Effect In Pr0 Research Articles

Theoretical description of the magnetocaloric effect in Pr0.67Sr0.33MnO3 manganite using the mean-field theory

Theoretical description of the magnetocaloric effect in Pr0.67Sr0.33MnO3 manganite using the mean-field theory

Giant magnetothermal anomalies and direct measurements of the magnetocaloric effect in Pr0.7Sr0.3−xBaxMnO3 manganites

The paper presents the results of a study of magnetization, specific heat (CP), thermal diffusivity (η), thermal conductivity (κ) and direct measurements magnetocaloric effect of polycrystalline samples Pr0.7Sr0.3−xBaxMnO3 (x = 0–0.3). An increase in the Ba concentration leads to a decrease in the Curie temperature (TC), an increase in the disorder parameter (σ2) and a noticeable increase in thermal conductivity of the ferromagnetic phase (FM). The κ(Т) data near ТС revealed small minima and a sharp jump-like change in thermal conductivity upon transition to the FM phase. These results suggest that the anomalies in the temperature dependences of η(Т) and κ(Т) are associated with the scattering of thermal phonons both from distortions of the crystal lattice and from spin fluctuations. The giant change of η (Δη/η ∼ 67%) and κ (Δκ/κ ∼ 33%) was found in a magnetic field of 1.8 T for the x = 0 (Pr0.7Sr0.3MnO3) sample. The maximum values of ∆T, ∆S and relative cooling power (RCP), observed for this sample in a field of 1.8 T, are equal to 1.81 K, 3.38 J/kg K and 74.02 J/kg, respectively. In the studied Pr0.7Sr0.3−xBaxMnO3 samples, the specific cooling power value at f = 0.2 Hz is 0.35, 0.29, 0.21, and 0.11 W/g for x = 0, 0.1, 0.2, and 0.3 sample, respectively.

Magnetic properties and evolution of magnetoresistance effect in Pr0.75Na0.05K0.20Mn1–xFexO3 with $$0\le x\le$$ 0.04

Magnetic properties and evolution of magnetoresistance effect in Pr0.75Na0.05K0.20Mn1–xFexO3 with $$0\le x\le$$ 0.04

The transport properties and large magnetoresistance effect in Pr0.7Sr0.3MnO3 film on SrTiO3

The transport properties and large magnetoresistance effect in Pr0.7Sr0.3MnO3 film on SrTiO3

Anomalous Nernst effect in Pr0.5Sr0.5CoO3

We report the anomalous Nernst effect (ANE) in polycrystalline metallic perovskite Pr0.5Sr0.5CoO3. The transverse Seebeck coefficient (Sxy) was measured at selected temperatures for magnetic fields up to H = 50 kOe and also as a function of temperature at two selected magnetic fields (H = 2 and 10 kOe). While Sxy increases linearly with H above the Curie temperature (TC ∼ 229 K), it changes non-linearly at low fields in the ferromagnetic state and exhibits hysteresis similar to magnetization. Linear extrapolation of the high field Sxy vs H graph to zero field gives Sxy = 0.46 µV/K at 175 K. It is found that the manganite counterpart Pr0.5Sr0.5MnO3 having a similar hole content exhibits much smaller Sxy than Pr0.5Sr0.5CoO3 in a field of 2 kOe. Our analysis suggests that the ANE in this sample is most likely due to asymmetric skew scattering of charge carriers.

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.

Specific heat and magnetocaloric effect in Pr0.6Sr0.4−xAgxMnO3 manganites

The detailed investigation on the specific heat in manganites of Pr0.6Sr0.4−xAgxMnO3 (x = 0.05 and x = 0.1) has been reported. The experimental conditions were: the temperature range 1.8–330 K and applied magnetic fields of 0, 1, 2 and 3 T. Specific heat results confirmed two phase transitions, a structural one at Tstr = 43 K for both samples and a paramagnetic–ferromagnetic one near TPM–FM = 288 K and 284 K for the x = 0.05 and x = 0.1 sample, respectively. For the more doped sample the magnetic field causes the shift of the PM–FM transition temperature towards higher temperatures. A thorough analysis of particular contributions to the specific heat was presented. The indirect magnetocaloric effect was deduced for the more doped sample (x = 0.1). Under an applied magnetic field of 3 T magnetic entropy changes and adiabatic temperature exhibits a maximum. The absolute ΔSmax reaches the value of 1.74 J/mol K, resulting in adiabatic cooling of ΔTad = 0.95 K. Such result confirms presented samples as promising candidates for the magnetic cooling technology at room temperature.

