Polycrystalline La0 Research Articles

Application of spark plasma sintering to the manufacture of La2-xSrxCuO4 superconducting ceramics

To explore the possibility of improving the critical current density (Jc) of polycrystalline La1.84Sr0.16CuO4 (LSCO) superconductor ceramics, high density La1.84Sr0.16CuO4 samples have been prepared by means of spark plasma sintering (SPS). Structural and superconducting properties of samples made by different variations of the process have been measured for systematic comparison. The density of the SPS samples can reach up to 98 % of the theoretical density of LSCO, but the critical temperature (Tc) and critical current density (Jc) are suppressed by the process. Subsequent annealing has been applied to improve the properties of the SPS samples. After treatment at 1050 °C, in spite of partial decomposition that was observed on the surface of the samples, the Jc of LSCO was significantly improved. Detailed data as well as assumptions for explaining these results are provided. The SPS technique, coupled with a suitable post-annealing treatment is thereby appearing as a possible methodology to improve the critical current density of polycrystalline high temperature cuprate superconductors.

Densification, phase composition, microstructure and properties of spark plasma sintered La0.6Ce0.3Pr0.1B6 bulks

This paper studied the densification, phase composition, microstructure and properties of polycrystalline La0.6Ce0.3Pr0.1B6 bulks prepared by SPS. The dense specimen (98.9 % in relative density) with the average grain size of 15.46 μm has been determined to be a CsCl-type single-phase substitutional solid solution without any impurities or other secondary phases. The homogenous elemental distributions of La, Ce and Pr have been confirmed by both microscale and nanoscale. The room temperature (RT) Vickers hardness (Hv), indentation fracture toughness (KIC) and flexure strength of the dense specimen have been measured to be 23.0 GPa, 2.04 MPa m1/2 and 305.1 MPa, respectively. The Berkovich hardness (HB) and elastic modulus (E) of the dense specimen have been measured to be 30.0 GPa and 376.0 GPa, respectively, by nanoindentation tests at a maximum load of 40 mN. In comparison with the polycrystalline LaB6 bulk, the lower work function Φ of 2.64 eV evaluated by UPS and the larger thermionic emission current densities measured at the same operating condition suggest that the polycrystalline La0.6Ce0.3Pr0.1B6 bulk is a superior-performance thermionic cathode material.

Effect of the glycerol dispersant on the structure, electrical transport and magnetoresistive properties of La0.67Ca0.33MnO3 ceramics prepared by the sol-gel routine

In this paper, the sol-gel technique is employed to synthesize polycrystalline La0.67Ca0.33MnO3 (LCMO) ceramics, where methanol is chosen as the solvent. The crystal structure, morphology, as well as electrical and magnetoresistive properties were examined. Moreover, the effect of amount of the dispersant glycerol on the properties of LCMO ceramics is studied. X-ray diffraction (XRD) results showed that all samples crystallized in single phases with orthogonal perovskite structure (pnma space group), without any detectable impurity phases. Results reveal that the grain size of LCMO ceramics exhibits an initial increase followed by a decrease, accompanied by a similar behavior in the temperature coefficient of resistance (TCR) and magnetoresistance (MR). When the volume ratio of glycerol and methanol reached 2 %, the grain size is determined to be 7.30 μm, with TCR value of 25.02 % K−1 at T= 263.2 K, and MR value recorded at 55.40 %. The study elucidates the influence of glycerol on LCMO polycrystalline ceramics and optimize the fabrication process, thereby improve the electric transport property and magnetoresistance.

Sensing characteristics and EPIR Studies on composite manganites: Role of nanoparticles in the micronsized matrix lattice

In the present communication, the electrical transport properties have been investigated for manganite-based composites consisting of different weight fractions of nanoparticles of LaMnO3 (LMO) and polycrystalline La0.7Ca0.3MnO3 (LCMO). A complex phase separation scenario has been proposed to understand the hysteretic resistive nature exhibited by manganite matrix composites. The role of complex phase separation has been discussed for the manganite composite resistivity and temperature coefficient of resistance (TCR) dependence on temperature, thermal cycle, current and LMO content as well as their sensitivity for voltage and current have also been examined. Observed electric pulse-induced resistance (EPIR) switching in these composites under different applied voltages and magnetic fields have been understood based on a complex phase separation scenario and the formation–rupture of conducting filamentary paths. Tuning of magnetic field-dependent resistance and magnetoresistance (MR) with the influence of different resistance states of LMO–LCMO composites has been understood in depth.

