STO Substrates Research Articles

An experimental analysis of strontium titanate ceramic substrates polished by magnetorheological finishing with dynamic magnetic fields formed by rotating magnetic poles

Strontium titanate (SrTiO3, STO) ceramic substrate is an incipient ferroelectric material with a perovskite structure and which has a wide range of applications in the fields of microwave, millimetre wave, and optic fibre. This paper reports on a system of experiments carried out on STO substrates using a new magnetorheological (MR) finishing process where dynamic magnetic fields are formed by magnetic poles rotate. The results show that a circular ring shaped polishing belt with a stability evaluation zone appears on the surface after being polished by MR finishing with a single-point dynamic magnetic field. The dynamic magnetic fields are stronger when the revolutions of magnetic pole increase and eccentricity of pole enlarge, with the surface finish is smoother and more material is removed. The optimum machining times, machining gap, oscillation distance, eccentricity of pole, revolutions of the workpiece and magnetic pole are 60 min, 0.8 mm, 0 mm, 7 mm, and 350 r min−1 and 90 r min−1, respectively, and the best MR fluid consists of 6 wt% of diamond abrasives in W1 particle size and 18 wt% of carbonyl iron powder in W3.5 particle size. A surface roughness of Ra and a material removal rate of 8 nm and 0.154 μm min−1 can be obtained in these optimum process conditions. Finally, the polishing mechanism for dynamic magnetic fields and the mechanism for removing material from STO ceramic substrates are discussed in detail.

Electronic coupling between a FeSe monolayer film and SrTiO3 substrate

Several experimental groups have reported superconductivity in single unit cell layers of FeSe on ${\mathrm{SrTiO}}_{3}$ and a few other substrates, with critical temperature ${T}_{c}$ reports ranging up to 100 K, and a variety of theoretical work has been done. Here we examine more closely the interaction of a single FeSe layer with a ${\mathrm{TiO}}_{2}$ terminated ${\mathrm{SrTiO}}_{3}$(001) (STO) substrate. Several situations are analyzed: the underlying ideal interface, the effect of $z$-polarized longitudinal optic $[\mathrm{LO}(\stackrel{\ifmmode \hat{}\else \^{}\fi{}}{z}$)] phonons in STO, electron doping of the STO substrate, substitution of Se by the bordering chalcogenides S and Te, and doping by adsorption of K on the FeSe surface. These results complement earlier studies of O and Se vacancies. The O ${p}_{y},{p}_{y}$ surface band of STO persists at the interface, and by sharing holes with the hole pocket of FeSe it plays a part in the behavior around the interface, initially by determining the Fe Fermi level lineup with the STO band gap. The $\mathrm{LO}(\stackrel{\ifmmode \hat{}\else \^{}\fi{}}{z})$ mode causes strong band shifts around the interface but the strength of coupling to the Fe bands cannot be obtained with our methods. Adsorption of 25% K (one K per four Fe) fills the small O interface hole pocket and donates the rest of the electrons to the Fe hole pockets, filling them.

Plasmonic assisted two wave mixing phenomenon for energy transfer in ferroelectric PZT film

Ferroelectric – photorefractive PZT thin films have been exploited to study the energy transfer using pump probe technique for the development of optical delay lines. Two-wave mixing has been studied for three different PZT thin film samples deposited using pulsed laser deposition (PLD) technique. Uniform distribution of gold micro-discs of 40 nm thickness and 120 μm diameter over the surface of PZT thin film plays a vital role in enhancing the two-wave mixing. This is due to the ferroelectric domains present in PZT thin film which get polarized as a result of excited surface plasmons at the Au-PZT interface. The dual effect leads to an enhanced energy transfer from pump to ‘Probe Beam’. The maximum two-wave mixing gain was found to be about 1.185 and 1.055 respectively for gold micro-discs patterned and bare PZT thin film deposited on STO substrate. In comparison, the PZT thin film covered completely with the gold overlayer does not show any significant two wave mixing gain due to the scattering of light by Au overlayer.

