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The XANES spectra of the LaMnO 3Àd films grown under different oxygen pressures: (a) the K-edge and (b) the L II,III-edge spectra of Mn ions; (c) The L II,III-edge spectra of Mn ions in LSMO films. The dashed-dotted arrow line in (a) denotes the variation trend of the main peaks of the K-edge of Mn ions, and the vertical solid lines in (b) and (c) stand for the peak positions of the L III-edge spectra of Mn ions.
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The magnetic property of the LaMnO3−δ films was systematically investigated with the variation of the deposited oxygen pressure. The Curie temperature and the saturation magnetization of the films were found increased with the decrease of the oxygen pressure. We believe that the double exchange effect between Mn2+ and Mn3+ ions should be the origin...
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Citations
... We observe the presence of a ferromagnetic component for both as-grown and annealed samples, which is not expected for stoichiometric bulk LaMnO 3 but is similar to what has been reported previously in the literature for thin films. [22][23][24][25][26][27][28]33,34 The critical temperature is ∼125 K for the as-grown samples but increases to 150-225 K after annealing. The magnetic moment ranges from 0.75-1.2 ...
We present a detailed study of the magnetic, spectroscopic and structural properties of ultrathin LaMnO3 films deposited on SrTiO3(001) substrates by oxide molecular beam epitaxy. We find that the as-grown LaMnO3 films are slightly reduced and present a significant magnetic moment, while annealing to 600 °C fully oxidizes and enhances its magnetic properties. From synchrotron x-ray photoemission spectromicroscopy, we find the presence of Sr, Ca and Si in the LaMnO3 film that diffuse from the SrTiO3 substrate; these impurities act as hole dopants, and can explain the presence of ferromagnetism in LaMnO3. This work highlights the importance of cation mobility at the elevated growth temperature in modifying the magnetic properties of ultrathin LaMnO3 films.
... In addition, it is well known that oxygen vacancies doping is one of the important defects which is inevitable during the growth of oxide films. Its existence will significantly affect the valence state of metal ions and crystal structure of materials, thus changing various physical properties [16][17][18][19][20]. For example, if there are excessive oxygen vacancies in the lattice of YIG film, part of Fe 3+ in the material will be reduced to Fe 2+ , which will significantly affect the optical, magnetic and electrical properties [20,21]. ...
Oxygen vacancies doping in oxide materials is a very common means to modulate the electrical transport properties. In this work, Y3Fe5O12 (YIG) films with abundant oxygen vacancies were grown on Gd3Ga5O12 (GGG) substrates by solution spin coating and high vacuum annealing method, and the effect of oxygen vacancies on the electrical transport properties was systematically studied. It was found that a large amount of oxygen vacancies doping could convert the YIG film from a good room-temperature insulator to an electrical conductor. At high temperature and high vacuum, a large number of oxygen vacancies increased the disorder of the system, resulting in the appearance of a band-tail state, thus forming a constant range hopping conduction. While when the sample was exposed to air, the oxygen vacancies in the sample would gradually recombine and disappear, and the conduction mechanism transferred to drift mode.
... La 1Àx A x MnO 3 perovskites exhibit ferromagnetic properties 84,85 due to the double exchange interaction mechanism of Mn ions with different oxidation states. La 1Àx A x MnO 3 materials have attracted significant interest due to their giant magnetoresistance properties. ...
... The ferromagnetic properties and enhanced conductivity resulted from the formation of oxygen vacancies and Mn atoms with different oxidation states. 85 The doping of LaMnO 3 with Sr or Ca results in oxygen vacancies, which provide high diffusivity pathways for ions. 90,92 It was shown that the high oxygen vacancy mobility is an important factor for enhanced PC behavior. ...
