Pr0.5Sr0.5MnO3 Research Articles

Magnetic Interactions with Strain Gradient in Ultrathin Pr0.67Sr0.33MnO3 Films

Strain gradient is a normal phenomenon around a heterostructural interface in ultrathin film, and it is important to determine its effect on magnetic interactions to understand interfacial coupling. In this work, ultrathin Pr0.67Sr0.33MnO3 (PSMO) films on different substrates are studied. For PSMO film under different in-plane strain conditions, the saturated magnetization and Curie temperature can be qualitatively explained by double-exchange interaction and the Jahn–Teller distortion. However, the difference in the saturated magnetization with zero field cooling and 5 T field cooling is proportional to the strain gradient. Strain-gradient-induced structural disorder is proposed to enhance phonon–electron antiferromagnetic interactions and the corresponding antiferromagnetic-to-ferromagnetic phase transition via a strong magnetic field during the field cooling process. A non-monotonous structural transition of the MnO6 octahedral rotation can enlarge the strain gradient in PSMO film on a SrTiO3 substrate. This work demonstrates the existence of the flexomagnetic effect in ultrathin manganite film, which should be applicable to other complex oxide systems.

Anomalous low-energy carrier dynamics of stripe-type charge ordered Pr0.5Sr0.5MnO3 thin film revealed by magneto-terahertz spectroscopy

The perovskite manganites host a range of charge- and orbital-ordered phases wherein the intrinsic and extrinsic controls of magnetic field, doping, epitaxial strain, chemical pressure, etc., induce subtleties of phase transition. The Pr0.5Sr0.5MnO3 (PSMO) is one such system that possesses a unique stripe-type charge-order manifesting in anisotropic transport. It exhibits a Drude-type and charge-density-wave (CDW) type of low-energy phases; the magnetic field is contemplated as a key control for both these phases; however, it has not yet been explored. Here, we have investigated the magnetic-field dependence of Drude-type terahertz (THz) carriers dynamics and the CDW type of low-energy excitations along two non-identical orthogonal in-plane axes of the (110) epitaxial thin film in the energy range of 1–7 meV using magneto-THz time-domain spectroscopy in Faraday geometry. While THz Drude conductivity expectedly increases with the increasing magnetic field, the CDW type of resonance absorption peak anomalously strengthens with the field. The origin of this unusual field-induced stabilization of the CDW-type mode is expected to lie in the d(x2–y2) orbital ordering in the A-type antiferromagnetic ordered state and anisotropic charge ordering. This study brings out a unique facet of the effect of magnetic field on orbital ordering of anisotropic stripe-type charge-ordered PSMO, which has potential THz modulation and switching applications.

Structural, electrical, and magneto-transport properties of Pr0.7Sr0.3MnO3: Al2O3 composites

Incorporation of insulating secondary phase into manganite composites can enhance the low-field magnetoresistance (LFMR). This work reports the structural and electrical transport properties of (1-x) Pr0.7Sr0.3MnO3 (PSMO): x Al2O3 composites synthesised by solid-state reaction method. X-ray diffraction (XRD) patterns indicated that Mn-O-Mn bond distance and angle were disturbed due to the substitution of Al3+ at Mn-site of PSMO system. This subsequently increased the resistivity of composite samples and shifted the metal-insulator transition temperature (TMI) to lower temperatures as increasing content of Al2O3. LFMR effect was observed as the magnetoresistance values increase monotonically with the decreasing temperature.

Colossal crystalline anisotropic magnetoresistance in A-type antiferromagnetic film

A colossal crystalline anisotropic magnetoresistance (CAMR) is observed in an epitaxial A-type antiferromagnetic Pr0.5Sr0.5MnO3 (PSMO) thin film, which is 1600% at 20 K under the magnetic field of 50 kOe. This colossal CAMR is associated with an anisotropic switching process between low and high resistivity states. Based on the symmetry of angular dependence of the CAMR, we attribute the origin to the strong anisotropic magnetostriction in PSMO. Our results explored a potential utilization of an A-type antiferromagnetic thin film for CAMR based spintronic devices.

