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تسجيل مستخدم جديدLow temperature irreversibility induced by thermal cycles on two prototypical phase separated manganites
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We have studied the effect of irreversibility induced by repeated thermal cycles on the electric transport and magnetization of polycrystalline samples of La0.5Ca0.5MnO3 and La0.325Pr0.3Ca0.375MnO3. An increase of the resistivity and a decrease of the magnetization at different temperature ranges after cycling is obtained in the temperature range between 300 K and 30 K. Both compounds are known to exhibit intrinsic submicrometric coexistence of phases and undergo a sequence of phase transitions related to structural changes. Changes induced by thermal cycling can be partially inhibited by applying magnetic field and hydrostatic pressure. Our results suggest that the growth and coexistence of phases with different structures gives rise to microstructural tracks and strain accommodation, producing the observed irreversibility. Irrespective of the actual ground state of each compound, the effect of thermal cycling is towards an increase of the amount of the insulating phase in both compounds.
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We have studied the irreversibility of the magnetization induced by thermal cycles in La0.5Ca0.5MnO3 manganites, which present a low temperature state characterized by the coexistence of phases. The effect is evidenced by a decrease of the magnetizat
ion after cycling the sample between 300 and 50 K. We developed a phenomenological model that allows us to correlate the value of the magnetization with the number of cycles performed. The experimental results show excellent agreement with our model, suggesting that this material could be used for the development of a device to monitor thermal changes. The effect of thermal cycling is towards an increase of the amount of the non ferromagnetic phase in the compounds and it might be directly related with the strain at the contact surface among the coexisting phases.
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We have investigated the change in entropy with direct measurements of heat flow as a function of magnetic field at fixed temperatures across the entire phase diagram of the phase-separated (PS) compound La$_{0.25}$Pr$_{0.375}$Ca$_{0.375}$MnO$_3$ (LP
CMO). At this composition, the compound shows competing charge-ordered/antiferromagnetic (CO/AF) ground states. At a fixed temperature, we observe an increase in hysteresis in the entropy as a function of the applied field. The heat flux shows progressively irreversible hysteresis, which characterizes the energy barriers between the two competing ground states, as the temperature is lowered. The increase in the heat loss correlates with the increase in magnetic viscosity in the phase-separated state. Keywords: manganites, avalanche effect, phase transition, heat flow, DSC, entropy. Corresponding author: [email protected] . On 10 April 2020, this JAC-Elsevier article was accepted. Yet, its online publication shows numerous errors: Cut-off text, missing Figure Captions, incomplete Table ... None of which is our fault! This makes our paper hard to read, study and/or understand. This reproduction is our final (error-free!) revision. When citing our refereed paper, please also refer to this arXiv print. Thank you for understanding
In this work we address the interplay between two phenomena which are signatures of the out-of-equilibrium state in phase separated manganites: irreversibility against thermal cycling and aging/rejuvenation process. The sample investigated is La0.5Ca
0.5MnO3, a prototypical manganite exhibiting phase separation. Two regimes for isothermal relaxation were observed according to the temperature range: for T > 100 K, aging/rejuvenation effects are observed, while for T < 100 K an irreversible aging was found. Our results show that thermal cycles act as a tool to unveil the dynamical behavior of the phase separated state in manganites, revealing the close interplay between static and dynamic properties of phase separated manganites.
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