Strain-induced charge ordering above room temperature in rare-earth manganites.

Most known mixed manganites containing rare-earth elements demonstrate a pronounced charge ordering (CO) state below room temperature. The behavior of the magnetic susceptibility and electronic magnetic resonance of polycrystalline Pr1-xSrxMnO3/YSZ (x = 0.2 and x = 0.4) films without a pronounced texture indicates the formation of the CO phase in the samples at temperatures close to and above room temperature. Moreover, this phase manifests itself with a typical sign of martensitic transformation. The same phenomenon has been traced for textured polycrystalline La0.7Sr0.3MnO3/YSZ films. Electron microscope data indicate the presence of internal strain within the films, which is probably responsible for the formation of the CO phase. It is assumed that the reasons for the appearance of such strain include the crystallite size and the boundary between them. The results obtained provide the basis for the development of new research and technological tasks for the generation of the high-temperature CO state in various polycrystalline rare-earth manganites, since this state contributes to the manifestation of interesting magnetocaloric, magnetoelectric and multiferroic properties. In addition, recent data has opened up new opportunities for studying the strain-induced phenomena in such materials.

Influence of heat sintering on the physical properties of bulk La0.67Ca0.33MnO3 perovskite manganite: role of oxygen in tuning the magnetocaloric response.

The effect of heat treatments on bulk poly-crystalline La0.67Ca0.33MnO3 perovskite manganite is presented, to explore the possible enhancement in magnetocaloric performance. Samples were prepared via conventional solid-state reaction route with annealing and sintering at various temperatures. Detailed measurements of temperature-dependent and field-dependent magnetization were carried out to estimate the Curie point and order of magnetic transition. The increased sintering temperature results in a steep transition near the TC, and establishes the magnetic sensitivity as well as the active zone for substantial magnetocaloric performance, at about 168.2% for the LCM9 (sintered at 900 °C) sample. The cause for the significant improvement in the magnetic and magnetocaloric response is brought to light using detailed X-ray photoelectron spectroscopy (XPS) analysis, highlighting the role of oxygen in modifying the Mn3+/Mn4+ charge ratio. The maximum value of the isothermal magnetic entropy change for the optimized sample is found to be 6.4 J kg-1 K-1, achieved at 269 K, while temperature-averaged entropy change (TEC) values, TEC(ΔTH-C = 3 K) and TEC(ΔTH-C = 5 K), of 6 J kg-1 K-1 and 5.2 J kg-1 K-1, respectively, were obtained with a low magnetic field change of 20 kOe. The obtained isothermal entropy change at low field for the optimized La0.67Ca0.33MnO3 sample is higher than that of pure Gd and most oxide-based materials. The relative cooling power (RCP) value is around 93 J kg-1 (ΔH = 20 kOe). The order of the phase transition is examined with universal scaling; the scaled entropy change curves confirm the collapse onto a single curve for LCM9, asserting second-order character, whereas the breakdown of the curve with a dispersion relation (d) of 101.1% at Θ = -5 confirms the onset of intrinsic first-order nature in the case of the high-temperature-sintered samples. Calorimetry measurements show thermal hysteresis of 2.4 K and 7.1 K for LCM11 (sintered at 1100 °C) at ramp rates of 5 K min-1 and 10 K min-1, respectively, confirming the first-order nature of the magnetic transition.

The modifications in structural, optical, and electro-magnetic phase transition of Vanadium-doped La-based manganite ceramics La0.7Pb0.3Mn1−yVyO3 (y = 0 – 0.1)

