Critical behavior of La0.7Ca0.3Mn1 x NixO3manganites exhibiting the crossover offirst- and second-order phase transitions

• المؤلف الرئيسي: Phung, ThanhPQ
• التنسيق: مقال
• اللغة: English
• منشور في: Elsevier 2016
• الموضوعات: Magnetic entropy change
• الوصول للمادة أونلاين: http://repository.vnu.edu.vn/handle/VNU_123/10146

We used Banerjee0 s criteria, modified Arrott plots, and the scaling hypothesis to analyze magneticfield dependences of magnetization near the ferromagnetic–paramagnetic (FM–PM) phasetransition temperature (TC) of perovskite-type manganites La0.7Ca0.3Mn1 x NixO3(x¼0.09, 0.12 and 0.15). In the FM region, experimental results for the critical exponentβ(¼0.171 and 0.262 for x¼0.09 and 0.12, respectively) reveal twofirst samples exhibiting tricriticality associated with the crossover offirst- and second-order phase transitions. Increasing Ni-doping content leads to the shift of theβvalue (¼0.320 forx¼0.15) towards that expected for the 3D Ising model (β¼0.325). This is due to the fact that the substitution of Ni ions into the Mn site changes structural parameters and dilutes the FM phase, which act asfluctuations and influence the FM-interaction strength of double-exchange Mn 3þ –Mn4þ pairs, and the phase-transition type. For the critical exponentγ (¼0.976–0.990), the stability in its value demonstrates the PM behavior aboveTCof the samples. Particularly, aroundTC of La0.7Ca0.3Mn1 x NixO3 compounds, magnetic-field dependences of the maximum magnetic-entropy change can be described by a power law of|ΔSmax|pH n , where values n¼0.55–0.77 are quite far from those (n¼0.33–0.48) calculated from the theoretical relationn¼1þ (β 1)/(βþγ). This difference is related to the use of the mean-field theory for the samples exhibiting the magnetic inhomogeneity