MnO3 Thin Films Research Articles

Integration of Both Invariable and Tunable Microwave Magnetisms in a Single Flexible La0.67Sr0.33MnO3 Thin Film.

High-quality flexible magnetic oxide thin films have promoted a wide range of potential applications in spintronic devices due to their unique physical properties. To obtain the optimized microwave magnetism for future all-oxide-based spintronic applications, high-quality oxide materials with excellent epitaxial quality as well as specific bending properties related to ferromagnetic resonance are high in demand. Here, (001)-oriented La0.67Sr0.33MnO3 epitaxial thin films with different thicknesses have been grown and subsequently transferred onto flexible poly(dimethylsiloxane) substrates. The microwave magnetisms of these film samples have been investigated under various bending states. Under bending, the ferromagnetic resonance lineshape of the film gradually transits from a single mode to a superposition of multimodes, possibly because of the uneven distribution of magnetization in the bending film at X-band. This phenomenon is more apparent when the direction of the applied magnetic field goes close to the out-of-plane of the film. Hence, an integration of invariable and continuous tuning of ferromagnetic resonance field under various mechanical bending can be achieved in one same sample by just tuning the direction of the applied magnetic field, which reveals that the flexible La0.67Sr0.33MnO3 thin films have huge potential in the applications in future flexible multifunctional devices.

Atomic replacement effects on the band structure of doped perovskite thin films

The potential applications of perovskite manganite R1-xAxMnO3 (R = rare earth element; A = Sr, Ca) thin films have been continuously explored due to their multi-functional properties. In particular, the optimally hole-doped La0.67Ca0.33MnO3 thin film demonstrates a colossal magneto-resistance that is beneficial to the performance of spintronic devices. To understand the effect of R and A ions on the material properties, we systematically measure the resistivity, magnetization, and electronic energy states for three optimally hole-doped R0.67A0.33MnO3 thin films with R = La, Sm and A = Sr, Ca. Various energy parameters are derived based on the X-ray absorption and X-ray photoelectron spectra, including the band gap, the charge frustration energy and the magnetic exchange energy. It is interesting to find that the replacement of La with Sm is more effective than that of Sr with Ca in terms of tuning the electrical property, the Curie temperature, and the band gap. The strain-induced reduction of the O 2p- Mn 3d hybridization and the interplay of R/A site disorder and strain effect are discussed. The results of this study provide useful information for the band design of perovskite oxide films.

Emergent Topological Hall Effect in La0.7Sr0.3MnO3/SrIrO3 Heterostructures.

Recently, perovskite oxide heterostructures have drawn great attention because multiple and complex coupling at the heterointerface may produce novel magnetic and electric phenomena that are not expected in homogeneous materials either in the bulk or in films. In this work, we report for the first time that an emergent giant topological Hall effect (THE), associated with a noncoplanar (NC) spin texture, can be induced in ferromagnetic (FM) La0.7Sr0.3MnO3 thin films in a wide temperature range of up to 200 K by constructing La0.7Sr0.3MnO3/SrIrO3 epitaxial heterostructures on (001) SrTiO3 substrates. This THE is not observed in La0.7Sr0.3MnO3 single-layer films or La0.7Sr0.3MnO3/SrTiO3/SrIrO3 trilayer heterostructures, indicating the relevance of the La0.7Sr0.3MnO3/SrIrO3 interface, where the Dzyaloshinskii-Moriya interaction due to strong spin-orbital coupling in SrIrO3 may play a crucial role. The fictitious field associated with THE is independent of temperature in La0.7Sr0.3MnO3/SrIrO3 heterostructures, suggesting that the NC spin texture may be magnetic skyrmions. This work demonstrates the feasibility of using SrIrO3 to generate novel magnetic and transport characteristics by interfacing with other correlated oxides, which might be useful to novel spintronic applications.