Pseudocapacitive (PC) materials are under investigation for energy storage in supercapacitors, which exhibit exceptionally high capacitance, good cyclic stability, and high power density. The ability to combine high electrical capacitance with advanced ferrimagnetic or ferromagnetic properties in a single material at room temperature opens an avenue for the development of advanced magnetically ordered pseudocapacitive (MOPC) materials. This review covers materials science aspects, charge storage mechanisms, magnetocapacitance, and magnetoelectric (ME) phenomena in MOPC materials. Recent studies demonstrate high PC properties of advanced ferrimagnetic materials, such as spinel ferrites and hexagonal ferrites. Of particular importance is the discovery of PC properties of perovskite-type manganites, which exhibit room temperature ferromagnetism and giant negative magnetoresistance. The coupling of high capacitance and magnetization in MOPC provides a platform for strong ME interactions. Various strategies are used for manipulation of electrical capacitance/magnetization of MOPC by a magnetic field/electrode potential. Magnetocapacitance studies show significant increase in capacitance of MOPC under the influence of a magnetic field. Moreover, the application of a magnetic field results in enhanced energy density and power density, reduction of resistance, and improvement of cyclic stability. Such findings offer a potential of a breakthrough in the development of advanced supercapacitors. High magnetocapacitance and ME phenomena are linked to the influence of magnetic fields on electrolyte diffusion, structure of electrical double layer, charge transfer resistance, and variation of conductivity and magnetization of MOPC materials, which facilitate charge/discharge behavior. Various applications of ME effect in MOPC are discussed. Moreover, advantages of magnetocapacitive MOPC are described for applications in electronic and spintronic devices, supercapacitors, and devices for magnetically enhanced capacitive deionization of water.
... This strongly suggests that all these manganite/manganite interfaces (reported LMO/LCMO interface [18,44] as well as presently studied LMO/NSMO interfaces) are governed by higher thickness conducting manganite layers. However, it is also necessary to disclose here that upper 50 nm thin LMO layers in, both, reported LMO/LCMO/LAO structure [18,44] and present case of LMO/N-SMO/STO structures may experience oxygen deficiency (for the present case and [18,44,72]) or efficiency [73][74][75][76] supported zener double exchange mechanism thereby exhibit electronic phase transition from low temperature metal to high temperature insulator for a wide temperature window [72][73][74][75][76] [82] and La 0.67 Ca 0.33 MnO 3 ceramics [83]. All these studies indicate that the observed dual electronic phase transition has been ascribed to granular structure of the nanoparticles [77], simultaneous presence of tunneling effect and size effect within the nanoparticles [78], differently distributed grain interior and grain boundaries [79], spin dependent interfacial tunneling across the grain boundaries [80], strained and disordered grain surfaces/grain boundaries and related compositional inhomogeneities [81], inhomogeneous distribution of oxygen contents [82] and two phase structure, namely, bulk phase having intrinsic nature of transport and surface phase with inter--grain transport [83]. ...
... This strongly suggests that all these manganite/manganite interfaces (reported LMO/LCMO interface [18,44] as well as presently studied LMO/NSMO interfaces) are governed by higher thickness conducting manganite layers. However, it is also necessary to disclose here that upper 50 nm thin LMO layers in, both, reported LMO/LCMO/LAO structure [18,44] and present case of LMO/N-SMO/STO structures may experience oxygen deficiency (for the present case and [18,44,72]) or efficiency [73][74][75][76] supported zener double exchange mechanism thereby exhibit electronic phase transition from low temperature metal to high temperature insulator for a wide temperature window [72][73][74][75][76] [82] and La 0.67 Ca 0.33 MnO 3 ceramics [83]. All these studies indicate that the observed dual electronic phase transition has been ascribed to granular structure of the nanoparticles [77], simultaneous presence of tunneling effect and size effect within the nanoparticles [78], differently distributed grain interior and grain boundaries [79], spin dependent interfacial tunneling across the grain boundaries [80], strained and disordered grain surfaces/grain boundaries and related compositional inhomogeneities [81], inhomogeneous distribution of oxygen contents [82] and two phase structure, namely, bulk phase having intrinsic nature of transport and surface phase with inter--grain transport [83]. ...
