotransport and magnetic force microscopy imaging.TMR value up to 290%has been observed in single(La1-yPry)1-x CaxMnO3 nanowires with varying width.We find that the TMR effect can be explained in the scenario of opening and blockade of conducting channels from inherent magnetic domain evolutions.Our findings provide a new route to fabricate TMR junctions and point towards future improvements in complex oxide-based TMR spintronics.

Magnetic Properties of Perovskite Manganite La_ (0.3)Ca_ (0.7)Mn_ (0.96)W_ (0.04)O_3 in Charge Ordering Phase

The sample La 0.3Ca 0.7Mn 0.96W 0.04O3 was prepared by the solid-state method. Magnetic properties of La 0.3Ca 0.7Mn 0.96W 0.04O3 was studied through the measurement of M-T curve, M-H curves and ESR curves of the sample. The results show that: charge ordering （CO） phase forms at 265 K; the system exhibits paramagnetism when T>265 K; it exhibits long-range anti-ferromagnetism （there is a little FM component in AFM background） and the coexistence of a little FM phase and AFM/CO phase forms when T<225 K; the system transforms from paramagnetism to antiferromagnetism in charge-ordering state with temperature decreasing from 265 to 225 K. The width of ESR spectrum line of the sample La 0.3Ca 0.7Mn 0.96W 0.04O3 was measured, and the value of the line width of paramagnetic resonance ΔH PP increases with temperature decreasing, which indicates that ferromagnetic connection of the sample strengthens with temperature decreasing.