The present paper is centred around the investigation of the structural, electrical, and magnetic properties displayed by the novel perovskite polycrystalline La0.7Pb0.3Mn1−yVyO3 (y = 0 – 0.1) prepared via the conventional solid-state technique. The structural properties of the samples were assessed through the utilisation of X-ray diffraction (XRD) analysis. Subsequently, the obtained diffraction data underwent refinement employing Rietveld refinement techniques in order to determine the structural parameters of the samples a, b, c, V and Mn–O bond length and angle. The study of X-ray diffraction (XRD) peaks reveals that all the samples exhibited crystallization in a single phase, devoid of any impurities. All of the samples exist in rhombohedral orientation with a space group of R-3c. The tolerance factor of the samples was calculated in order to assess the severity of lattice distortion, decrease from 0.872 (y = 0) to 0.831 (y = 0.1). The microstructural characteristics of the samples were analysed using a field-emission scanning electron microscope (FESEM). The morphology results reveal that a rise in the amount of V leads stimulates the grain growth in the sample, as evidenced by the increase in grain size from 2.17 µm (y = 0) to 3.71 µm (y = 0.1). The Fourier transform infrared (FTIR) analysis revealed an absorption range of 500 – 600 cm-1, which is indicative of the Mn–O bond deformation vibration. This observation suggests the presence of a MnO6 bond in the sample. The Tauc plots derived from the UV-Vis spectroscopy data reveal a notable increase in the optical bandgap (Eopt) as the concentration of V increases. Specifically, the Eopt values rise from 1.71 eV (y = 0) to 2.30 eV (y = 0.1), falling within the range typically observed for semiconductor materials. A distinct metal-insulator transition was observed in all of the samples, exhibiting a range of TMI values ranging from 250 K to 292 K. The scattering model was employed to determine the itinerant eg behaviour in the low temperature region, whilst the SPH model was used to explore the conduction behaviour in the high temperature region. The magnetic characteristic of the samples was investigated using the Alternating Current Susceptibility (ACS) and Vibrating Sample Magnetometer (VSM) techniques, which confirms the existence of a shift in phase from ferromagnetic (FM) to paramagnetic (PM). The TC value exhibits a declining trend from 298.8 K (y = 0) to 274.8 K (y = 0.1).

Temperature Dependence of Complex Relative Permeability of the Polycrystalline La0.7Sr0.3MnO3

<p>吾人量測多晶態鑭鍶錳氧變化溫度的電阻率與頻率範圍為 10 kHz 至 10 MHz 的相對複數磁導率特性。樣品室溫電阻率很小，僅為數 m⋅Ωcm。電阻率隨著溫度增加，在相轉變溫度 TP = 361 K 附近顯現金屬到半導體的相轉變。室溫量測到的磁譜顯現與磁壁位移有關的鬆弛特性，色散情況非常明顯。隨著溫度升高，磁導率增加，在居禮溫度 TC前達到最大值，然後迅速下降。當溫度從室溫增加，磁壁位移鬆弛頻率 fr幾乎保持不變。當溫度升高到 TC附近，由於磁導率迅速降低，fr劇烈增加。在 TC以上，磁譜的色散現象消失。量測到的 fr與理論值相當符合，可看出磁壁位移的阻滯來源主要源自於渦電流阻滯。</p> <p> </p><p>The temperature-dependent resistivity and complex relative permeability of the polycrystalline La0.7Sr0.3MnO3 have been investigated in the frequency range 10 kHz -10 MHz. The measured room-temperature resistivity is of the order of mcm. As the temperature increases, the resistivity increases and shows a metal-insulator transition. The transition temperature TP is about 361 K. There are pronounced dispersions of the relaxation in the measured spectra, which are due to the domain-wall displacement. The magnitude of permeability increases with increasing temperature, reaches its maximum value near the Curie temperature TC, and then abruptly drops. As the temperature increases, the relaxation frequency fr almost remains a constant value. However, it rapidly increases around TC due to the suddenly decrease of the permeability. The dispersion phenomena of the permeability spectra disappear above TC. The consistence of the measured and calculated fr value shows that the damping factor of domain-wall displacement mainly comes from the eddy current.</p> <p> </p>

Microstructure, Magnetic and Electrical Transport Properties of Sol-Gel Synthesized La<sub>0.7</sub>Sr<sub>0.2</sub>Ca<sub>0.1</sub>MnO<sub>3</sub>:TiO<sub>2</sub> Composite

Electrical transport in materials have been studied extensively due to its great potential in spintronic technology. The introduction of the secondary phase into the manganite matrix can modify the electrical properties, subsequently improving the low-field magnetic resistance (LFMR). In this work, we study the change in electrical properties at different temperatures of polycrystalline (1-x)La0.7Sr0.2Ca0.1MnO3/xTiO2 (LT) composites where x = 0, 0.05 and 0.1. Polycrystalline La0.7Sr0.2Ca0.1MnO3 (LSCMO) was synthesized by sol-gel method, calcined at 700 °C, and pre-sintered at 800 °C for 6 h before adding TiO2. TiO2 as filler was mixed with LSCMO by wet mixing and stirring for about 30 min until a homogeneous compound was formed. Composite LT was then inserted to oven up to 100 °C for 2h to remove the moisture, compacted at 10 MPa, and sintered at 1200°C for 12 h. All samples in the LSCMO phase have a rhombohedral crystal structure with space group R3c. The crystal structure parameters were studied using Rietveld refinement through GSAS II software. The sample was characterized by SEM to represent the morphology of the sample. As the TiO2 content increased, the magnetization decreased, as observed by VSM analysis at room temperature. The electrical transport properties of pure LSCMO and LT were characterized by cryogenic from 195K to 260 K. The resistivity of LT10 is too high compared to that of LT5 and as the temperature increases, the resistivity in this range will decrease. For 200 K, the resistivity of LSCMO, LT5 and LT10 are 3.09 x 10-2 ohm.cm, 4.40 x 103 ohm.cm and 4.77 x 104 ohm.cm respectively.

