La0.7Ca0.3MnO3 Research Articles

Enhanced magnetoresistance at wide temperature range in [Pr0.7Sr0.3MnO3/La0.5Ca0.5MnO3]20 superlattice on (001) MgO

[Pr0.7Sr0.3MnO3/La0.5Ca0.5MnO3]20 superlattices were epitaxially fabricated on (001) MgO substrates with 24 nm La0.5Ca0.5MnO3 (LCMO) buffer layer by pulsed laser deposition. As the thickness of Pr0.7Sr0.3MnO3 (PSMO) layer and LCMO layer is not identical, non-uniformity in the superlattice period thickness will occur and result in lower metal–insulator transition temperature and larger magnetoresistance (MR) at a wide low-temperature range. Furthermore, the percolation model was used to quantitatively understand the transport mechanism of superlattice. Our research results demonstrate that inhomogeneous layer thickness accompanied with charge ordering phase separation can strongly influence the transport properties of superlattice. Enhanced magnetoresistance at a wide temperature range provides possibilities for practical application in manganite-based film devices.

Enhanced near room temperature magnetocaloric effect in La0.6Ca0.4MnO3 for magnetic refrigeration application

Perovskite manganite La0.6Ca0.4MnO3 (LCMO) nanomaterials were synthesized by a modified Pechini sol–gel process followed by high temperature sintering.

Interface-enhanced sensitivity of photoconductivity to the electric current and magnetic field in La0.67Ca0.33MnO3/Nb-SrTiO3 p-n junctions

The effects of electric current and magnetic field on the photoconductivity (PC) of La0.67Ca0.33MnO3 (LCMO) films have been investigated within a comparative study on LCMO films on an n-type semiconducting Nb-doped SrTiO3 (NSTO) and insulating SrTiO3 (STO) substrates separately. At room temperature, LCMO on NSTO (LCMO/NSTO) was found to show remarkable PC effect than that on STO (LCMO/STO). More attractive is that, compared with that of LCMO/STO, the room-temperature PC of LCMO/NSTO also shows a high sensitivity to the change of current or magnetic field: for LCMO/NSTO under a light illumination with an intensity of 60 mW/cm2, the increment of current yields a decreases of PC at a rate of 7.6%/μA, while an application of magnetic field of 1.2 T can suppress PC by a percentage as high as ∼20%. In contrast, under the same stimulus of current or field, PC of LCMO/STO remains almost unchanged. The phenomena can be explained based on the interface effects correlated with the photocarrier injection, current shunting, and magnetic tunability occurred at the interface. This work demonstrates that manganite-based heterojunctions with interface engineering are promising for developing a new type of photoelectric device with high sensitivity and multifunctionality.

Interfacial Control of Ferromagnetism in Ultrathin La0.67Ca0.33MnO3 Sandwiched between CaRu1-xTixO3 (x = 0-0.8) Epilayers.

Controlling functionalities in oxide heterostructures remains challenging for the rather complex interfacial interactions. Here, by modifying the interface properties with chemical doping, we achieve a nontrivial control over the ferromagnetism in ultrathin La0.67Ca0.33MnO3 (LCMO) layer sandwiched between CaRu1-xTixO3 [CRTO(x)] epilayers. The Ti doping suppresses the interfacial electron transfer from CRTO(x) to LCMO side; as a result, a steadily decreased Curie temperature with increasing x, from 262 K at x = 0 to 186 K at x = 0.8, is observed for the structures with LCMO fixed at 3.2 nm. Moreover, for more insulating CRTO(x ≥ 0.5), the electron confinement induces an interfacial Mn-eg(x2-y2) orbital order in LCMO which further attenuates the ferromagnetism. Also, in order to characterize the heterointerfaces, for the first time the doping- and thickness-dependent metal-insulator transitions in CRTO(x) films are examined. Our results demonstrate that the LCMO/CRTO(x) heterostructure could be a model system for investigating the interfacial multiple interactions in correlated oxides.