Thickness dependent uniaxial magnetic anisotropy due to step-edges in (1 1 1)-oriented La0.7Sr0.3MnO3 thin films

Abstract The magnetic anisotropy of films of La0.7Sr0.3MnO3 grown on vicinal (1 1 1)-oriented SrTiO3 substrates are investigated. For temperatures above the tetragonal – cubic structural phase transition temperature of the substrate, a step edge induced uniaxial magnetic anisotropy is found at remanence, with a thickness-driven change in easy axis direction, from perpendicular to the step edges to parallel to the step edges with increasing thickness. The anisotropy constant for the investigated (1 1 1)-oriented samples is of the same magnitude as for previously reported (0 0 1)-oriented samples. The data is discussed in the framework of in-plane rotations of the oxygen octahedra resulting in a uniaxial anisotropy. Furthermore, the magnetic anisotropy is sensitive to the structural phase transition at 105 K of the substrate, and the anisotropy constant increases drastically as the temperature is lowered below 105 K.

Néel vector reorientation in ferromagnetic/antiferromagnetic complex oxide nanostructures

In this study, we report on a temperature-driven antiferromagnetic (AF) spin reorientation transition in micro- and nanostructures of AF/ferromagnetic (FM) LaFeO3/La0.7Sr0.3MnO3 thin film bilayers. Using a combination of x-ray photoemission electron microscopy and x-ray absorption spectroscopy, the Néel vector is shown to reorient 90° as a result of the competition between a shape-imposed anisotropy in the AF layer and interface coupling to the adjacent FM layer. We demonstrate how a temperature dependence of the AF/FM spin configuration in line-shaped nanomagnets can be tuned by variation of their linewidth. This work provides insight into the AF/FM interface exchange coupling in complex oxide heterostructures and the possibilities of spin control by nanostructuring in thin film spintronics.

Free-standing La0.7Sr0.3MnO3 suspended micro-bridges on buffered silicon substrates showing undegraded low frequency noise properties

We report on the microfabrication process of free-standing suspended micro-bridges made of La0.7Sr0.3MnO3 (LSMO) thin films of thicknesses in the range of 10–100 nm. LSMO films were epitaxially grown on either SrTiO3 or CaTiO3 buffer layers on silicon substrates by reactive molecular beam epitaxy. The micro-bridges were patterned using standard UV photolithography then etched by ion beam and released using reactive ion etching of silicon in SF6. LSMO suspended micro-bridges 2 and 4 µm wide and of length ranging from 50 to 200 µm could be fabricated with a high fabrication yield (of about 85% as evaluated over 100 fabricated suspended micro-bridges) without degrading the electrical transport properties and in particular the low frequency noise level, as attested by the normalized Hooge parameter. The latter was measured in the 0.55–7.50 × 10−30 m3 range at 300 K, which is comparable to those measured in non-suspended high quality epitaxial LSMO thin films. This fabrication process could be useful for bolometer fabrication where thermal isolation is needed, or for any microelectromechanical systems devices making use of epitaxial functional oxides.

Oxygen vacancy induced electronic structure variation in the La0.2Sr0.8MnO3 thin film

Oxygen vacancy in different oxide systems shows up as a crucial parameter in modulation of the emerging application-oriented functionalities. A systematic exploration on the relation between oxygen vacancy and electronic structure of the La0.2Sr0.8MnO3 (LSMO) thin film has been carried out through sequential surface treatments followed by a series of wide scan XPS, O 1s XPS, O-K edge XAS, Mn-L edge XAS and work function measurements. Experimental results demonstrate mutual corroborative certifying evidences in between the different photoemission spectral measurements on the evolution and influence of the oxygen vacancy. Spectral characteristic features observed in the work are applicable using as justification fingerprint for the existence, modulation, or elimination of the oxygen vacancy in similar perovskite type oxide systems.

Current-controlled propagation of spin waves in antiparallel, coupled domains.

Spin waves may constitute key components of low-power spintronic devices. Antiferromagnetic-type spin waves are innately high-speed, stable and dual-polarized. So far, it has remained challenging to excite and manipulate antiferromagnetic-type propagating spin waves. Here, we investigate spin waves in periodic 100-nm-wide stripe domains with alternating upward and downward magnetization in La0.67Sr0.33MnO3 thin films. In addition to ordinary low-frequency modes, a high-frequency mode around 10 GHz is observed and propagates along the stripe domains with a spin-wave dispersion different from the low-frequency mode. Based on a theoretical model that considers two oppositely oriented coupled domains, this high-frequency mode is accounted for as an effective antiferromagnetic spin-wave mode. The spin waves exhibit group velocities of 2.6 km s-1 and propagate even at zero magnetic bias field. An electric current pulse with a density of only 105 A cm-2 can controllably modify the orientation of the stripe domains, which opens up perspectives for reconfigurable magnonic devices.

