Abstract
In this paper we compare the magnetic and electron paramagnetic resonance (EPR) properties of Pr0.5Ca0.5MnO3 (PCMO) and Bi0.5Ca0.5MnO3 (BCMO) charge ordered manganites. PCMO and BCMO samples were prepared by solid state reaction method. A commercial SQUID magnetometer was used to study the dc-magnetization in the temperature range of 10-300 K. The EPR experiments were carried out using a commercial X-band (frequency ∼ 9.4 GHz) spectrometer in the temperature range 4 K – 300 K. Marked differences are found when the magnetic and EPR properties of rare earth (PCMO) and bismuth based manganites (BCMO) are compared. The temperature dependent resonance fields of PCMO and BCMO samples are seen to be opposite to each other. PCMO shows the resonance field behavior similar to other charge ordered manganites, i.e., decreases with the decrease in temperature whereas the resonance field of BCMO increases with a decrease in temperature. The opposite behavior of resonance field could be due to the different magnetic structures present in the BCMO manganite.
Highlights
Charge ordering is one of the interesting properties shown by managanites of general formula R1-x Ax MnO3 (R = rare earth cation such as La3+, Pr3+, Nd3+ Bi3+ etc and A = alkaline earth cation such as Ca2+, Sr.2+, Ba2+ etc)
From X-ray diffraction studies of PCMO is found to crystallize in the orthorhombic structure where as BCMO sample is found to crystallize in the monoclinic structure
Two transitions can be observed in the magnetization curve of Pr0.5Ca0.5MnO3, the first has been found at 245K and the second transition is observed at 170 K which corresponds to charge order temperature TCO and Néel temperature TN respectively while in Bi0.5Ca0.5MnO3 sample TN was found at 135 K
Summary
When the lone pair character is dominant, Bi3+ ion has the same as that of rare earth manganites (⟨rBi⟩ ∼1.24 Ao). The p-type atomic orbital of bismuth may be the origin for the differences in transport properties of BiMnO3 and rare-earth compounds. The neighboring zigzags are AF coupled; the ordering in the c direction is AF This model with two different Mn sites is called site centered model (CE type). The alternative model of CO/OO is the bond-centered model (CE′ type) which involves the trapping of an electron at some of the Mn-O-Mn bridges It leads to the formation of the Zener polaron state in the ab plane.. In this paper we compare the results of magnetization and electron paramagnetic resosnce (EPR) properties of Pr0.5Ca0.5MnO3 (PCMO) and Bi0.5Ca0.5MnO3 (BCMO) manganites to understand the different nature of the bismuth based manganites
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