Spin-Reorientation Transition Driven by Double Exchange in CeFeO₃ Ceramics

Spin-reorientation (SR) transition as a kind of magnetic phase transition is the most peculiar and interesting phenomenon for rare-earth orthoferrites RFeO 3, the research on which is important not only for practical applications but also for physical theory. In this article, we report a new and novel second-order SR transition Γ 4 (G x, A y, F z ) → Γ 2 (F x, C y, G z ) at around T SR2 = 126 K, besides the normal first-order SR transition Γ 4 (G x, A y, F z ) → Γ 1 (A x, G y, C z ) at around T SR1 = 230 K, in orthoferrite CeFeO 3 induced by intrinsic doping with oxygen ions. The twofold SR transition of type Γ 4 → Γ 41 → Γ 42 for the Fe 3+ magnetic sublattices in CeFeO 3 shows different natures. By the result analyses of magnetism and specific heat, it is confirmed that the first-order SR transition Γ 4 → Γ 1 is attributed to the Ce 3+ –Fe 3+ ferromagnetic (FM) interaction, but the second-order SR transition at T SR2 = 126 K is ascribed to the Fe 2+ –Fe 3+ double-exchange FM interaction in Fe sublattices due to the substitution of nonmagnetic Ce 4+ ions with magnetic Ce 3+ ions and the valence fluctuation in R sublattices. This new mechanism is different from that for Dy 0.5 Pr 0.5 FeO 3 and Mn-doped SmFeO 3 with a twofold SR transition. Both Ce 3+ –Fe 3+ and Fe 2+ –Fe 3+ FM interactions in CeFeO 3 have an effect on the free energy. The combination and competition of Ce 3+ –Fe 3+ and Fe 2+ –Fe 3+ FM interactions dominate the SR transition taking the first-order one (Γ 4 → Γ 1 ) or the second-order one (Γ 4 → Γ 2 ), which can be adjusted by both the distributions of the magnetism and valent states of R ions in the R-site of orthoferrites RFeO 3 .