Non-zero spontaneous magnetic moment along crystalline b-axis for rare earth orthoferrites

Rare earth orthoferrites demonstrate great application potentials in spintronics and optical devices due to their multiferroic and magnetooptical properties. In RFeO3, magnetic R3+ undergo a spontaneous spin reorientation in a temperature range determined by R (rare earth), where the magnetic structure changes from Gamma (2) to Gamma (4). The b-axis component of their magnetic moment, M-b, is reported in numerous neutron diffraction studies to remain zero at all temperatures. More sensitive magnetometer measurements reveal a small non-zero M-b, which is minute above similar to 200K. M-b increases with cooling and reaches values of similar to 10(-3)mu (B)/f.u. at temperatures within or below the spin reorientation temperatures. Our results can be explained by assuming the Fe3+ spins as the origin of non-zero M-b, while R3+ spins suppress M-b. The representation analysis of point groups shows that non-zero M-b is associated with a small admixture of the Gamma (3) phase to Gamma (2) or Gamma (4). Such a mixing of the three magnetic phases requires at least a fourth order of the spin Hamiltonian for RFeO3 to describe the non-zero M-b.