Engineering the magnetic order in epitaxially strained Sr1−xBaxMnO3 perovskite thin films

Chemical doping and epitaxy can be used to tailor the magnetoelectric properties of multiferroic thin films, such as SrMnO3. Here, we study the dependence of the magnetic order temperatures of Sr1−xBaxMnO3 thin films on epitaxial strain and Ba content. Combining low-energy muon spin spectroscopy and scanning transmission electron microscopy, the broadness of the magnetic transition is attributed to the presence of a Mn-O-Mn angle gradient along the out-of-plane direction. We also demonstrate that the unit cell volume is the key parameter to determine the Néel temperature in Sr1−xBaxMnO3 thin films showing G-type antiferromagnetic order. The occurrence of a simultaneously ferroelectric and ferromagnetic ground state at high strain levels is suggested for the Sr0.8Ba0.2MnO3 thin film deposited on TbScO3.

Electron-electron interactions in nano-patterned La0.3Sr0.7MnO3 thin films

Understanding the transport in ultrathin epitaxial La0.3Sr0.7MnO3 (LSMO) is a topic widespread current interest. Here, the authors explore electron-electron interactions in low temperature magneto-transport in straight and zigzag nanowires fabricated from ultrathin epitaxial LSMO films grown to different thicknesses on SrTiO3 (100) substrates. They find that three-dimensional electron-electron interactions can explain the resistivity upturn, including many changes observed with film thickness, nano-patterning, and magnetic field.

Magnetotransport Irreversibility in Single Crystalline La0.18Pr0.40Ca0.42MnO3 Thin Films

Magnetotransport irreversibility in single crystalline La0.18Pr0.40Ca0.42MnO3 thin films is probed with respect to intrinsic electronic phase separation (IEPS). Temperature‐dependent magnetization and resistivity measurements show that (i) the high temperature non‐hysteretic regime is dominated by the antiferromagnetic insulator (AFMI) and the charge ordered (CO) phases; (ii) at intermediate temperatures hysteretic regime is akin to a spin liquid; and (iii) the glass transition occurs at temperature Tg below which the spin liquid freezes. The suppression of the ferromagnetic and insulator–metal transitions (TC and TIM) during cooling confirms supercooled magnetic liquid. Magnetic field‐dependent resistivity (ρ–H) measured during cooling and warming highlights the differences in the spin‐ordered structures through (i) reversible behavior at T < Tg; (ii) colossal irreversibility in the isothermal cooling and warming ρ–H at Tg < T < TC/TIM; and (iii) reversible ρ–H at low/moderate fields but irreversible behavior at high fields at T > TIM (warming). The present study demonstrates that the scaling of area between the isothermal cooling and warming cycle ρ–H curves with temperature mimics the ρ–T behavior and hence also reflects the insulator–metal transition. The observed irreversibility and the area scaling in the different spin regimes have been explained in terms of the intrinsic electronic phase separation.

Temperature dependence of the magnetization of La0.67Sr0.33MnO3 thin films on LaAlO3

The authors report on the interplay between magnetically ordered phases with temperature and magnetic field across compressively strained interfaces of thin La0.67Sr0.33MnO3 films on LaAlO3 substrates. From the temperature dependence of the magnetization and resistivity studies, they find two distinct temperature regimes, where this interplay is clearly exhibited. They ascribe this to the strain induced Jahn–Teller-like distortion that favors the stabilization of the d3z2−r2 orbitals and enhances superexchange between adjoining Mn atoms. The temperature and field sweep of the magnetization and electronic transport lead to a hybridization between the closely spaced energy levels of d3z2−r2 and dx2−y2 orbitals leading to the coexistence of ferromagnetic and antiferromagnetic phases. Such an observation, not reported earlier, offers new routes for the design and study of magnetic textures in variously strained interfaces between perovskite oxides.