Elastically strained and relaxed La0.67Ca0.33MnO3 films grown on lanthanum aluminate substrates with different orientations

Structure of 40-nm thick La0.67Ca0.33MnO3 (LCMO) films grown by laser evaporation on (001) and (110) LaAlO3 (LAO) substrates has been investigated using the methods of medium-energy ion scattering and X-ray diffraction. The grown manganite layers are under lateral biaxial compressive mechanical stresses. When (110)LAO wafers are used as the substrates, stresses relax to a great extent; the relaxation is accompanied by the formation of defects in a (3-4)-nm thick manganite-film interlayer adjacent to the LCMO-(110)LAO interface. When studying the structure of the grown layers, their electro- and magnetotransport parameters have been measured. The electroresistance of the LCMO films grown on the substrates of both types reached a maximum at temperature T (M) of about 250 K. At temperatures close to T (M) magnetoresistance of the LCMO/(110)LAO films exceeds that of the LCMO/(001)LAO films by 20-30%; however, the situation is inverse at low temperatures (T < 150 K). At T < T (M) , the magnetotransport in the grown manganite films significantly depends on the spin ordering in ferromagnetic domains, which increase with a decrease in temperature.

Structural, morphological, and magnetic properties of sol-gel derived La0.7Ca0.3MnO3 manganite nanoparticles

La0.7Ca0.3MnO3 (LCMO) manganite nanoparticles are synthesized via a sol-gel route at different annealed temperatures. Their structural, morphological, and magnetic properties are investigated. The X-ray diffraction patterns coupled with electron diffraction confirm that all the LCMO samples are single phase and crystallize in the orthorhombic perovskite structure (Pnma space group). The morphology of the samples observed by TEM, reveals a spherical shape with an average grain size lower than 50nm. The resolved lattice fringes in high-resolution TEM images also reveal the single crystalline nature of the LCMO nanoparticles. Magnetization measurements versus temperature under low magnetic field (0.01T) show a paramagnetic - ferromagnetic transition for all the samples. The Curie temperature (Tc) is found to be decreased with increasing the annealed temperature. A bifurcation is observed in the zero field-cooled and field-cooled magnetizations, indicating a competition between ferromagnetic and antiferromagnetic interactions in the nanoparticles at low temperatures. Field-cooled hysteresis measurements suggest a cluster glasslike behavior of the nanoparticles. Room temperature and low temperature M - H loops demonstrate that all the samples exhibit ferromagnetic behavior at 5K, whereas a paramagnetic behavior at room temperature. Resistivity behavior of the LCMO samples shows that they exhibit a metal - insulator transition. Magnetoresistance of ~ 50% at the field up to 8T was observed at 2K in the LSCO samples annealed at 600°C.

Electric field controlled magnetization and transport properties of La0.7Ca0.3MnO3 ultrathin film

We have investigated the effect of electric field on the magnetization in La0.7Ca0.3MnO3 (LCMO) ultrathin film (∼10 nm) by using it as the semiconductor channel material of a prototypical field effect device and SiO2 as dielectric gate. The direct magnetization measurements confirm the formation of a large ferromagnetic phase with the increase in the negative applied gate voltage. We have also shown that a large electroresistance (ER) of ∼78% with Vg = −8 V can obtained in LCMO by using a dielectric gate by reducing the thickness of the LCMO channel.

In-plane magnetic anisotropy of La0.7Ca0.3MnO3 film grown on (0001) sapphire

La0.7Ca0.3MnO3 (LCMO) films were grown on (0001) single-crystal sapphire (α-Al2O3) substrate by pulsed laser deposition. In this work, the growth of (110) oriented LCMO film on sapphire was achieved by controlling the film's deposition conditions, specifically the substrate temperature. The fixed orientation relationship between the film and the substrate [(110)f∥(0001)s, (1—10)f∥(01—10)s, (001)f∥(2—110)s], was measured by high-resolution X-ray diffraction (HRXRD) and grazing incident X-ray diffraction (GIXRD) techniques. The LCMO film showed interesting in-plane magnetic anisotropy along the two mutually perpendicular in-plane directions, corresponding to [001]f as strong and [1—10]f as weak magnetization directions.

