ABSTRACT
The modulated crystal structure and modulated magnetic ordering of the multiferroic CaCu(x)Mn(7-x)O(12) is studied by analysing neutron and synchrotron-radiation (SR) powder diffraction data with a model based on the magnetic superspace group R31'(00γ)ts. Both atomic position modulations and magnetic modulations are described with the modulation vector (0, 0, q). The magnetic ordering is a screw-type circular helix where the magnetic moments are perpendicular to the c direction. The temperature dependence of the modulation vector length and the ordered magnetic moments of Mn(3+) and Mn(4+) ions is given between T = 50 K and the Néel temperature T(N) is approximately equal to 90 K. The atomic position modulation length L(p) and the magnetic modulation length L(m) fulfil the relation L(m) = 2L(p) at all temperatures between 50 K and T(N).
ABSTRACT
Low temperature atomic position modulations and magnetic moment modulations are reported for CaCu(x)Mn(7 - x)O(12) (x = 0.0, 0.1 and 0.23) using neutron powder diffraction. Both modulations are described with propagation vectors (0, 0, q) parallel to the c-axis in the hexagonal setting. The present neutron diffraction studies confirm the quantitative model describing the atomic position modulations in CaCu(x)Mn(7 - x)O(12) (x = 0.0 and 0.1) as derived from synchrotron based powder x-ray diffraction studies (Slawinski et al 2009 Acta Crystallogr. B 65 535). Neutron diffraction studies confirm the relation between the atomic position modulation length L(p) and the magnetic modulation length L(m) = 2L(p) between 50 K and the Néel temperature T(N). CaCu(x)Mn(7 - x)O(12) (x = 0.1 and 0.23) shows a magnetic phase transition near 50 K associated with considerable changes of the magnetic modulation length and the magnetic coherence length, similar to that observed in the parent CaMn(7)O(12).
ABSTRACT
Application of the neutron scattering technique in the study of crystal and magnetic properties of multiferroic BiFeO(3) is presented. The crucial role of the neutron scattering technique, complementary to X-ray diffraction method and transmission electron microscopy, is shown. Especially the ultra high-resolution time-of-flight (TOF) neutron diffraction technique used by Sosnowska et al. to detect the magnetic cycloid ordering and its role in studies of physical properties of BiFeO(3) and its alloys are reviewed. The first inelastic neutron scattering patterns of magnetic excitations in BiFeO(3) are also presented. Applications of different microscopy techniques such as transmission electron microscopy (TEM), scanning electron microscopy (SEM), field emission TEM and SEM (FESEM and FETEM), magnetic force microscope (MFM) and polarization force microscopy (PFM) bring insight on the fundamental problem of ferroelectricity and confirm the potential of BiFeO(3) multiferroic material for nanoscale devices.
ABSTRACT
The modulation of atomic positions in CaCu(x)Mn(7-x)O12 (x = 0 and 0.1) was studied using synchrotron radiation powder diffraction below 250 and 220 K, respectively. The copper-rich member CaCu(x)Mn(7-x)O12 (x = 0.23) does not show any modulation of the atomic positions at temperatures as low as 10 K. Using low-temperature neutron powder diffraction the modulation of the magnetic moments of Mn ions in CaCu(x)Mn(7-x)O12 (x = 0, 0.1 and 0.23) has been investigated. Long-range modulated magnetic ordering in CaCu(x)Mn(7-x)O12 (x = 0, 0.1 and 0.23) is observed below 90.4, 89.2 and 78.1 K. (0,0,q(p)) and (0,0,q(m)) are the propagation vectors describing the modulations of the atomic positions and the magnetic moments. For CaCu(x)Mn(7-x)O12 (x = 0 and 0.1) the magnetic modulation and atomic modulation lengths are related by a factor of 2 satisfying the relation (1-q(p)) = 2(1-q(m)).
ABSTRACT
The parameters of the crystal structure of BiFeO(3), described within the space group R3c, have been determined by high-resolution neutron powder diffraction for temperatures from 293 to 923 K. It was found that there is a local minimum for the rhombohedral angle alpha(rh), near the Néel temperature T(N) approximately 640 K, a gradual rotation of the FeO(6) octahedra and an increase of the Fe-O-Fe angle. The displacement of the Bi(3+) ions from the FeO(6) octahedra which influence the electric polarization decreases with temperature. One of the Bi-Fe distances also has a local maximum near T(N). The atomic vibrations of Bi(3+) and O(2-) ions show a significant anisotropy.
