The magnetic structure of YMnO3 perovskite revisited

The magnetic structure of the orthorhombic perovskite YMnO3 has been investigated. A study on a polycrystalline sample based on neutron diffraction data and magnetization measurements has shown that YMnO3 becomes magnetically ordered below T-N = 42 K. In the space group Pnma, the sinusoidal magnetic structure is defined by a (C-x, 0, 0) mode and characterized by the propagation vector k = (k(x), 0, 0). The k(x)-component increases from 0.420(4), immediately below the ordering temperature, to 0.435(2) at T = 28.7 K. Below 28 K the k(x)-component remains unchanged. The sinusoidal spin arrangement remains stable down to 1.7 K; at this temperature the amplitude of the sinusoid is A(k) = 3.89(6) mu(B). YMnO3 is the most distorted perovskite of the RMnO3 series (R = rare earths); the observed sinusoidal magnetic structure is in contrast with those exhibited by the less-distorted members (i.e. LaMnO3), which are commensurate-type antiferromagnetic structures.