Oxygen transport in epitaxial SrTiO<sub>3</sub>/SrTi<sub>1 − <i>x</i></sub>Fe<sub><i>x</i></sub>O<sub>3</sub> multilayer stacks

Abstract. Nano-ionic materials made of strontium titanate (SrTiO3, STO) and solid solutions of strontium ferrite in STO (SrTi1 − xFexO3, STF) are grown on single crystalline STO substrates and characterized. Since STF exhibits an oxygen deficiency and, simultaneously, enables oxygen interstitial defects, a space charge area close to the STO | STF interface is present. Oxygen tracer diffusion experiments and impedance spectroscopy at temperatures from 500 to 700 °C and at oxygen partial pressure ranging from 10−3 to 10−23 bar confirm fast oxygen transport caused by enhanced ionic conductivity at the interface. There, an oxygen diffusion coefficient of 3. 4 × 10−10 m2 s−1 at 600 °C and a p type conductivity of about 360 S m−1 at 700 °C are calculated. Such structures open new options in design of nano-ionic materials for oxygen sensors and energy conversion at temperatures lower than those of conventional materials such as yttrium-doped zirconia.

Electrical property effect of oxygen vacancies in the heterojunction of LaGaO3/SrTiO3**Project supported by the National Basic Research Program of China (Grant No. 2013CB632506) and the National Natural Science Foundation of China (Grant Nos. 11374186, 51231007, and 51202132).

Density functional theory within the local density approximation is used to investigate the effect of the oxygen vacancy on the LaGaO3/SrTiO3 (001) heterojunction. It is found that the energy favorable configuration is the oxygen vacancy located at the 3rd layer of the STO substrate, and the antiferrodistortive distortion is induced by the oxygen vacancy introduced on the SrTiO3 side. Compared with the heterojunction without introducing oxygen vacancy, the heterojunction with introducing the oxygen vacancy does not change the origin of the two-dimensional electron gas (2DEG), that is, the 2DEG still originates from the dxy electrons, which are split from the t2g states of Ti atom at interface; however the oxygen vacancy is not beneficial to the confinement of the 2DEG. The extra electrons caused by the oxygen vacancy dominantly occupy the 3dx2−y2 orbitals of the Ti atom nearest to the oxygen vacancy, thus the density of carrier is enhanced by one order of magnitude due to the introduction of oxygen vacancy compared with the density of the ideal structure heterojunction.

Bipolar resistive switching and substrate effect in GdK2Nb5O15 epitaxial thin films with tetragonal tungsten bronze type structure

Ferroelectric compound GdK2Nb5O15 with tetragonal tungsten bronze type structure thin films were grown by pulsed laser deposition on (001)SrRuO3/SrTiO3 and (001)SrRuO3/LSCO/MgO substrates respectively, in the same experimental conditions. Structural properties were investigated using X-ray diffraction in different modes. θ–2θ diffraction shows a single crystalline SRO and GKN phases, with c-axis perpendicular to the substrate. Phi-scans show for both SRO and GKN an epitaxial cube-on-cube growth. Reciprocal space mapping (RSM) was performed on GKN to determine the in-plane lattice parameters, and showed that GKN grown on MgO is more constrained comparing to STO. Room temperature electrical properties were investigated using platinum (Pt) top electrodes. Results show that GKN thin films deposited on MgO and STO substrates are resistively switchable. It was found that the nature of the substrate affects strongly the resistance ratio: GKN on SRO/LSCO/MgO showed a large hysteresis comparing to GKN on SRO/STO. Resistance switching in GKN is attributed to the oxygen vacancies migration which can be controlled by the substrate or the frequency sweep.

Surface potential distribution of a LaAlO3 film on mixed termination SrTiO3

Scanning probe microscope (SPM) is used to investigate the morphology and the electric properties of the surface, as well as the interface, of LaAlO3/SrTiO3 (LAO/STO) films. To establish the physical properties of the heteroepitaxial oxide interface, we characterized single- and mixed-termination of the STO substrates by using nanoscopic measurements of the electric and the structural properties, as well as the LAO film grown on the mixed-terminated STO substrates. In the case of the LAO film grown on the low-miscut STO substrate, the surface potential only showed a difference at the step edge while the LAO film on the high-miscut STO substrate showed a considerable change in the surface potential distribution at the region in which step bunching has occurred. In the poling experiment, a significant rise in the surface potential difference is observed after writing of the DC bias.

