Morin-type spin-reorientation transition below the Néel transition in the monoclinic compositions of (1-x)BiFeO3-xPbTiO3 (x=0.25 and 0.27): A combined dc magnetization and x-ray and neutron powder diffraction study

Abstract

The dc magnetization M(T) studies on monoclinic compositions of (1-x)BiFeO3-xPbTiO3 (BF-xPT), x = 0.25 and 0.27, reveal another anomaly at spin-reorientation phase transition (TOPT) below the Néel transition temperature (TN). From a Rietveld refinement of the magnetic structure using neutron powder diffraction data, it is shown that the anomaly at TOPT is due to a spin-reorientation transition from a long-range magnetically ordered phase (Gy, F xz) stable at TOPT<T<TN to another long-range ordered phase (Gxz, Fy) stable below T OPT, wherein the ferromagnetic component of the noncollinear magnetic structure undergoes a spin flop. The spin-reorientation transition is not linked with any structural phase transition as confirmed by x-ray diffraction studies. Further, this transition is not accompanied with any magnetoelastic coupling. Unlike the Néel transition, the spin-reorientation transition is purely of magnetic origin. The spin-reorientation transition in BF-xPT is similar to the Morin transition in hematite and differs from the spin-reorientation transition in orthoferrites that is driven by the coupling of two magnetic sublattices. © 2013 American Physical Society.