Crossover from magnetostatic to exchange coupling in La0.67Ca0.33MnO3/YBa2Cu3O7/La0.67Ca0.33MnO3 heterostructures

The influence of YBa2Cu3O7 (YBCO) superconductor layer (S-layer) with a varying thickness dYBCO = 20–50 nm on the magnetic coupling between two La0.67Ca0.33MnO3 (LCMO) ferromagnet layers (F-layer, thickness dLCMO = 50 nm) in F/S/F heterostructures (HSs) was investigated by measuring global magnetization (M) in a temperature (T) range = 2–300 K and a magnetic field (H) range = 0–10 kOe. All the HSs were superconducting with the critical temperature (TC) decreasing from = 78 to 36 K with decrease in dYBCO, whereas the ferromagnetic ordering temperature TM = 250 K did not change much. Systematically measured M-H loops of all HSs at both T > TC and T < TC show three main results (a) the two step magnetic reversal above TC converts into a four step reversal below TC in HSs with dYBCO ⩾ 30 nm, (b) the magnitude and magnetic field corresponding to the additional two switching steps show characteristic evolution with T and dYBCO; and (c) the HS with dYBCO = 20 nm shows radically different behaviour, where the two step magnetic reversal above TC continues to persist below TC and converts into a single step reversal at T TC. The first two results indicate magnetostatic coupling between the magnetic domains and the vortices across the two F/S interfaces resulting in reversal dynamics different from that deep within the LCMO layers. Whereas, the result ‘c’ reveals indirect exchange coupling between LCMO layers through the superconducting YBCO layer, which is a clear experimental evidence of coexistence of ferromagnetism and superconductivity in nm scale F/S/F HSs expected theoretically by Sa de Melo (2003 Physica C 387 17–25).

Magnetic and electrical response of Co-doped La0.7Ca0.3MnO3 manganites/insulator system

We present a systematic study of the structural, magnetic and electrical properties of La0.7Ca0.3MnO3 (LCMO) and La0.7Ca0.3Mn0.95Co0.05O3 (LCMCO0 perovskite manganites. Most of the work is devoted to the electrical properties with a thorough discussion about different models for both the metallic and insulator states. With a view to understand the conduction mechanism in these materials, the resistivity of both materials was measured over a temperature range 5–300K and in a magnetic field up to 1T and the data were analysed by using several theoretical models. It has been observed that the metallic part of the temperature dependent resistivity (ρ) curve fits well with ρ=ρ0 +ρ2⊡5Τ2⊡5, indicating the electron–magnon scattering processes in the conduction of these materials. On the other hand, in the high temperature paramagnetic insulating regime, the adiabatic small polaron and VRH models fit well, thereby indicating that polaron hopping might be responsible for the conduction mechanism.

Superconductor to Mott insulator transition in YBa2Cu3O7/LaCaMnO3 heterostructures.

The superconductor-to-insulator transition (SIT) induced by means such as external magnetic fields, disorder or spatial confinement is a vivid illustration of a quantum phase transition dramatically affecting the superconducting order parameter. In pursuit of a new realization of the SIT by interfacial charge transfer, we developed extremely thin superlattices composed of high Tc superconductor YBa2Cu3O7 (YBCO) and colossal magnetoresistance ferromagnet La0.67Ca0.33MnO3 (LCMO). By using linearly polarized resonant X-ray absorption spectroscopy and magnetic circular dichroism, combined with hard X-ray photoelectron spectroscopy, we derived a complete picture of the interfacial carrier doping in cuprate and manganite atomic layers, leading to the transition from superconducting to an unusual Mott insulating state emerging with the increase of LCMO layer thickness. In addition, contrary to the common perception that only transition metal ions may respond to the charge transfer process, we found that charge is also actively compensated by rare-earth and alkaline-earth metal ions of the interface. Such deterministic control of Tc by pure electronic doping without any hindering effects of chemical substitution is another promising route to disentangle the role of disorder on the pseudo-gap and charge density wave phases of underdoped cuprates.

Ferromagnetic oxide heterostructures on silicon

Abstract

Comparative Study on Multifunctional Behaviors of La&lt;sub&gt;0.7&lt;/sub&gt;Ca&lt;sub&gt;0.3&lt;/sub&gt;MnO&lt;sub&gt;3&lt;/sub&gt; and La&lt;sub&gt;0.7&lt;/sub&gt;Ca&lt;sub&gt;0.24&lt;/sub&gt;Sr&lt;sub&gt;0.06&lt;/sub&gt;MnO&lt;sub&gt;3&lt;/sub&gt; Single Crystals