Study of magnetic and electrical properties of Pr0.65Ca0.25Ba0.1MnO3manganite

The magnetic properties and magnetocaloric effect (MCE) in Pr0.65Ca0.25Ba0.1MnO3 have been investigated supplemented by electrical data. X-ray diffraction shows that the sample crystallizes in the distorted orthorhombic system with the Pnma space group. Pr0.65Ca0.25Ba0.1MnO3 undergoes paramagnetic–ferromagnetic (PM–FM) phase transition at TC ∼ 85 K. For a magnetic field change of 5 T, the maximum value of the magnetic entropy change (−ΔSmaxM) is estimated to be 4.4 J kg−1 K−1 around TC with a large relative cooling power (RCP) value of 263.5 J kg−1. While the modified Arrott plots suggested that the magnetic transition belongs to the second order phase transitions, the universal curves of the rescaled magnetic entropy (ΔSM) proved the opposite. The electrical properties of Pr0.65Ca0.25Ba0.1MnO3 have been investigated using impedance spectroscopy techniques. The dc-resistivity (σdc) study shows the presence of semiconductor behavior. Ac-conductivity (σac) analysis shows that the conductivity is governed by a hopping process. From the analysis of the alternating regime, the exponent s variation obtained is in good agreement with Mott theory. The impedance spectrum analysis reveals the presence of a relaxation phenomenon. Based on these analyzes, the sample can be modeled by an electrical equivalent circuit.

Impact of Fe Substitution on Magnetic and Magnetocaloric Effect in Pr0.6Sr0.4Mn1−xFexO3 Manganites

Impact of Fe Substitution on Magnetic and Magnetocaloric Effect in Pr_0.6Sr_0.4Mn_1−<i>x</i>Fe_<i>x</i>O₃ Manganites

Heat capacity and the magnetocaloric effect in Pr0.6Sr0.4Mn1–x Fe x O3 manganite

The heat capacity and the magnetocaloric effect of Pr0.6Sr0.4Mn1–xFexO3(x = 0 and 0.1) manganite have been studied in the temperature range 80–350 K and magnetic fields to 18 kOe. The magnetocaloric effect is estimated using two independent methods: the method of magnetic field modulation (direct method) and from the data on the heat capacity in magnetic field and without magnetic field (indirect method). The substitution of Fe atoms for Mn atoms (x = 0.1) shifts T C by 167 K to lower temperatures; in this case, the magnetocaloric effect (MCE) is changed insignificantly in magnetic field 18 kOe with ΔS M = 2.05 and 2.31 J/kg K for x = 0 and 0.10, respectively.

Electrical conductivity analysis and magnetic properties of Pr0.7Ca0.3Mn0.95Co0.05O3 oxide

The structural, electrical, magnetic and magnetocaloric properties of Pr0.7Ca0.3Mn0.95Co0.05O3 have been studied. The X-ray diffraction refinement results indicate that the sample is single phase and crystallizes in the distorted orthorhombic system with Pnma space group. The investigation of the temperature and frequency dependence of conductance indicates that the sample exhibits a semi-insulator character and the conduction mechanism is explained using hopping model. Complex impedance analysis confirms the contribution of grain boundary in the transport properties in the Pr0.7Ca0.3Mn0.95Co0.05O3 system. Magnetocaloric effect and transition order are investigated by using magnetization measurements. The field dependence of magnetic entropy change and relative cooling power are analyzed and showing the power law dependence. The Landau theory for phase transitions framework is applied to describe the magnetocaloric effect in Pr0.7Ca0.3Mn0.95Co0.05O3 manganite. The obtained results are discussed in terms of magnetoelastic and electron interaction contribution to the magnetic entropy.

Phase separation and magnetocaloric effect in Pr0.5−xGdx Sr0.5MnO3 system

The magnetic properties and the magnetocaloric effect have been studied in Pr0.5−xGdxSr0.5MnO3 (x = 0, 0.05 and 0.1) manganites prepared by the solid state reaction method. Magnetic measurements versus temperature in an applied magnetic field of 0.05 T show that the all samples exhibit a paramagnetic to ferromagnetic transition when temperature decreases. The x = 0.1 sample shows a clear transition, from the ferromagnetic state to the antiferromagnetic one at TN = 125 K. The Curie temperature decreases gradually with increasing gadolinium content. The absolute values of the maximum of magnetic entropy change |ΔSM| for an applied magnetic field of 2 T are equal to1.26, 1.25 and 1.02 J kg−1 K−1 for x = 0, 0.05 and 0.1, respectively. The decrease of |ΔSM| with Gd doping can be attributed to the enhancement of phase separation phenomenon. The magnetic entropy curves follow the universal law corresponding to the second-ordered paramagnetic-ferromagnetic transition.

