Transition from antiferromagnetic to ferromagnetic state of systems LaMnO3+λ and La1−x
Srx(Mn1−x/2Nb
x/2)O3 |
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Authors: | I O Troyanchuk O S Mantytskaya A N Chobot H Szymczak |
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Institution: | (1) Institute of Solid-State and Semiconductor Physics, Belarussian Academy of Sciences, Minsk, 220076, Belarus;(2) Institute of Physics, Polish Academy of Sciences, 02-668 Warsaw, Poland |
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Abstract: | The crystal structure and magnetic and elastic properties of the system LaMnO3+λ are investigated for various concentrations of oxygen. Upon an increase in the oxygen concentration, the orbital-ordered phase is transformed into an orbital-disordered phase via a two-phase crystal-structure state in the interval 0.04<λ<0.06. The transition is accompanied by a jumplike increase in the Curie temperature and spontaneous magnetization. An analysis of the magnetic properties in weak fields and of the temperature dependence of the Young modulus reveals the properties typical of the orbital-ordered antiferromagnetic phase up to λ=0.08. It is proposed that the two-phase state is associated with the martensite type of the orbital order-disorder phase transformation. The system La1?x Srx(Mn1 ?x/2Nb x/2)O3 in which all manganese ions are in the trivalent state exhibits a sequence of antiferromagnetic-ferromagnetic (x>0.2) and ferromagnetic-spin glass (x>0.4) transitions. In both systems, the orbital-disordered phases are ferromagnetic, indicating the crucial role of orbital ordering in the formation of magnetic properties. |
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