Magnetic and Magnetocaloric Properties of Nano- and Polycrystalline Bulk Manganites La0.7Ba(0.3−x)CaxMnO3 (x ≤ 0.25)

Here we report the synthesis and investigation of bulk and nano-sized La0.7Ba0.3−xCaxMnO3 (x = 0, 0.15, 0.2 and 0.25) compounds that are promising candidates for magnetic refrigeration applications. We compare the structural and magnetic properties of bulk and nano-scale polycrystalline La0.7Ba0.3−xCaxMnO3 for potential use in magnetic cooling systems. Solid-state reactions were implemented for bulk materials, while the sol–gel method was used for nano-sized particles. Structurally and morphologically, the samples were investigated by X-ray diffraction (XRD), optical microscopy and transmission electron microscopy (TEM). Oxygen stoichiometry was investigated by iodometry. Bulk compounds exhibit oxygen deficiency, while nano-sized particles show excess oxygen. Critical magnetic behavior was revealed for all samples using the modified Arrott plot (MAP) method and confirmed by the Kouvel–Fisher (KF) method. The bulk polycrystalline compound behavior was better described by the tricritical field model, while the nanocrystalline samples were governed by the mean-field model. Resistivity in bulk material showed a peak at a temperature Tp1 attributed to grain boundary conditions and at Tp2 associated with a Curie temperature of Tc. Parent polycrystalline sample La0.7Ba0.3MnO3 has Tc at 340 K. Substitution of x = 0.15 of Ca brings Tc to 308 K, and x = 0.2 brings it to 279 K. Nanocrystalline samples exhibit a very wide effective temperature range in the magnetocaloric effect, up to 100 K. Bulk compounds exhibit a high and sharp peak in magnetic entropy change, up to 7 J/kgK at 4 T at Tc for x = 0.25. To compare the magnetocaloric performances of the studied compounds, both relative cooling power (RCP) and temperature-averaged entropy change (TEC) figures of merit were used. RCP is comparable for bulk polycrystalline and nano-sized samples of the same substitution level, while TEC shows a large difference between the two systems. The combination of bulk and nanocrystalline materials can contribute to the effectiveness and improvement of magnetocaloric materials.

Polycrystalline La0.66Gd0.04Ca0.3MnO3 for magnetic-response applications: concurrent anisotropic magnetoresistance and magneto-transport under a low magnetic field

Polycrystalline La0.66Gd0.04Ca0.3MnO3 with a large anisotropic magnetoresistance (−30%) value achieved under a magnetic field of 1 T.

Enhanced electrical transport properties of polycrystalline La0.67Sr Ca0.23-K0.1MnO3 ceramics through A-site multielement co-doping

Current research on perovskite materials is mainly focused on how to achieve a high temperature coefficient of resistivity (TCR) in anticipation of application in infrared detection. In this study, we report the superior electrical transport properties of polycrystalline La0.67SrxCa0.23-xK0.1MnO3 (LSCKMO) (0.03 ≤ x ≤ 0.13) ceramics produced through the sol-gel process using different Sr doping contents. Based on previous studies, polycrystalline manganite ceramics with a higher TCR at room temperature were obtained by optimising the composition ratio of Sr or Ca. In the process of continuous doping, the crystal structure of the polycrystalline LSCKMO ceramics changed significantly from Pnma to R 3‾ c. The final polycrystalline La0.67Sr0.10Ca0.13K0.1MnO3 ceramic material was obtained with a TCR of 17.16% K-1 and peak TCR temperature of 289.42 K, demonstrating that suitable candidates can be obtained for infrared detection technology.