Strain induced extrinsic magnetocaloric effects in La0.67Sr0.33MnO3 thin films, controlled by magnetic field

The magnetic control of strain-induced giant caloric properties of epitaxial La0.67Sr0.33MnO3 (LSMO) thin films grown on (0 0 1) BaTiO3 (BTO) single crystal substrates is investigated. Arising from the crystallographic structural transformation of the BTO substrate during its 3-phase transitions, there is a drastic change of 3D film-lattice strain, which affects the local magnetic anisotropy of the LSMO at the interface and changes the entropy of the film. The thermal hysteresis observed in temperature dependent resistivity measurement can be manipulated by applying a magnetic field. Detailed transport and magnetic studies in different crystal orientations reveal the origin of such field-dependent magnetocaloric properties induced by the different phase transitions of the BTO substrate. Finally, a large entropy change of 1.03–1.95 J · Kg−1 · K−1 · T−1 was obtained at the monoclinic–tetragonal (M–T) transition at 283 K which compares to <1 J · Kg−1 · K−1 · T−1 for previously reported films.

Fabrication and ferromagnetic resonance study of BZT-BCT/LSMO heterostructure films on LAO and Pt

Abstract In this article, dynamic magnetic properties of La0.7Sr0.3MnO3 (LSMO) thin film capped with a Pb-free ferroelectric BZT-BCT layer deposited on two different substrates, i.e. lanthanum aluminate (LAO) and Platinum (Pt), by pulsed laser deposition (PLD) have been investigated using ferromagnetic resonance (FMR) spectroscopy. The heterostructures of BZT-BCT/LSMO on LAO substrate were highly (0 0 l)-oriented whereas these were randomly oriented on Pt substrate. The well-behaved M-H hysteresis loops were observed at room temperature for both heterostructures indicating the ferromagnetic behavior of LSMO. The right shift of the hysteresis loop of the heterostructure was observed due to the magnetoelectric coupling between ferroelectric and ferromagnetic layers. The FMR measurements yield optimum values of different important parameters such as the linewidth offset, Gilbert damping, gyromagnetic ratio, and in-plane uniaxial anisotropy field of the thin films, which are essential to design spin valve and magnetic tunneling based devices. We found the lowest Gilbert damping parameter of ∼0.03 for the BZT-BCT/LSMO/LAO heterostructure due to spin orbit coupling. In addition, the gyromagnetic ratio was also obtained to be small (0.002 GHz/Oe) in the same film. These results open new possibilities to use BZT-BCT/LSMO heterostructure for future spintronic device applications.

The role of cobalt doping on the optical and structural properties of Mn3O4 nanostructured thin films obtained by SILAR technique

Cobalt doped manganese oxide thin films (Mn3O4:Co) were successfully deposited on soda lime glass substrates using SILAR technique. Mn3O4:Co thin films were characterized using XRD, SEM, Uv–VIS and Raman spectroscopy. The XRD spectra showed that thin films had substantially Hausmannite crystal structure. The preferential orientation of the pure and 0.5 at.% Co doped manganese oxide thin films (Mn3O4) was (002), but with increasing Co doping, it was detected that this preferential orientation shift towards the (211) plane. The absorbance, transmittance and optical band gap of the Mn3O4:Co thin films were determined using Uv–Vis spectroscopy and these properties of the thin films differed considerably due to cobalt doping. The optical band gap of pure Mn3O4 thin films was 2.00 eV, but on the other hand, due to the Co doping this value increased before and then decreased slightly. Optical transmittance of Mn3O4:Co films increased from 60% to 72% with the effect of Co doping. A1g mode, which is the characteristic vibration peak of Mn3O4 films, was confirmed for pure and doped Mn3O4 thin films at a wavelength of 658 nm.

Microstructures and capacitance performance of MnO2 films fabricated by ultrasonic-assisted electrodeposition

Nanostructured MnO2 thin films were synthesized via an electrodeposition method assisted by ultrasonic treatment. Applying the ultrasonic treatment during or after electrodeposition, the films develop a variation of microstructures of distinct properties and characteristics. As a result, the MnO2 films show improved specific capacitances and cycling performance. The MnO2 film produced by electrodeposition followed by ultrasonic treatment exhibits a microstructure of free-standing nanowires with diameters less than 10 nm and the highest specific capacitance of 369 F g−1 in this investigation, which is fairly stable after successive cycles up to 1000 cycles. The enhanced capacitance performance of the MnO2 films suggests a great potential of the electrodeposition assisted by ultrasonic treatment for supercapacitor manufacturing.