In-plane strain modulated magnetization and magnetoelectric effect in La0.7Sr0.3MnO3-BaTiO3 and La0.7Sr0.3MnO3-BaTiO3-BiFeO3 multilayer's

La0.7Sr0.3MnO3-BaTiO3(LSMO/BTO) and La0.7Sr0.3MnO3-BaTiO3-BiFeO3 (LSMO/BTO/BFO) multilayer thin films are deposited on STO (100) substrate by pulsed laser deposition. In-plane lattice mismatch induced strain is thoroughly investigated with the conclusion, that upper BTO layer of bilayer resides in high strained state, while upper BFO layer of trilayer remains under partially relaxed state. Significantly higher value (∼20) of dielectric constant is observed for LSMO/BTO bilayer in compliance with its higher (12.28 μC/cm2) in-plane strain induced interfacial polarization, which exceeds (2.06 μC/cm2), the observed value of polarization for LSMO/BTO/BFO trilayer. In LSMO/BTO bilayer, antiferromagnetic LSMO phase coexists due to the existence of strong tensile strain between the interfaces, which causes the reduction in value of saturation magnetization up to 50.76 emu/cm3 in comparison to 145.01 emu/cm3 for LSMO/BTO/BFO trilayer. The maximum value of linear magnetoelectric coefficient (α31) observed for LSMO/BTO bilayer is 24.77 mV/cm-Oe, which is higher in comparison to 19.54 mV/cm-Oe for LSMO/BTO/BFO trilayer, where the upper layer undergoes less strain in comparison to the bilayer.

Graphene/SrTiO3 hetero interface studied by X-ray photoelectron spectroscopy

The present paper focuses on study of graphene and strontium titanate (SrTiO3 or STO) interface. An ambient pressure chemical vapour deposition (AP-CVD) setup is used to grow graphene on STO (110) substrates in the presence of methane, argon and hydrogen gases at 1000°C for 4h. Raman spectroscopy measurements confirm the presence of graphene on STO substrates due to the existence of typical D and G peaks referring to graphene. These characteristic peaks are missing in the spectrum for bare substrates. X-ray photoelectron spectroscopy (XPS) is carried out for elemental analysis of samples, and study their bonding with STO substrates. We employed the valence band spectrum to calculate the valence band offset (VBO) and conduction band offset (CBO) at the G-STO interface. Also, we present an energy band diagram for Bi-layer and ABC (arranging pattern of carbon layers) stacked graphene layers.

Thermodynamic conditions during growth determine the magnetic anisotropy in epitaxial thin-films of La0.7Sr0.3MnO3

The suitability of a particular material for use in magnetic devices is determined by the process of magnetization reversal/relaxation, which in turn depends on the magnetic anisotropy. Therefore, designing new ways to control magnetic anisotropy in technologically important materials is highly desirable. Here we show that magnetic anisotropy of epitaxial thin-films of half-metallic ferromagnet La0.7Sr0.3MnO3 (LSMO) is determined by the proximity to thermodynamic equilibrium conditions during growth. We performed a series of x-ray diffraction and ferromagnetic resonance (FMR) experiments in two different sets of samples: the first corresponds to LSMO thin-films deposited under tensile strain on (0 0 1) SrTiO3 by pulsed laser deposition (PLD; far from thermodynamic equilibrium); the second were deposited by a slow chemical solution deposition (CSD) method, under quasi-equilibrium conditions. Thin films prepared by PLD show fourfold in-plane magnetic anisotropy, with an overimposed uniaxial term. However, the uniaxial anisotropy is completely suppressed in the CSD films. This change is due to a different rotation pattern of MnO6 octahedra to accommodate epitaxial strain, which depends not only on the amplitude of tensile stress imposed by the STO substrate, but also on the growth conditions. Our results demonstrate that the nature and magnitude of the magnetic anisotropy in LSMO can be tuned by the thermodynamic parameters during thin-film deposition.