Effect of Fe substitution on charge order state and magnetocaloric effect in Pr0.5Sr0.5Mn1−xFexO3 (0.00 ≤ x ≤ 0.08) manganites

The charge order state and magnetocaloric effect have been studied in Pr0.5Sr0.5Mn1−xFexO3 (0.00 ≤ x ≤ 0.08) prepared by conventional solid-state reaction. Charge order state is weak in parent Pr0.5Sr0.5MnO3 and absent with increasing doping level. The long range charge order antiferromagnetic state (CO/AFM) reemerges for x = 0.06 and subsequently weak accompanied with rapid collapse in double exchange ferromagnetic order for x = 0.08. Magnetic measurements indicate that Fe does not participate in the double exchange interaction, the Curie temperature (TC) is systematically depressed with increasing Fe content from 265 K (x = 0.00) down to 185 K (x = 0.06). Negative magnetic entropy change (ΔSMmax) of −0.96 J/kg K and large positive value of 2.57 J/kg K in Pr0.5Sr0.5Mn0.94Fe0.06O3 are achieved when it undergoes paramagnetic to ferromagnetic (PM-FM) and ferromagnetic to antiferromagnetic (FM-AFM) magnetic phase transition in a magnetic change of 15.0 kOe. Though the materials with considerable magnetic hysteresis in FM-CO/AFM because of first order magnetic phase transition, it gives a strategy to obtain change order state in manganites.

Critical magnetic behavior and large magnetocaloric effect in Pr0.67Ba0.33MnO3 perovskite manganite

We report results of critical magnetic behavior and magnetocaloric investigations of the perovskite manganite Pr0.67Ba0.33MnO3. The compound exhibits a paramagnetic (PM) to ferromagnetic (FM) transition at the Curie temperature TC, and significant negative magnetoresistance in a wide temperature range. To probe the magnetic interactions responsible for the magnetic transitions, we performed a critical exponent analysis in the vicinity of the FM–PM transition region. Magnetic entropy change ΔSM was estimated from isothermal magnetization data. We have found a remarkable large value of |ΔSM| around TC’s, of about 5.50J/kgK for μ0ΔH=4T and a large relative cooling power (~225J/kg). The analysis was done by using the modified Arrot plot (MAP) method. The values of the obtained critical exponents associated with this transition, β=0.366, γ=1.375 and δ=4.743 are close to those expected for the short range 3D Heisenberg model. The model was also confirmed by using |ΔSM|∝(μ0H)n, the field dependence of magnetic entropy change method. The large measured magnetocaloric effect is presumed to arise as a consequence of the sample preparation route.

Critical behavior and the universal curve for magnetocaloric effect in Pr0.6Ca0.1Sr0.3Mn1−xFexO3 (x = 0, 0.05 and 0.075) manganites

We have investigated the critical behavior of the ferromagnetic Pr0.6Ca0.1Sr0.3Mn1−xFexO3 (x=0, 0.05 and 0.075) compounds by the data of magnetization measurements. To investigate the nature of the magnetic phase transition, a detailed critical exponent study has been performed. The critical exponents β, γ, and δ determined using the modified Arrott plot (MAP), the Kouvel–Fisher method (KF), as well as the critical isotherm (CI) analysis. With these critical exponents, the experimental M (T, H) relations below and above Curie temperature collapse into two universal branches, fulfilling the single scaling equation m=f±(h), where m and h are renormalized magnetization and field respectively. The estimated critical exponents β (0.361⩽β⩽0.380), γ (1.254⩽γ⩽1.342) and δ (4.30⩽δ⩽4.71) are close to those expected for three-dimensional Heisenberg. Interestingly, for the doped samples the values of γ decreased and approached the 3D-Ising (γ=1.24). This reflects an existence of ferromagnetic short-range order in our samples. The substitution of Mn by Fe greatly weakens the influence of double exchange (DE) interactions and promotes the antiferromagnetic interactions (AFM). Moreover, the temperature dependence of the exponent n for a different magnetic field is also studied. The values of n obey to the Curie Weiss law above the transition temperature. In particular, n can be related to the critical exponents β, γ and δ at the magnetic transition from the relation n(TC)=β-1β+γ+1=1+1δ1-1β, where n=0.624, 0.617 and 0.620. These results confirmed the invalidity of mean field theory. Moreover, rescaled entropy data for all compositions collapses into the same universal curve, revealing universal behavior for the magnetocaloric effect in this series of compounds.