Spark plasma sintering of polycrystalline La0.6Ce0.3Pr0.1B6–ZrB2 composites

AbstractThis paper has studied the densification, microstructure, and properties of polycrystalline La0.6Ce0.3Pr0.1B6–ZrB2 composites prepared by spark plasma sintering (SPS). The highest relative density of 98.7% is obtained at the SPS condition of axial mechanical pressure 50 MPa, sintering temperature 1900°C and holding time 5 min. The Vickers hardness decreases linearly from the maximum value of 21.49 GPa to the value of 8.24 GPa with the tested temperature increased from room temperature to 1000°C. The effects of crack deflection and bridging have resulted in the fracture toughness of 4.56 MPa m1/2 of dense polycrystalline La0.6Ce0.3Pr0.1B6–ZrB2 composite. The J1kV of 7.02 A/cm2 obtained at 1600°C, the work function of 2.743 eV determined by ultraviolet photoelectron spectroscopy, and the good oxidation resistance below 1100°C in air have revealed that the dense polycrystalline La0.6Ce0.3Pr0.1B6–ZrB2 composite has a good potential to be a promising hot cathode material.

Magnetic Properties of La0.81Sr0.19Mn0.9Fe0.1−xZnxO3 (x = 0, x = 0.05)

Magnetic properties of polycrystalline La0.81Sr0.19Mn0.9Fe0.1−xZnxO3 (x = 0, 0.05) have been investigated by means of electron spin resonance, magnetic susceptibility, and Mössbauer measurements. Both samples show a clear ferromagnetic transition. The Curie temperature TC decreases on increasing Fe content (x = 0.05—TC = 222 K; x = 0—TC = 148 K). Mössbauer studies indicate that Fe in these compounds is in the trivalent high-spin state. The temperature evolution of the Mössbauer spectra at low temperatures (T < TC) is typical for ferromagnetic clusters with a wide distribution in size and magnetic correlation length. The inverse susceptibility of all the samples deviates from the Curie–Weiss law above TC, indicating the presence of fluctuations on approaching magnetic order. An anomalous downturn of the inverse susceptibility for x = 0.05 significantly above TC and the concomitant observation of ferromagnetic resonance signals coexisting with the paramagnetic resonance up to approximately room temperature, is caused by a Griffiths-like behavior. This regime is characterized by the coexistence of ferromagnetic entities within the globally paramagnetic phase.

Magnetic properties and critical behavior of the perovskite manganite La0.825Sr0.175MnO3

Polycrystalline La0.825Sr0.175MnO3 was prepared by solid state reaction method. It exhibits a ferromagnetic–paramagnetic phase transition at TC∼286 K. The intrinsic magnetic properties were clarified by the scaling theory and the isothermal magnetization measured around TC. Based on the modified Arrott plot, Kouvel–Fisher method and Widom relation, the critical exponents are determined to be β=0.308(7), γ=1.065(8), δ=4.457(17). Normalization of the critical exponents shows that the extended exchange interaction decays with J∼r−4.861, consistent with Tricritical mean field model. Rhodes–Wohlfarth ratio PC/MS>1 suggests that La0.825Sr0.175MnO3 is completely itinerant ferromagnet.

Structural, electrical, and magnetic transport properties of La0.72Ca0.28Mn1−xCrxO3 (0 ≤ x ≤ 0.06) ceramics

To obtain comprehensive materials with both high temperature coefficient of resistivity (TCR) and magnetoresistance (MR) at low magnetic fields, polycrystalline La0.72Ca0.28Mn1−xCrxO3 (x = 0, 0.02, 0.04, 0.06) ceramics were prepared herein by sol–gel method. Electronic configuration of Cr3+ ions is similar to that of Mn4+ ions, therefore, successive substitution of Mn with Cr increases electrical resistivity and decreases metal–insulator transition temperature of ceramics, even yielding hump-like feature for Cr-rich (x = 0.06) samples. The best TCR (28.50%·K−1) and MR (72.37%) values were obtained simultaneously at Cr dopant content of 0.02 (La0.72Ca0.28Mn0.98Cr0.02O3). Strong response of the material to temperature and magnetic field was caused by minimal symmetry of orthorhombic structure and the most robust Jahn–Teller distortion. With increasing Cr content, Mn3+/Mn4+ or Mn3+/Cr3+ double exchange was diluted, and Cr3+/Cr3+ or Cr3+/Mn4+ superexchange was promoted. However, the internal competition effect was not conducive to the improvement of material properties.