The Electrical Properties of Epitaxial Grown Sc-Doped (Na<sub>0.</sub><sub>8</sub><sub>5</sub>K<sub>0.15</sub>)<sub>0.5</sub>Bi<sub>0.5</sub>TiO<sub>3</sub> Thin Film Prepared by Sol-Gel Method

Sc-doped (Na0.85K0.15)0.5Bi0.5TiO3 (NKBT-Sc) thin film was deposited on electrical conductive Nb-doped SrTiO3 [100] (Nb:STO) single crystal substrate via an aqueous sol–gel method. Structure analysis by x-ray diffraction and high resolution transmission electron microscopy proves the epitaxial growth relationship between the NKBT-Sc thin film and Nb:STO substrate. Well saturated ferroelectric hysteresis loops with remnant polarization of 26.14 μC/cm2 and typical butterfly shape displacement–voltage loop with effective piezoelectric coefficient d33* of 92 pm/V were observed, which were much higher than the NKBT-Sc thin film deposited on platinized silicon substrate. The precision LCR Meter exhibits a butterfly shape of dielectric constant and electric field curve, which is typical nature for the ferroelectric characteristics of the [001]-epitaxial NKBT-Sc thin film.

Engineering interfacial energy profile by changing the substrate terminating plane in perovskite heterointerfaces

Atomically engineered oxide heterointerfaces show a range of novel phenomena not present in their bulk form, thus providing an additional knob to tune the functional properties across such interfaces. Here we show that for an oxide Schottky interface between metallic SrRuO 3 and semiconducting Nb doped SrTiO 3 (Nb:STO) the terminating surface of the substrate plays a crucial role in determining the electronic transport across it. Interestingly this is achieved by engineering a monolayer of a charge-neutral SrO layer across the Schottky interface and not by the insertion of charged layers at the interface, as has been demonstrated earlier. These changes in the energy-band line-up across a symmetric interface indicate the presence of different polar characters at the SrO and TiO 2 terminations of the substrate. Owing to the presence of the same AO layer (SrO) in both SrRuO 3 and Nb:STO, we propose an intermixing of Ru and Ti ions across the interface for the SrO terminated Nb:STO substrate. First-principles density functional theory calculations on these systems conform with our experimental findings, and indicate a resultant shift in the interfacial atomic plane stacking of SrRuO 3 at the intermixed interface, leading to a modification of the electrostatic potential at the interface. The interdependence between the interfacial band alignment to the local atomic plane displacement across an intrinsically nonpolar oxide heterointerface is a key mechanism in realizing novel electronic properties in oxide based devices.

Polarization effects on the interfacial conductivity in LaAlO3/SrTiO3 heterostructures: a first-principles study.

We studied the influence of uniaxial [100] strain (-1% to +1%) on the electron transport properties of a two-dimensional electron gas (2DEG) at the n-type interface of the LaAlO3/SrTiO3(LAO/STO) heterostructure (HS)-based slab system from the perspective of polarization effects via first-principles density functional theory calculations. We first analyzed the unstrained system, and found that the induced polarization toward the vacuum in the LAO film leads to a small charge carrier density on the order of 10(13) cm(-2) (less than the theoretical value of 3.3 × 10(14) cm(-2) from the superlattice-model-based polar catastrophe mechanism), which is in excellent agreement with the experimental values of oxygen-annealed LAO/STO HS samples. Upon applying [100] tensile strain on the STO substrate, we found a significant reduction of the induced polarization in the LAO film. This reduction weakens the driving force against charge transfer from LAO to STO, causing an increase in the interfacial charge carrier density. The uniaxial strain also leads to a decrease of the effective mass of interfacial mobile electrons, resulting in a higher electron mobility. These findings suggest that applying uniaxial [100] tensile strain on the STO substrate can significantly enhance the interfacial conductivity of the LAO/STO HS system, which gives a comprehensive explanation for experimental observations. In contrast, compressively strained LAO/STO systems show stronger LAO film polarization than the unstrained system, which reduces the interfacial charge carrier density and increases the electron effective mass, thus suppressing the interfacial conductivity.