Critical behavior investigated through magnetocaloric effect in PrSrMnO and Pr(Sr,Ca)MnO manganites

In this work we investigate the critical behavior of two manganite compounds, Pr0.5Sr0.5MnO3 (PSMO) and Pr0.5Sr0.41Ca0.09MnO3 (PSCMO). These are complex magnetic systems, which undergo a paramagnetic to ferromagnetic phase transition on cooling, followed by a first order magnetic transition to a charge ordered antiferromagnetic states at lower temperatures. Magnetization measurements and magnetocaloric calculations were performed in order to determine their critical behavior. As a main result we show that the scaling of the entropy change -ΔSM with magnetization M, instead of the usual scaling with magnetic field H, is a powerful tool to study the critical behavior through magnetocaloric analysis. We use this property, in conjunction with Modified Arrot Plot technique, to determine the basic critical exponents β and γ for each sample. The exponents values indicate that the samples are near to universality class models based in nearest neighbor interactions. Besides intrinsic differences between the Ca-doped and the undoped sample, we confirm the applicability of the magnetocaloric analysis in order to determine critical behavior in complex magnetic systems.

Investigation of Nano-Sized Al<sub>2</sub>O<sub>3</sub> on Pr-Sr-Mn-O Composites: Structural, Microstructural and Magnetic Properties

Perovskite manganites have always been the research interest attributed to its intriguing colossal magnetoresistive (CMR) properties. Incorporation of an insulating secondary phase into the manganite composites has proven as an effective measure to enhance the low field magnetoresistance (LFMR). This paper reports the structural, microstructural and magnetic properties of (1-x) Pr0.7Sr0.3MnO3 (PSMO): x Al2O3 composites synthesized by the solid-state reaction method. Different compositions of nano-sized Al2O3 (x = 0.00, 0.05, 0.10, 0.15 and 0.20) were appended into the samples to investigate its effect on the physical properties. X-ray diffraction patterns show all samples exhibit polycrystalline PSMO as the major phase and strong orientation along (121) direction throughout the series. The crystal structural parameter is presented by Rietveld refinement. Nano-sized of Al2O3 has distorted the pure PSMO as changes have been observed in bond length and bond angle observed. Surface roughness and particle size show the increment along with increasing Al2O3 composition from the atomic force microscope (AFM) analysis. All samples possess the narrow hysteresis loop with weak ferromagnetic nature. The PSMO: Al2O3 presented in this study is a promising manganite composite which can be utilized in the magnetic sensor applications.

Structure, electrical transport, and magnetoresistance of manganite films on sapphire

In this work, Pr0.7Sr0.3MnO3 (PSMO) films with the thickness of 12 and 36 nm have been grown on (0001) sapphire substrates with six symmetry using pulsed laser deposition technology. The structure, electrical transport, and magnetoresistance (MR) of PSMO films have been investigated. In the PSMO film with the thickness of 12 nm, there is only one metal-to-insulator (MI) transition. Some textures and disorder coexist in the 12-nm-thick PSMO film, reducing temperature dependence of MR. This kind of MR can be explained by the double exchange (DE) theory. We find a low-field MR (LFMR) ~ 38% (at µ0H = 1 T, T = 80 K) and a MR ~ 125% (at µ0H = 5 T, T = 185 K) in this thinner PSMO (12 nm) film. On the contrary, there are two MI transitions in the PSMO film with the thickness of 36 nm. The LFMR ~ 55% (at µ0H = 1 T, T = 115 K) and MR ~ 300% (at µ0H = 5 T, T = 140 K) are obtained in this thicker PSMO (36 nm) film. This kind of MR cannot be explained by the DE theory, which is induced by the charge-ordered antiferromagnetic state. The electrical transport and the MR can be tuned by the charge ordering, multiple textures and the disordering induced by both grain boundary and large lattice mismatch between PSMO film and sapphire. These interesting physical properties in manganite films have opportunities for practical application in developing manganite-based magnetic sensor and memory devices.

Magnetocaloric effect simulation by Landau theory and mean-field approximation in Pr0.5Sr0.5MnO3

The magnetocaloric effect in Pr0.5Sr0.5MnO3 (PSMO) has been successfully modeled in this work. PSMO undergoes a first-order antiferromagnetic charge ordering (AFM/CO) to a ferromagnetic (FM) transition at $ T_{CO}=T_{N}\sim 165$ K followed by a second-order ferromagnetic (FM) to paramagnetic (PM) transition at the Curie temperature, $ T_{C}\sim 255$ K. The magnetocaloric effect in PSMO has been studied by the simulation of the magnetic entropy change $ (-\Delta S_M)$ for these two transitions by developing a numerical approach based on the Landau free energy within the mean-field approximation. Simulated results agree well with the experimental ones for these two transitions.