The significant and temperature-insensitive magnetoresistance observed in Co-doped (La0.7Sr0.3)MnO3 thin films

Magnetic compounds with significant and temperature-insensitive magnetoresistance are quite promising for device applications. Here, we intentionally doped different amounts (0.025-0.1) of Co into epitaxial (La0.7Sr0.3)MnO3 thin films. The evolution of electrical, magnetic, magneto-transport, and valence state of this series of Co-doped (La0.7Sr0.3)MnO3 have been systematically characterized. Remarkably, the magnetoresistance in 0.1Co-doped (La0.7Sr0.3)MnO3 can reach significantly 35% within an extremely large temperature window (from 40 to 200 K). Other Co-doped epitaxial (La0.7Sr0.3)MnO3 thin films show similar sharp MR-peaks around Curie temperature as that in (La0.7Sr0.3)MnO3. The evolution of magnetic and magneto-transport properties of Co-(La0.7Sr0.3)MnO3 films can be explained by antiferromagnetic coupling induced by paramagnetic/low-spin Co3+(Co2+) ions in (La0.7Sr0.3)MnO3. Our work demonstrates that doping paramagnetic/low-spin Co into manganites is an effective way to optimize their magneto-transport properties.

Low temperature exchange bias study on Pr0.8Ca0.2MnO3/La0.3Ca0.7MnO3 system

Abstract Pr1-xCaxMnO3 with x = 0.2 is a ferromagnetic material at low temperature TC ∼ 130 K, and paramagnetic at higher temperatures, while La1-xCaxMnO3 with x=0.7 is antiferromagnetic material at low temperature TN ∼ 130 K. Bilayers with an antiferro/ferromagnetic (AF/FM) configuration based on manganites exhibit an interesting phenomenon known as exchange bias effect. Using a DC sputtering system at high oxygen pressure, we grew Pr0.8Ca0.2MnO3 (PCMO) and La0.3Ca0.7MnO3 (LCMO) thin films and Pr0.8Ca0.2MnO3/La0.3Ca0.7MnO3 (PCMO/LCMO) bilayers on (100) SrTiO3 substrates, to study the exchange bias effect in both systems (PCMO films and bilayers) at 10 K. Structural properties of samples were obtained by x-ray diffraction, reciprocal space maps, and transmission electron microscopy (TEM). Magnetic characterization was carried out by magnetic hysteresis loops measurements at 10 K. We found that PCMO thin films showed a shift in their hysteresis loops ∼80 Oe. However, the PCMO/LCMO bilayers displayed almost double of the shifting in the hysteresis loop ∼150 Oe. The additional shift with respect to the single layer could be associated to the interface interaction between PCMO and LCMO layers.

Investigation on Magneto Dielectric Properties of Y0.95Sr0.05MnO3/SNTO Thin Film Device

Abstract In this communication, Y0.95Sr0.05MnO3 (YSMO) thin film having a 300nm thickness, deposited on single crystal Nb:SrTiO3 (SNTO) substrate by pulsed laser deposition (PLD) technique, has been studied for its magnetodielectric and anisotropic properties. XRD measurement was performed for the YSMO/SNTO film which reveals the single phasic nature without any detectable impurity within the measurement range studied. To understand the possible anisotropic magnetodielectric behavior of the presently studied YSMO/SNTO film, frequency (20Hz - 2MHz) dependent dielectric constant was recorded at room temperature under zero field and 1T applied magnetic field dependent dielectric constant was recorded with two aspects: (i) field H parallel to the film's ab plane and (ii) field H perpendicular to the film's ab plane. Variation in the dielectric constant, as well as a magnetodielectric effect with applied magnetic field and field direction, has been discussed in detail.

Dynamic magnetic properties and spin pumping in polymer-assisted-deposited La0.92MnO3 thin films

Magnetic damping is enhanced in La0.92MnO3 thin films grown via polymer-assisted deposition by spin pumping in a Pt cap layer.