Molecular beam epitaxy growth of multilayer FeSe thin film on SrTiO3 (001)

Single-layer FeSe film grown on SrTiO3(001) surface (STO surface) by molecular beam epitaxy has aroused a great research boom ever since the discovery of its huge superconductive energy gap which indicates a possible critical temperature (Tc) higher than the liquid nitrogen temperature. The interface enhanced superconductivity with a Tc above 100 K is revealed in an in situ electrical transport measurement by using a four-point probe installed in a scanning tunneling microscope (STM). Consequent research interest in multi-layer FeSe films grown on STO surface is also increasing. The quality of thick FeSe film, however, has not been well studied yet in previous studies, although it is related to the sample properties including superconductivity. Here, reflection high-energy electron diffraction (RHEED) is used to monitor the growths of multi-layer FeSe thin films on STO surface under different growth conditions. Combing the RHEED results with STM observations taken at various FeSe coverages, we find that the intensity evolution of the RHEED pattern in the early growth stage can be well explained by the step density model but not by the widely known facet model. The intensity evolution of the FeSe(02) diffraction streak exhibits a single-peak oscillation in the growing of the first layer of FeSe. As the oscillation does not depend on the grazing angle of the high-energy electron beam, the FeSe(02) diffraction streak is very suitable for calibrating the FeSe growth rate. In contrast, the intensity of the specular spot exhibits different evolution pattern when the grazing angle of electron beam is changed. It is found in STM observations that only at an appropriate substrate temperature and a growth rate can the high-quality multi-layer FeSe films be grown on STO substrates. If the growth temperature is too high, the FeSe molecules nucleate into islands so that FeSe films with various thickness values eventually come into being on the STO surface. If the growth temperature is too low, a different phase of FeSe film is formed. The optimal growth temperature is in a range from 400 ℃ to 430 ℃, within which a two-layer FeSe film grown at a low rate (0.15 layer/min) coveres the whole STO surface with a negligible number of small FeSe islands. In contrast, a larger growth rate is necessary for growing thicker FeSe film. This is because FeSe islands tend to come into form at steps when the growth rate is too low, which is more distinct in a thicker FeSe film. An STM image of 80-layer FeSe film grown under an optimal condition, i.e., the substrate temperature of 420 ℃ and the growth rate of 2.3 layer/min, shows that it is in a perfect layer-by-layer growth mode. These experimental results are useful for growing high-quality multi-layer FeSe films on STO substrates, which could be critical for studying their physical properties and relevant physical phenomena.

Two-Dimensional Electron Gas at SrTiO3-Based Oxide Heterostructures via Atomic Layer Deposition

Two-dimensional electron gas (2DEG) at an oxide interface has been attracting considerable attention for physics research and nanoelectronic applications. Early studies reported the formation of 2DEG at semiconductor interfaces (e.g., AlGaAs/GaAs heterostructures) with interesting electrical properties such as high electron mobility. Besides 2DEG formation at semiconductor junctions, 2DEG was realized at the interface of an oxide heterostructure such as the LaAlO3/SrTiO3(LAO/STO) heterojunction. The origin of 2DEG was attributed to the well-known “polar catastrophe” mechanism in oxide heterostructures, which consist of an epitaxial LAO layer on a single crystalline STO substrate among proposed mechanisms. Recently, it was reported that the creation of 2DEG was achieved using the atomic layer deposition (ALD) technique, which opens new functionality of ALD in emerging nanoelectronics. This review is focused on the origin of 2DEG at oxide heterostructures using the ALD process. In particular, it addresses the origin of 2DEG at oxide interfaces based on an alternative mechanism (i.e., oxygen vacancies).

Creating Two-Dimensional Electron Gas in Nonpolar/Nonpolar Oxide Interface via Polarization Discontinuity: First-Principles Analysis of CaZrO3/SrTiO3 Heterostructure.

We studied strain-induced polarization and resulting conductivity in the nonpolar/nonpolar CaZrO3/SrTiO3 (CZO/STO) heterostructure (HS) system by means of first-principles electronic structure calculations. By modeling four types of CZO/STO HS-based slab systems, i.e., TiO2/CaO and SrO/ZrO2 interface models with CaO and ZrO2 surface terminations in each model separately, we found that the lattice-mismatch-induced compressive strain leads to a strong polarization in the CZO film and that as the CZO film thickness increases there exists an insulator-to-metal transition. The polarization direction and critical thickness of the CZO film for forming interfacial metallic states depend on the surface termination of CZO film in both types of interface models. In the TiO2/CaO and SrO/ZrO2 interface models with CaO surface termination, the strong polarization drives the charge transfer from the CZO film to the first few TiO2 layers in the STO substrate, leading to the formation of two-dimensional electron gas (2DEG) at the interface. In the HS models with ZrO2 surface termination, two polarization domains with opposite directions are in the CZO film, which results in the charge transfer from the middle CZO layer to the interface and surface, respectively, leading to the coexistence of the 2DEG on the interface and the two-dimensional hole gas (2DHG) at the middle CZO layer. These findings open a new avenue to achieve 2DEG (2DHG) in perovskite-based HS systems via polarization discontinuity.