Impact of synthesis routes on normal and inverse magnetocaloric effects and critical behaviour in the charge-ordered Pr0.5Sr0.5MnO3 manganite

We investigated the effect of both synthesis routes on the physical properties of charge-ordered Pr0.5Sr0.5MnO3 (PSMO) manganites. The samples are prepared by the solid-state reaction (SSR) and the modified sol-gel (SG) method. X-ray diffraction (XRD), SEM and magnetic measurement are used to study the structural, morphological, magnetic, magnetocaloric effect and the critical behaviour of our manganites. XRD studies confirmed the single phase orthorhombic formation of PSMO. Both compounds undergo two successive magnetic phase transitions with the variation of temperature: a paramagnetic (PM)-to-ferromagnetic (FM) transition around $ T_{\rm C}=265$ and 243K followed by an FM-to-antiferromagnetic charge-ordered transition at $ T_{\rm CO}=85$ and 159K for the SG and SSR methods, respectively. Moreover, Banerjee's criteria, Landau analysis and universal curves of phase transitions are also studied to access the magnetic ordering of the PM-FM transition in the samples and confirmed the second-order character. Critical exponents associated with the ferromagnetic phase transition are analyzed and found to be inconsistent with any known universality class. Important magnetic entropy changes and the relative cooling power (RCP) were observed in the sample synthesized through the solid state method as compared to the sol-gel-synthesized sample. The PSMO compounds show both negative ( $ \Delta S_{\rm M}=-1.63813$ J/kgK for SSR and -1.1 for SG) as well as positive ( $ \Delta S_{\rm M}=+5.82$ J/kgK for SSR and +1.52 for SG) magnetocaloric effects under a 2T field at ferromagnetic and charge order transitions, respectively. This feature of successive inverse and normal MCEs in Pr0.5Sr0.5MnO3 are suggested to be applied in some magnetic refrigerators with special designs and functions.

Magnetocaloric effect studying by means of theoretical models in [formula omitted] manganite

In this work, we have used many theoretical models to simulate the magnetocaloric effect (MCE) in the charge ordered Pr0.5Sr0.5MnO3 (PSMO) manganite. This sample undergoes a first order antiferromagnetic charge-ordered (AFM/CO) to a ferromagnetic (FM) transition at TCO∼165 K followed by a second order FM to paramagnetic (PM) transition at Curie temperature, TC∼255 K. The Mean-field theory and the Bean-Rodbell model are called to study deeply the MCE in FM-PM transition. Based on the mean-field theory, we proposed a numerical approach to study the evolution of magnetization versus temperature for the first order AFM/CO – FM transition. By using a phenomenological model, we have compared theoretical and experimental MCE for the above two transitions.

Emergence of ferromagnetism and metallicity in Pr0.5Sr0.5MnO3 nanoparticles

In this paper, we have studied low-temperature magnetic properties and transport dynamics of half-doped Pr0.5Sr0.5MnO3 (PSMO) nano-manganite. Nanoparticles with different average grain sizes are synthesized using chemical pyrophoric reaction route and exhibit same crystal structure. It is reported that particle size reduction in half-doped PSMO manganite interestingly leads to ferromagnetic (FM) metallic behavior which is accompanied by coupled positive magnetoresistance (PMR) (up to 9%) at fields (H ≤ 1kOe at 50K) and negative magnetoresistance (NMR) (∼59% at 100K) at 80kOe fields. Interestingly, maximum PMR is appeared at much lower than the critical field (30kOe) for the melting of insulating -antiferromagnetic (AFM) ordered state. Moreover, it is found that low-temperature AFM-FM phase transition, TN ∼ 135K is smeared out with reduction of particle size; however, the transition is prominent in bulk material. A metastable magnetic state with a mixed fraction of FM and AFM phases is observed below TN. Superparamagnetic (SPM) behavior of PSMO nanoparticles has been revealed by probing ac-susceptibility measurements. Low-temperature transport dynamics has been investigated through four probe resistivity and magneto-transport measurements. A size-induced insulating-metallic phase transition is observed on nano dimension in the range of 125-155K under high magnetic fields; however, the bulk counterpart remains insulating over the entire temperature range. The non-trivial electronic- and magnetotransport properties are explained by the inter-grain spin-polarized hopping mechanism through double exchange (DE) interactions. These issues have been revisited and discussed in the framework of enhanced surface disorder, where surface spins plays the crucial role for inter-grain transport dynamics in nanometric dimension. We believe the present field dependent MR holds excellent potential for future spintronic devices and manifests the exotic properties of strongly correlated materials.

