Magnetic phase transitions in praseodymium-barium doped manganites
The doped manganese oxide Pr0.70Ba0.30MnO 3+δ shows distinct magnetic phase transitions before and after reoxidation. The parent sample as-prepared is oxygen stoichiometric A-site ionic disordered Pr0.70Ba0.30MnO 3 (where Pr and Ba atoms are randomly distributed on the A-sites and δ=0). After a two-step reduction-reoxidation procedure, we obtain a reoxidized sample that is oxygen non-stoichiometric A-site ionic ordered Pr0.70Ba0.30MnO3.05 (δ=0.025). The reoxidized sample is actually phase separated in two distinct layers: (i) an oxygen stoichiometric A-site ordered PrBaMn2 O6 phase and (ii) an oxygen non-stoichiometric A -site disordered Pr0.90Ba0.30MnO3.05 (δ=0.05) phase. These two chemical phases are exchange-coupled and correspond to two magnetic phases. ^ The parent sample Pr0.70Ba0.30MnO3 undergoes a conventional Weiss-Brillouin second-order magnetic phase transition from ferromagnetic to paramagnetic at Tc=173 K. The reoxidized sample Pr0.70Ba0.30MnO3.025 has two Curie temperatures due to the two coexisting but separate chemical phases, and its M(T) curves are smooth and continuous. Yet, using the Banerjee criterion we find that the oxygen stoichiometric A-site ordered PrBaMn2O6 phase actually undergoes a first-order magnetic phase transition at T c=133 K, while the oxygen non-stoichiometric A-site disordered Pr0.90Ba0.30MnO3.05 phase has its own second-order phase transition at a much higher temperature Tc=313 K. ^
Physics, Condensed Matter
Chen, Michael H, "Magnetic phase transitions in praseodymium-barium doped manganites" (2007). ETD Collection for University of Texas, El Paso. AAI1455873.