... Khushal et al. [45] have also demonstrated that phase separation scenario is responsible for the dual electronic phase transitions observed for the resistance behavior recorded across the ZnO/LCMO interface of ZnO/LCMO/Al 2 O 3 heterostructure, prepared by using the same CSD method. By considering all these reports, present case of LMO/NSMO interface of LNP structure with the observed dual electronic phase transition behavior can be understood on the bases of (i) granular structure of LMO and NSMO manganite layers where (100) crystallographically oriented grains are present in both the manganite layers (XRD ω-scan rocking curves: Fig. 8; AFM images: Fig. 9) [77], (ii) inhomogeneous distribution of oxygen contents since LMO and NSMO manganite layers were prepared under different annealing environments [82], (iii) simultaneous presence of bulk (granular) and surface (boundary) phases (AFM images: Fig. 9) where grains behave as bulk phase that supports the intrinsic charge transport and grain boundaries behave as surface phase that holds the inter-grain transport [83] and (iv) differently behaved LMO (probably having comparatively lower temperature electronic phase transition [72][73][74][75][76] in the LMO/NSMO interface resistive behavior of Fig. 10) and NSMO (having comparatively higher temperature electronic phase transition in LMO/N-SMO interface resistive behavior in Fig. 10 [19,64,86]. As a consequence, NSMO manganite possesses better conduction across its lattice (thereby LMO/NSMO interface possesses comparatively lower resistivity) in LNP structure as compared to that in the case of LN11 structure (Fig. 10), (iv) NSMO manganite thin layer surface possesses lower rms surface roughness of ~2.76 nm in LNP structure as compared to that in LN11 structure (~6.32 nm). ...
... With the increase of I cc , more V O +/2+ drift from the top Pt/LaMnO 3 to the bottom Pt electrode and sufficient accumulation of V O +/2+ will lead to TS. V O +/2+ as extrinsic defects can be inserted into a target LaMnO 3 channel to alter conductivity and induce phase transition between the insulating and metallic phase without disrupting the crystal lattice framework [23]. In the oxygen-deficient LaMnO 3 thin film, the charge disproportionation effect is enhanced, which leads to an increase of Mn 2+ concentration [24]. The double exchange effect Mn 2+ -O-Mn 3+ occurs in the electron-doped LaMnO 3 films [25]. ...
The realization of highly efficient neuromorphic computing necessitates the development of fast artificial synapses devices. Mott insulator artificial synapses in particular provide tremendous potential for ultrafast neuromorphic devices. In this work, based on the Pt/LaMnO3/Pt heterostructures, a variety of synaptic plasticity has been realized, including paired-pulse facilitation/depression (PPF/PPD), spike rate-dependent plasticity (SRDP) and four types of spike time-dependent plasticity (STDP). Furthermore, Bienenstock-Cooper-Munro (BCM) learning rules with sliding frequency threshold have been found from SRDP. These findings make a great contribution to brain-like neuromorphic computing.
... For example, the double exchange of Mn 2+ − O 2− − Mn 3+ may occur more easily than the superexchange of Mn 2+ − O 2− − Mn 2+ due to the formation of an e g hole in Mn 3+ , which is in turn due to the lack of an electron in the 3d orbital [47]. Double-exchange interactions were introduced into perovskite oxides through element doping and oxygen vacancies to significantly improve the conductivity [32,[48][49][50][51]. Meanwhile, it has been shown that the regulation of the A/B-site ion radii can unfold the B-O-B bond and reduce the B-O bond length, which is beneficial to electron exchange interactions [44,52,53]. ...
High-entropy perovskite oxides (HEPs) are promising for supercapacitors and fuel cells. However, the obscure mechanism of the cocktail effect makes it challenging to simultaneously enhance the energy storage capability and oxygen reduction reaction. Herein, the cocktail effect is induced through an electronic structural design. Firstly, five non-equimolar elements are optimized in an HEP to achieve strong electron-electron couplings using Bi²⁺ and Fe²⁺ as electronic donors and Mn³⁺ and Cu²⁺ as electronic acceptors. These couplings form numerous double-exchange interactions for ultralong electron transport chains. Meanwhile, the large bond angle, short bond length, and G-type antiferromagnetic structure achieved in a yolk-shell La0.7Bi0.3Mn0.4Fe0.3Cu0.3O3 HEP lead to optimized electronic structures, which are suitable for accelerating the electron exchange interactions and promoting conductivity. Therefore, the yolk-shell La0.7Bi0.3Mn0.4Fe0.3Cu0.3O3 HEP shows a cocktail effect with the highest catalytic activity toward the oxygen reduction reaction in a 0.1 M KOH electrolyte as well as a substantial specific capacity of 480.95 C g⁻¹ at 0.5 A g⁻¹ in 6 M KOH. Finally, a material design idea for HEPs regulating ions as electronic donors and acceptors is proposed according to Hund’s rules to induce a cocktail effect caused by changes in the electronic structures, which is promising for supercapacitors, aqueous fuel cells and metal-O2 batteries.