Tuning of magnetocaloric effect in Pr0.5Sr0.5MnO3 with minimal Cr substitution

We have investigated the magnetocaloric effect in Pr0.5Sr0.5Mn1−xCrxO3 nanoparticles with x=0, 0.02, and 0.035. Average grain sizes of the nanoparticles are found to be ≃80nm. Magnitude of magnetocaloric effect (MCE) increases for x=0.02 and then decreases for x=0.035. A bulk compound with x=0.02 with average grain size ≃0.5μm has also been investigated and we note that size effect significantly tunes the MCE for this material, in which interplay between ferromagnetic and antiferromagnetic interactions leads to the observed results.

Exchange-bias-like effect in Pr0.75Tb0.25Al2 and Pr0.7Tb0.3Al2 samples

The magnetic behavior of pseudobinary Pr0.7Tb0.3Al2 and Pr0.75Tb0.25Al2 compounds was studied, and a predominant ferrimagnetic ordering was observed. Noteworthy characteristics such as negative magnetization, compensation points and exchange-bias-like (EB-like) effect were found. This EB-like effect was observed at temperatures below the compensation points. The effect is somewhat different from the one already studied in similar systems combining light and heavy rare earths. The results indicate that the EB-like effect characteristics are related to the conduction electron magnetic polarization and an induced unidirectional anisotropy present in these compounds.

Coaction and competition between the ferroelectric field effect and the strain effect in Pr0.5Ca0.5MnO3 film/0.67Pb(Mg1/3Nb2/3)O3-0.33PbTiO3 crystal heterostructures

The coaction and competition between the ferroelectric field effect and the strain effect in Pr0.5Ca0.5MnO3 (PCMO) film/0.67Pb(Mg1/3Nb2/3)O3-0.33PbTiO3 crystal heterostructures were studied. Based on different types of resistance-electric field hysteresis loops at various temperatures, it is clearly identified that the strain effect dominates over the ferroelectric field effect for temperature T above the charge-ordering temperature TCO of PCMO. With the strong localization of charge carriers for T &amp;lt; TCO, the ferroelectric field effect strongly competes with the strain effect and finally dominates over the latter for T &amp;lt; 0.8TCO. Moreover, the poling-induced strain effect is considerably enhanced by a magnetic field, demonstrating the important role of the phase separation in understanding the strain effect in such heterostructures.

Magnetic proximity effect in Pr0.5Ca0.5MnO3/La0.7Sr0.3MnO3 bilayered films

Magnetotransport properties of the Pr0.5Ca0.5MnO3/La0.7Sr0.3MnO3 bilayer and the Pr0.5Ca0.5MnO3and La0.7Sr0.3MnO3 films deposited on LaAlO3 (001) substrate by pulse laser deposition were investigated. X-ray diffraction and high-resolution electron-microscopy analysis reveal that lattice parameters for the constituent sublayers in the bilayer are very close to those for the individual films. It was found that a ferromagnetic transition in the La0.7Sr0.3MnO3 sublayer significantly modifies magnetotransport properties of the Pr0.5Ca0.5MnO3 constituent sublayer due to the magnetic proximity effect. Evidence of this effect includes the appearance of exchange bias interaction between the constituent sublayers, a localized-to-itinerant crossover in the system of polarized electrons, which results in formation of the Griffiths-like ferromagnetic state, and an unusual polar transport of carriers. Experimental results were analyzed within the framework of the modern theoretical approach.

Electric-field control of phase separation and memory effect in Pr0.6Ca0.4MnO3/Pb(Mg1/3Nb2/3)0.7Ti0.3O3 heterostructures

Heterostructures were fabricated by growing Pr0.6Ca0.4MnO3 (PCMO) films on Pb(Mg1/3Nb2/3)0.7Ti0.3O3 substrates. It was shown that the magnetizations of the samples can be tuned dramatically by electric fields via piezostrain and the effect is dominated by the change in phase separation. More interestingly, the electric-field control of magnetization is nonvolatile, manifesting a memory effect of strain. The results were discussed by considering the effect of electric-field-induced strain on the energy landscape of PCMO and the resultant change in phase separation. This work is helpful for exploring the evolution of phase separation with well-controlled strains and the magnetoelectric coupling effect.