We report the electrical-transport, magneto-transport, and magnetic properties of the hole doped La0.7Ca0.3MnO3 (LCMO) and La0.7Ca0.24Sr0.06MnO3 (LCSMO) single crystals, prepared using floating zone technique. The resistivity data shows the metal to insulator transition (TMI) occurs at 211 K and 290 K for LCMO and LCSMO single crystals respectively. The electrical transport mechanisms of these crystals are investigated by using different theoretical models, for temperatures below and above TMI. The magnetization measurements show that these single crystals exhibit ferromagnetic to paramagnetic transition temperature (TC) at 208 K for LCMO and 273 K for LCSMO single crystals. From device application point of view, both samples show the maximum MR of 98% for LCMO and 80% for LCSMO at 8 T applied magnetic field, while for bolometer IR detectors application point of view the temperature coefficient of resistance (TCR) are found to ~17% K-1 and 28% K-1 for LCMO and LCSMO respectively.

Effects of strain on the magnetic and transport properties of the epitaxial La0.5Ca0.5MnO3 thin films

The epitaxial strain can considerably modify the physical properties of thin films compared to the bulk. This paper reports the effects of substrate-induced strain on La0.5Ca0.5MnO3 (LCMO) thin films, grown on (100) SrTiO3 (STO) and LaAlO3 (LAO) substrates by pulsed laser deposition technique. Transport and magnetic properties were found to be strongly dependent on strain type. It is also shown that compressive (tensile) strain leads to the increase (decrease) in the magnetization of the films. Moreover, it was observed that all LCMO films deposited on both LAO and STO substrates behave as an insulator, but LCMO/LAO thin films with compressive strain have lower resistivity than LCMO/STO thin films with tensile strain. Applying magnetic field to LCMO/STO thin films with thickness of 25 and 50nm leads to very small change in the resistivity, while the effects of magnetic field on the sample with thickness of 125nm leads to an insulator–metal transition. For LCMO/LAO thin films, the magnetic field has a strong impact on the resistivity of samples. The results show that the magnetoresistance (MR) is enhanced by increasing film thickness for LCMO/LAO samples, due to the relatively stronger phase separation. For LCMO/STO thin films MR is drastically decreased by reduction of film thickness, which is attributed to the enhancement of the charge–orbital order (CO–O) accompanying the complex spin order (the so-called CE type). The changes of the antiferromagnetic structure from the CE to C type and the enhancement of the CE type could be attributed to the in-plane compressive and tensile strain, respectively.

Sign reversal of angular dependence of Planar Hall Effect in La0.7Ca0.3MnO3/SrTiO3 ultrathin film

We have investigated the effect of strain on the transport and magnetic properties of La0.7Ca0.3MnO3 (LCMO) ultrathin films. Here, we present the observation of strain induced sign reversal of angular dependence of Planar Hall Effect (PHE) in LCMO ultrathin films (thickness ∼ 4 nm) deposited on SrTiO3 (001) substrate (STO). This observation of sign reversal in anisotropic magnetoresistance (AMR) was also reported by us (H. Sharma et al. APL, 105, 222406), previously. The sign reversal of AMR and angular dependence of PHE with magnetic field or temperature for the 4 nm thin film may be attributed to the increase in tensile strain in the plane of the thin film which in turn facilitates the rotation of the magnetization easy axis. High field or low field switching devices can be fabricated using these thin films.

Crystallographic direction dependence of electrical-transport, magneto-transport, magnetic and thermal properties of La0.7Ca0.3MnO3 single crystal

The crystallographic direction dependence of the electrical-transport, magneto-transport, magnetic and thermal properties of La0.7Ca0.3MnO3 (LCMO) single crystal along c-axis and ab-plane are investigated. The resistivity data shows the metal-insulator transition (TMI) occurs at 211K along c-axis and 185K along ab-plane. The electrical resistivity results are investigated by various theoretical models below and above TMI. The dc-magnetization shows ferromagnetic-paramagnetic transition (TC) at 208K along c-axis and at 190K along ab-plane. Moreover, ac-susceptibility and specific heat measurements reveal the phase transition temperature are in close agreement with the resistivity and magnetization measurements. To implement sensor application and data storage capacity, the temperature coefficient of resistance (TCR) and magnetoresistance (MR) are found to ⿼17% K⿿1 and 98% respectively.

Anisotropic transport properties in the phase-separated La0.67Ca0.33MnO3/NdGaO3 (001) films**Project supported by the National Basic Research Program of China (Grant Nos. 2011CB921801, 2012CB921403, and 2013CB921701) and the National Natural Science Foundation of China (Grant Nos. 11074285, 51372064, and 11134007).