... These peaks specify the presence of La-O, Sr-O, Mn-O bonds [35]. The O1s core level spectrum for PE sample (Fig. 5b) was also deconvoluted into three peaks. ...
Half-doped manganites has proven itself to be candid material for different magnetic-based devises. Various physical properties of pellet size half-doped La 0.5 Sr 0.5 MnO 3 manganite treated with oxygen plasma and its comparison with the pristine samples is reported in this article. The impact of plasma irradiation on different properties such as structure, thermoelectric power and electrical resistivity were studied and compared before exposure. The crystal structure or symmetry remains unaffected due to plasma exposure. The Mn 4+ /Mn 3+ ratio decreases after exposing to plasma compared to the pristine samples. It is observed that La 0.5 Sr 0.5 MnO 3 samples exhibit insulating behaviour before and after plasma exposure. The resistivity increases appreciably after plasma treatment which may be credited to the reduction in the bond angle of Mn-O-Mn as well as the creation of oxygen vacancies. The negativity of the thermopower is seen at all temperatures attributing it to the electrons behaving as the dominant charge carriers and also shows that the magnitude is temperature dependent.
... [31] The laser pulse with nanosecond and hundred mJ energy is irradiated onto the ceramic target surface and excites the ionized plasma out of the targets. The plasma is sputtered onto the heated single crystal substrates, as shown in Fig. 2(a), [44] and the sample can be subsequently har-088106-2 vested in the form of thin films, [45][46][47][48][49][50][51] heterostructures, [52][53][54][55] and superlattices. [56][57][58][59] Meanwhile, in order to identify the insitu growth process of low-dimensional structures, a variety of monitoring techniques have been elaborately developed, such as the oblique incidence reflectance difference, [60] surface photo-absorption, [61] spectral ellipsometry, [62] p-polarized reflectance spectroscopy, [63] and reflection high-energy electron diffraction (RHEED). ...
Photons with variable energy, high coherency, and switchable polarization provide an ideal tool-kits for exploring the cutting-edge scientific questions in the condensed matter physics and materials sciences. Over decades, extensive researches in the sample fabrication and excitations have employed the photon as one of the important means to synthesize and explore the low-dimensional quantum materials. In this review, we firstly summarize the recent progresses of the state-of-the-art thin-film deposition methods using excimer pulsed laser, by which syntactic oxides with atomic-unit-cell-thick layers and extremely high crystalline quality can be programmatically fabricated. We demonstrate the artificially engineered oxide quantum heterostructures exhibit the unexpected physical properties which are absence in their parent forms. Secondly, we highlight the recent work on probing the symmetry breaking at the surface/interface and weak couplings among nanoscale ferroelectric domains using optical second harmonic generation. We clarify the current challenges in the in-situ characterizations under the external fields and large-scale imaging using optical second harmonic generation. The improvements in the sample quality and the non-contact detection technique further promote the understanding of the mechanism of the novel properties emerged at the interface and inspire the potential applications, such as the ferroelectric resistive memory and ultrahigh energy storage capacitors.
... Due to the existence of oxygen vacancies, the conductivity of as-grown LMO film is greater than that of the antiferromagnetic insulating stoichiometric LaMnO3 film. In the oxygen-deficient LMO film, the eg electrons transmit between the Mn 2+ and Mn 3+ , resulting a conducting path [23]. In the initially nonpolarized state Pr 0 , the eight spontaneous polarization vectors of the PMN-PT crystal randomly point to the four body diagonals of the pseudo-cubic cell, corresponding to four structural domains (r1, r2, r3, and r4) [see the inset of Figure 1d]. ...
... Due to the existence of oxygen vacancies, the conductivity of as-grown LMO film is greater than that of the antiferromagnetic insulating stoichiometric LaMnO 3 film. In the oxygen-deficient LMO film, the e g electrons transmit between the Mn 2+ and Mn 3+ , resulting a conducting path [23]. In the initially nonpolarized state Pr 0 , the eight spontaneous polarization vectors of the PMN-PT crystal randomly point to the four body diagonals of the pseudo-cubic cell, corresponding to four structural domains (r1, r2, r3, and r4) [see the inset of Figure 1d]. ...
