Role of structural, morphological, and electronic characteristics in investigating the low temperature transport and magnetic behavior of Sr doped Sm2NiMnO6

Abstract

Oxide double perovskites of the form R2NiMnO6 (R= rare-earth) are known to possess the multifunctional behavior. Herein, we have induced structural and electronic modifications in Sm2NiMnO6 system by Sr doping to form Sm2−xSrxNiMnO6 (x = 0.0, 0.2, and 0.4) and accordingly investigated the structural, morphological, electronic, dielectric, magnetic and magnetoresistance properties. Sm2NiMnO6 has monoclinic structure with P21/n space group and doping with Sr does not change the phase of compound. Microstructure studies suggest a decrease in the grain size with increase in Sr doping while elemental overlay and analysis suggest the presence of known elements in uniformity. Chemical valency indicates the existence of mixed valence of Ni and Mn cations along with presence of oxygen vacancies in all the sample of Sm2−xSrxNiMnO6 (x = 0.0, 0.2, and 0.4). Frequency (200 Hz to 2 MHz) and low temperature (100–320 K) dependence of dielectric measurements have been carried out to observe the behavior of dielectric constant and dielectric loss. With increase in concentration of Sr, the dielectric constant decreases while the dielectric loss increases. Temperature variation of ac conductivity as well as resistivity suggests the negative temperature coefficient of resistance, depicting the semiconducting behavior of all the samples. Temperature variation of magnetization in terms of field cooled (FC) and zero field cooled (ZFC) curves shows the presence of two magnetic transitions in all the three samples. One pertains to paramagnetic to ferromagnetic transition temperature and another is due to downturn in magnetization at lower temperature. Sr doping also causes an increase in the magnetic ordering temperature. Field variation of magnetization shows the ferromagnetic nature of all the three samples, where the saturation magnetization decreases with increase in temperature as well as increase in Sr concentration. Temperature dependence of resistivity at different magnetic fields indicates the presence of magnetoresistance effect in all the three samples. These studies highlight the role of Sr doping in determining and influencing the various physical properties discussed in this paper and the importance of these double perovskite systems for future material design and various technological applications.