Surface and grain boundary interdiffusion in nanometer-scale LSMO/BFO bilayer

Epitaxial 150nm thick LSMO/BFO bilayer is deposited on STO (100) substrate by pulsed laser deposition, to study magnetoelectric effect. Unexpected low value of room temperature magnetization in bilayer indicates towards the possibility of interdiffusion. Further, sharp fall in the value of TC (53K) also added our anxiety towards possible interdiffusion in BFO/LSMO system. Low-angle x-ray diffraction technique is used to investigate interdiffusion phenomena, and the temperature-dependent interdiffusivity is obtained by accurately monitoring the decay of the first-order modulation peak as a function of annealing time. It has been found that the diffusivity at different temperatures follows Arrhenius-type behavior. X-ray reflection (XRR) pattern obtained for the bilayer could not be fitted in the Parratt’s formalism, which confirms the interdiffusion in it. Depth profiles of 209Bi, 56Fe ions measured by secondary ion mass spectroscope (SIMS) further substantiate the diffusion of these ions from upper BFO layer into lower LSMO layer.

Thickness dependence of superconductivity and superconductor–insulator transition in ultrathin FeSe films on SrTiO3(001) substrate

Interface-enhanced high-temperature superconductivity in a one-unit-cell (UC) FeSe film on SrTiO3(001) (STO) substrate has recently attracted much attention in condensed matter physics and material science. Here, using ex situ transport measurements, we report on the superconductivity in FeSe ultrathin films with different thicknesses on STO substrate. We find that the onset superconducting transition temperature (Tc) decreases with increasing film thickness of FeSe, which is opposite to the behavior usually observed in traditional superconductor films. By systematic post-annealing of 5 UC FeSe films, we observe an insulator–superconductor transition, which is accompanied by a sign change of the dominant charge carriers from holes to electrons at low temperatures according to the corresponding Hall measurement.

Investigation of microstructure and magnetic properties of FePt–X films grown on MgO and STO substrates

Different thickness (001) textured FePt–X films were fabricated on MgO and SrTiO3 substrates, and the microstructure and magnetic properties of FePt–X films was systematically investigated. The study showed that the substrates with different lattice mismatch resulted in different crystallographic texture and microstructure. The larger mismatch strain with using MgO substrates would cause FePt films to follow the island growth mode, and the negligible mismatch strain with using STO substrate would form continuous film. Doping SiNx and C into FePt films caused the increase of lattice mismatch strain between FePt and MgO/STO, which would induce FePt films to forming island growth. The perpendicular anisotropy of FePt–SiNx–C films grown on MgO substrate was larger than that of using SrTiO3 substrate, which was attributed to the larger strain induced by larger lattice mismatch.

Influence of Lattice Strain on Phase Separation and Percolative Behaviors in La<sub>0.325</sub>Pr<sub>0.3</sub>Ca<sub>0.375</sub> MnO<sub>3</sub> Thin Films

The compressive and tensile strains induced by different substrates on La <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.325</sub> Pr <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.3</sub> Ca <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.375</sub> MnO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> (LPCMO) thin films have been investigated. It is found that the in-plane compressive strain favors the ferromagnetic metallic phase by increasing the hopping amplitude between neighboring elections and decreasing the tilt of the MnO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sub> octahedron, leading to the weakening of the phase separation. On the other hand, the in-plane tensile strain in films prefers to increase the stability of long-range charge/orbital ordering (COO) phase. Under 5 T magnetic field, the 30 nm LPCMO films on NGO and LSAT substrates show an obvious metal-insulator transition, indicating that the COO phase can be melted by the magnetic field at low temperature in the film with small in-plane tensile strain. The LPCMO film on STO substrate keeps insulating in the entire measuring temperature range even under 5 T magnetic field, suggesting that the COO phase in the film with a large tensile strain is more robust.