Multiferroic heterojunctions are promising for application in low-power storage and spintronics due to their magnetoelectric coupling properties. Controlling the magnetic and transport properties of magnetic materials by external stimuli and then realizing advanced devices constitute the key mission in this field. We fabricated a multiferroic heterostructure consisting of a ferroelectric single-crystal (001)-0.7Pb(Mg1/3Nb2/3)O3-0.3PbTiO3 substrate and an epitaxial 40 nm LaMnO3−x film. By applying dc electric fields to the ferroelectric substrate, the resistance and the photo-resistance of the LaMnO3−x film could be significantly modulated. With the electric field increasing from 0 to +4.8 kV/cm, the photo-resistance increased by ~4.1% at room temperature. The curve of photo-resistance versus the cycling electric field has a butterfly shape due to the piezoelectric strain effect. Using in situ X-ray diffraction measurements, the linear relationship of the strain and the electric field was quantitatively studied.
... Among reported FMI perovskite oxides, LaMnO 3 (LMO) is of particular interest due to its special features: LMO is antiferromagnetic in bulk form and ferromagnetic with T c ∼ 100 K in thin film form [12][13][14]. However, ferromagnetism of LMO films is delicate and considerably sensitive to doping or the sample preparation process because the process determines the content of inevitable oxygen vacancies [12][13][14][18][19][20][21][22]. Moreover, the distribution of such process-induced oxygen vacancies is inhomogeneous in LMO films, so ferromagnetic and antiferromagnetic regions coexist; as a result, the interfacial interaction between the ferromagnetic and antiferromagnetic regions leads to a weak exchange bias (EB) effect even in single LMO films [21]. ...
... However, the LMO diffraction peak is located right of the STO diffraction peak after postannealing the films in an oxygen atmosphere, indicating that the lattice constant of LMO shrinks to be smaller than that of STO. Since the lattice constant of the LMO film is reported to be sensitive to the oxygen vacancy content, more oxygen vacancies, and a larger lattice constant [18,21], this observation affirms that postannealing in an oxygen atmosphere can significantly suppress the oxygen vacancy content, which is beneficial for obtaining intrinsic and robust FMI in LMO films. Therefore, in this paper, the following investigations only focus on (1 − x)LMO:xCoO thin films postannealed in an oxygen atmosphere. ...
... When CoO is introduced into LMO matrix, on one hand, diffusion-induced local substitution of Co 2+ for Mn 3+ near the LMO/CoO interface is inevitable, leading to local ferromagnetism between Co 2+ and Mn 3+ [39]. On the other hand, charge transfer is expected between Mn 3+ and Co 2+ near the LMO/CoO interface, which leads to ferromagnetic interaction between Mn 3+ -Mn 2+ and Co 3+ -Co 2+ , etc [18,21,40], and more CoO content, stronger ferromagnetism. Actually, existence of Mn 2+ and Co 3+ is confirmed by XAS, as will be shown below. ...
Ferromagnetic insulators have received widespread attention for applications in novel low power consumption spintronic devices. Further optimizing the robust ferromagnetic insulating and developing multifunctional ferromagnetic insulator by integrating other magnetic property can not only ease or pave the way for actual application, but also provide an additional freedom degree for device designing. In this work, by introducing antiferromagnetic CoO into ferromagnetic insulator LaMnO3, we have constructed (1-x)LaMnO3:xCoO composite thin films. The films simultaneously show robust ferromagnetic insulator characteristics and large exchange bias. For x = 0.5 sample, the resistivity is 120 Ω·cm at 250 K while the magnetization is 100 emu/cm3 and the exchange bias field is -2200 Oe at 10 K. Especially, the blocking temperature is up to 140 K. Synchrotron radiation x-ray absorption spectroscopy reveals the coexistence of Mn3+, Mn2+, Co2+ and Co3+, arising from interfacial charge transfer and space charge/defect trapping, should be responsible for the enhanced and integrated multifunctional magnetic properties.