The anisotropic transport property was investigated in a phase separation La0.67Ca0.33MnO3 (LCMO) film grown on (001)-oriented NdGaO3 (NGO) substrate. It was found that the resistivity along the b-axis is much higher than that along the a-axis. Two resistivity peaks were observed in the temperature dependent measurement along the b-axis, one located at 91 K and the other centered at 165 K. Moreover, we also studied the response of the resistivities along the two axes to various electric currents, magnetic fields, and light illuminations. The resistivities along the two axes are sensitive to the magnetic field. However, the electric current and light illumination can influence the resistivity along the b-axis obviously, but have little effect on the resistivity along the a-axis. Based on these results, we believe that an anisotropic-strain-controlled MnO6 octahedra shear-mode deformation may provide a mechanism of conduction filaments paths along the a-axis, which leads to the anisotropic transport property.

Electron transport behavior and charge ordering phenomena in La0.5Ca0.5MnO3

In this study, the polycrystalline sample of La0.5Ca0.5MnO3 (LCMO) with perovskite (Orthorhombic) crystalline structure was synthesized by citrate gel method. The temperature dependent magnetization studies exhibit both paramagnetic to ferromagnetic and ferromagnetic to antiferromagnetic transition of LCMO at ∼230 K and ∼150 K, respectively. The X-ray photoemission spectroscopy data revealed electronic structures, chemical properties, while the valence band photoemission spectra for LCMO measured at various photon energies ranging from 40 eV to 60 eV, showed Fano curve like resonance behavior for Mn 3p to 3d transition and also confirmed the change of DOS near Fermi level.

Current-Induced Reversible Resistance Jumps in La0.8Ca0.2MnO3 Microbridge**Supported by the National Natural Science Foundation of China under Grant Nos U1332205, 11404169 and 11274153, the Natural Science Foundation of Jiangsu Province under Grant No BK20140450, and the Huaian Science and Technology (Industry) Project under Grant No HAG2014043.

Two spatially confined La0.8Ca0.2MnO3 (LCMO) microbridges with different widths, starting from a single LCMO film (3 mm×5 mm), are fabricated by optical lithography. A second new and robust metal-insulator transition (MIT) peak at about 75 K appears, in addition to the normal MIT at 180 K observed in the standard LCMO film. When the two bridges are processed by currents of high densities, interesting reversible resistance jumps are excited only around the new peak. A stronger dependence of resistance jump on current excitation is found for the bridge with a smaller width. The temperature driven transition between new excited multiple metastable states are involved to explain the interesting low-temperature ultra-sharp jumps.

Fabrication and Characteristics of High- Superconducting/Magnetoresistive Mixed Sensors

Bicrystal grain boundary La0.7Ca0.3MnO3 (LCMO) tunneling magnetoresistance (TMR) mixed sensors with high- $T_{c}$ superconducting YBa2Cu3Oy (YBCO) transformers have been designed and fabricated. The mixed sensors show an increase in low-field magnetoresistance (MR) ratios at low temperatures and an increase in the slope of low-field MR curve at temperatures below superconducting critical temperature $T_{c}$ , indicating that the flux related to the field indeed can be captured by the superconducting YBCO loop with a constriction associated to the LCMO TMR junctions. Furthermore, the spin polarization parameter $P$ of 0.40 for LCMO at 10 K is obtained, and the temperature-dependent $P$ can be fitted by the curves of $P(T)\propto(T_{C}-T)^{0.97\pm 0.01}$ with $T_{C}=296 \text{K}$ . The temperature dependence of surface magnetization $M_{S}(T)$ deduced from $P(T)$ agrees with the theoretical models for $M_{S}(T)$ and leads to the conclusion that the charge carriers at the grain–interface boundary govern the tunneling conductivity for our bicrystal grain boundary junctions. In addition, the gain of mixed sensor as a function of temperature gets weaker as $T$ approaching $T_{c}$ . According to the voltage noise level of 6.8 $\mu\text{V/Hz}^{1/2}$ and the low-field slope of resistance variation $dR/dH\approx 781 \text{k}\Omega/\text{T}$ for the mixed sensor at 77 K, we obtain the field sensitivity ${S_{H}}^{1/2}$ of ∼0.58 $\mu{\text{T}/\text{Hz}}^{1/2}$ .