Experimental and theoretical study of magnetic and magnetocaloric properties of the lacunar La0.8□0.2MnO2.8 compound: Bean-Rodbell model

In this paper, our research focuses on the correlation between structural and magnetic properties of the lacunar polycrystalline La0.8□0.2MnO2.8. The structural analysis proves a coexistence between R-3c and Pnma crystallographic structure. The analysis of the hysteresis loop shows that La0.8□0.2MnO2.8 sample is a Ferromagnetic soft material with an antiparallel magnetic coupled for both phases (Pnma and R-3c). Using servals theoretical approaches, the anisotropic parameters were estimated. The magnetocaloric properties were also investigated. A good result of the relative value of cooling power has been achieved (60% of that of Gd at 2 T) indicating that the material is a potential candidate for magnetic refrigeration application. The use of the Bean-Rodbell model based on the mean field theory allowed us to examine the nature of the magnetic transition and to calculate the magnetic and magnetocaloric properties with good accuracy. Moreover, within the framework of the mean-field theory, the spontaneous magnetization values MSp were estimated using the magnetic entropy change curves (-ΔS (M)).

Magnetostriction in microwave synthesized La0.5Ba0.5CoO3

A single phase polycrystalline La0.5Ba0.5CoO3-d sample possessing cubic structure (space group Pm3̄m) was synthesized by microwave irradiation within 20 minutes of processing time and its structural, magnetic, electrical, and magnetostrictive properties were investigated. While the temperature dependence of field-cooled magnetization (M) in a field of H = 0.5 kOe indicates the onset of ferromagnetic transition at TC = 177 K, irreversibility between the zero field-cooled and field cooled M(T) persists even at H = 3 kOe. M(H) at 10 K does not saturate at the maximum available field and has a much smaller value (0.83 μB/Co in a field of 50 kOe) than 1.9 μB/Co expected for spin only contribution from intermediate Co3+ and Co4+ spins. Resistivity shows insulating behavior down to 10 K and only a small magnetoresistance (∼ -2% for H = 70 kOe) occurs around TC. All these results suggest a magnetically heterogeneous ground state with weakly interacting ferromagnetic clusters coexisting with a non-ferromagnetic phase. The length of the sample expands in the direction of the applied magnetic field (positive magnetostriction) and does not show saturation even at 50 kOe. The magnetostriction has a maximum value (λpar = 265 x 10-6) at 10 K and it decreases with increasing temperature. The smaller value of λpar compared to the available data on La0.5Sr0.5CoO3 (λpar = 900 x 10-6) suggests that the non-ferromagnetic matrix is most likely antiferromagnetic and it restrains the field-induced expansion of ferromagnetic clusters in the microwave synthesized La0.5Ba0.5CoO3-d sample.

Local magnetic properties of La0.83Sr0.17Mn0.9Fe[formula omitted]Zn[formula omitted]O3

Magnetic properties of polycrystalline La0.83Sr0.17Mn0.9Fe0.1−xZnxO3 (x=0, x=0.05) have been investigated by means of electron spin resonance, magnetic susceptibility, and Mössbauer measurements. Both samples show a clear ferromagnetic transition. The Curie temperature TC decreases on increasing Fe content. Mössbauer studies indicate that Fe in these compounds is in the trivalent high-spin state. The temperature evolution of the Mössbauer spectra at low temperatures (T<TC) is typical for ferromagnetic clusters with a wide distribution in size and magnetic correlation length. The inverse susceptibility of all the samples deviates from the Curie–Weiss law above TC, indicating the presence of fluctuations on approaching magnetic order. An anomalous downturn of the inverse susceptibility for x=0.05 significantly above TC and the concomitant observation of ferromagnetic resonance signals coexisting with the paramagnetic resonance up to approximately room temperature, is caused by a Griffiths-like behavior. This regime is characterized by the coexistence of ferromagnetic entities within the globally paramagnetic phase.

Influence of polymorphic magnetic phases on exchange bias effect in bulk and nanocrystalline La0.375Ca0.625MnO[formula omitted] compound

Magnetic properties and exchange bias effect of the polycrystalline and nanocrystalline La0.375Ca0.625MnO3 compounds have been presented. With reduction of the particle size, uncompensated surface spin induced ferromagnetism is pronounced in nanocrystalline sample. However, at higher magnetic field value, long range charge ordering (associated with antiferromagnetic nature) is predominant even in nanoparticles similar as bulk counterpart. Exchange bias properties of both compounds have been found at low temperature with increasing nature depending on the cooling magnetic field. Significantly large value of the exchange bias effect in this particular bulk compound and modification of it in nanocrystalline sample is addressed considering the disordered polymorphs developed within the charge-orbital ordered phase.