Electrical Transport Properties and Magnetoresistance of Pr<sub>0.67</sub>Sr<sub>0.33</sub>MnO<sub>3</sub>-NiO Composites

A series of polycrystalline bulk samples (Pr0.67Sr0.33MnO3)1-x/ (NiO)x were prepared by solid state reaction, and its structure, electrical transport and magnetoresistance properties were investigated. X-ray analysis showed that parent compound of Pr0.67Sr0.33MnO3 (PSMO) formed in single phase with crystal structure of orthorhombic while secondary phase of NiO can be detected with the addition of composite. The electrical properties showed that the resistivity increased with the addition of NiO due to enhancement of spin dependent-tunneling scattering across the artificial grain boundaries of NiO layer. Magnetic field dependence MR curve at various temperatures clearly indicates that extrinsic magnetoresistance had been enhanced due to addition of NiO as the artificial grain boundary.

Colossal magnetoresistance at wide temperature range in Pr0.7Sr0.3MnO3 film grown on (0001) sapphire

Pr0.7Sr0.3MnO3 (PSMO) films were fabricated on (0001) sapphire substrates by pulsed laser deposition. The structure and transport properties of the films have been investigated. Several textures and disorder coexist in the PSMO films and result in the colossal magnetoresistance (MR) effect at a wide temperature range of 5–210 K. Colossal MR at the wide temperature region provides opportunities for practical application in manganite film devices. Our research results demonstrate that the textures and the disorder state induced by multiple growth orientations can strongly influence the transport properties of film.

The effect of post-annealing on the structure and magnetotransport properties of Pr0.5Sr0.5MnO3 thin film

Pr0.5Sr0.5MnO3 (PSMO) thin film is epitaxially grown on (001)-oriented LaAlO3 single-crystal substrate using pulsed laser deposition (PLD). It is found that the as-grown PSMO film shows compressive strain in plane and tensile strain out of the plane. Upon annealing at 900°C in the air, the strain is significantly relaxed. The paramagnetic to ferromagnetic phase transition temperature TC shifts from 200 K to 220 K, and the antiferromagnetic insulating phase is suppressed in the phase separated state at low temperature. In addition, the magnetoresistance (MR) is found to increase around the ferromagnetic transition temperature, whereas it decreases from 99% to 60% at low temperature of 20 K.

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.

Colossal magnetoresistance of Pr0.7Sr0.3MnO3 layer grown on charge-ordered La0.5Ca0.5MnO3 manganite layer

We present a report of the interfacial reaction between ferromagnetic (FM) Pr0.7Sr0.3MnO3 (PSMO-3) in proximity to charge ordered (CO) La0.5Ca0.5MnO3 (LCMO-5) in a bilayer structure. PSMO-3/LCMO-5 bilayer film with high crystalline quality was epitaxially grown on SrTiO3 (001) substrate by pulsed laser deposition. The bilayer loses 20% of its resistance for only 0.5 T, and loses 50% of its resistance for 2 T. This large low-field magnetoresistance (LFMR) is comparable to some FM/CO multilayers and other mixed compounds including strongly competing phases. LFMR of ∼−73% has been achieved at H = 1 T and T = 185 K. The maximum MR reaches a value of ∼−641% at H = 9 T and T = 205 K and the corresponding MR at room temperature is ∼−30%. The formation of CO anti-ferromagnetic state in LCMO-5 and its collapse (melting) under the applied magnetic field may be responsible for the enhanced MR mentioned above. In other words, the enhancement of MR can be explained by a FM phase percolation. Moreover, exchange bias (EB) cannot be observed in the bilayer at low temperature of 3 K, further confirming the occurrence of FM phase percolation at the PSMO-3/LCMO-5 interface. The disappearance of EB can be explained by a combination of the preferable distribution of FM clusters and FM clusters percolation at the PSMO-3/LCMO-5 interface. Large MR can be realized by using a CO material as a sublayer, which can provide potential application in the used devices.

Surface morphology and magnetic properties in Pr0.7Sr0.3MnO3 layer grown on charge-ordered La0.5Ca0.5MnO3 layer

We report magnetic behaviors in Pr0.7Sr0.3MnO3 (PSMO) layer grown on charge-ordered La0.5Ca0.5MnO3 (LCMO) layer. PSMO/LCMO bilayer film was prepared by pulsed laser deposition on SrTiO3 (001) substrate. Large particulates at the surface of PSMO layer impart inhomogeneous composition in film, resulting in the variation of film's crystalline structure. We find an exchange bias (EB) in the bilayer film with relative roughness and inhomogeneous surface, whereas smooth and homogeneous surface does not lead to an EB effect. It is believed that an antiferromagnetic structure is formed in the inhomogeneous PSMO layer, which causes the EB effect in this system. The present results are discussed and possible explanations are provided based on the random-field model of EB and the related research results.

Exchange-bias field induced by surface inhomogeneities in ferromagnetic/charge-ordered bilayer structure

Epitaxial bilayer structure consisting of ferromagnetic metallic Pr0.7Sr0.3MnO3 (PSMO) and charge-ordered insulator La0.5Ca0.5MnO3 (LCMO) was fabricated on (001) SrTiO3 substrate by pulsed laser deposition. High-resolution synchrotron X-ray diffraction showed high quality of epitaxial layer. However, besides diffraction peaks from PSMO layer, LCMO layer and SrTiO3 substrate, we observed an additional shoulder peak, which might stem from the inhomogeneities of composition in PSMO/LCMO. Further the atomic force microscopy measurement showed the presence of non-stoichiometric large particulates at surface, imparting an overall inhomogeneous composition to the film. This implied that the variation of crystalline structure of PSMO/LCMO occurred due to inhomogeneous composition. Moreover, studies on magnetic properties showed that surface inhomogeneities and ferromagnetic clusters at the PSMO/LCMO interface probably influenced the ferromagnetism of the bilayer film together, tuning exchange bias effect.

Electronic and magneto transport property of Pr0.7Sr0.3MnO3 system in nanometric gran size modulation

Grain size effect on electronic- and magnto-transport properties of hole doped manganite Pr0.7Sr0.3MnO3 (PSMO) in nanometric dimension has been thoroughly investigated under external magnetic field range from zero to ± 8 Tesla down to 4 K. Metal-insulator transition temperature (Tp) which is observed for all the PSMO nanometric samples, differs from the ferromagnetic to paramagnetic transition temperature (Tc) in the nanometric regime compare to its reported bulk counterpart mainly due to the enhanced surface disorder effect. Temperature dependent low field complex magneto- impedance (LFMI) behaviour has also been studied in presence of external magnetic field range of 0 – 800 Oe down to 77 K.

Characterization on surface and interface structure of epitaxial Pr0.7Sr0.3MnO3/La0.5Ca0.5MnO3/Pr0.7Sr0.3MnO3 trilayer

Epitaxial trilayers consisting of ferromagnetic (FM) metallic Pr0.7Sr0.3MnO3 (PSMO) and antiferromagnetic (AFM) insulators La0.5Ca0.5MnO3 (LCMO) were fabricated on (001)-oriented single crystal MgO substrates using pulsed laser deposition technique. High resolution X-ray diffraction (HRXRD), grazing incidence X-ray reflectivity (GIXRR) and atomic force microscope were applied to characterize the surface and interface structure of PSMO/LCMO/PSMO trilayers. The HRXRD patterns of all trilayers implied high quality of epitaxial layer. A structural model including seven layers was presented to theoretically simulate GIXRR data. The perfect GIXRR data fitting of the trilayers indicated that the thickness of the top sublayer at air/PSMO interface was about 2.5nm for all the samples and the mass density of the top sublayer was about 77.66% of PSMO layer. In all trilayers, there existed two disordered layers with thickness of about 4nm resulting from interdiffusion at the PSMO/LCMO interfaces. The root-mean-square (rms) roughness of the surface and interface in the trilayers varied with respect to the thickness of LCMO layer. The surface roughness was consistent with observation from atomic force microscopy. A further analysis indicated that the rms roughness was related to the mismatch strain relaxation in film. Moreover, studies on magnetic properties of PSMO/LCMO/PSMO trilayers show that ferromagnetic clusters at the interface, large roughness at the surface and interface and interdiffusion between PSMO and LCMO layer probably lead to the disappearance of exchange bias.