Magnetic structure

About: Magnetic structure is a research topic. Over the lifetime, 10787 publications have been published within this topic receiving 207143 citations.

Magnetism in iron as a function of pressure

Abstract: Magnetism in iron plays a central role in understanding the physical properties of its polymorphs, including the close-packed high pressure phases. We explore the rich and complex magnetic structures of these phases in two ways. We use a first-principles based, magnetic tight-binding total energy model to study non-collinear magnetic structures, and an all-electron method to study the collinear state in hcp iron that we predict in the hcp iron stability range. For the non-collinear study we compute the magnetization energy and moments for various non-collinear ordered spin configurations. For fcc iron we find non-collinear structures with a wavevector (0,0,q) with q close to 0.5 to be energetically stable, in agreement with previous first-principles calculations. In the high pressure stability field of hcp iron we find a stable collinear antiferromagnetic structure (afmII), previously predicted with an all-electron method. We further investigate the afmII structure, computing physical properties from first principles that support the notion of antiferromagnetic correlations in hcp iron. We show that a recently observed anomalous splitting in Raman spectra of hcp iron under compression can be quantitatively explained by spin?phonon interactions. To address the absence of M?ssbauer splitting in experiments on hcp iron we have also calculated the hyperfine field of afmII iron and find it to be so small that the predicted splitting would be smaller than the resolution limit of experiments.

Magnetic properties of the S = 1/2 quasi-one-dimensional antiferromagnet CaCu2O3

Abstract: We report single crystal growth and magnetic susceptibility and neutron diffraction studies of the S=1/2 quasi-1D antiferromagnet CaCu2O3. The structure of this material is similar to that of the prototype two-leg spin-ladder compound SrCu2O3. However, the Cu-O-Cu bond angle in the ladder rungs in CaCu2O3 is equal to 123 deg, and therefore the magnetic interaction along the rungs is expected to be much weaker in this material. At high temperatures, the magnetic susceptibility of CaCu2O3 can be decomposed into a contribution from 1D antiferromagnetic chains of finite-size chain segments together with a weak Curie contribution. The intrachain magnetic exchange constant, determined from the magnetic susceptibility measurements, is 2000 K. CaCu2O3 undergoes a Neel transition at T_N=25 K with ordering wavevector of (0.429(5), 0.5, 0.5). The magnetic structure is incommensurate in the direction of the frustrated interchain interaction. Weak commensurate (0.5, 0.5, 0.5) magnetic peaks are also observed below T_N. Application of a magnetic field induces a metamagnetic transition at which the incommensurability of the magnetic structure is substantially reduced. The material possesses only short-range magnetic order above the transition field.

Structure of Nickel Chromite

Abstract: Nickel chromite is a normal spinel whose structure has a tetragonal distortion below about 310°K. The structure parameters have been determined by neutron diffraction at 77°K, at which temperature the c/a ratio of a face-centered unit cell is 1.04. The space group is I41/amd with four Ni ions in positions 4(a), eight Cr ions in positions 8(d), and 16 O ions in positions 16(h) with y = 0.239 and z = 0.392. The two independent Cr-O distances are 1.98 A and 1.99 A, indicating that the octahedron is not greatly distorted. The tetrahedron around the nickel is elongated by nearly 14% parallel to the c axis. Below a Curie temperature of about 65°K, nickel chromite has a small ferromagnetic moment. The neutron diffraction pattern at 4.2°K shows extra peaks which can be indexed on the basis of a primitive cell having the same dimensions as the body-centered chemical cell. The intensities of these peaks cannot be accounted for by any simple model for the magnetic structure. In fact, a systematic search of possible ...

Room temperature antiferromagnetic order in superconducting XyFe2 − xSe2 (X = Rb, K): a neutron powder diffraction study

Abstract: Magnetic and crystal structures of superconducting XyFe2 ? xSe2 (X = Rb and?K with Tc = 31.5 and 29.5?K) have been studied by neutron powder diffraction at room temperature. Both crystals show an ordered iron vacancy pattern and the crystal structure is well described by the I4/m space group with the lattice constants a = 8.799, c = 14.576 and a = 8.730, c = 14.115???and the refined stoichiometry x = 0.30(1), y = 0.83(2) and x = 0.34(1), y = 0.83(1) for Rb and K crystals, respectively. The structure contains one fully occupied iron position and one almost empty vacancy position. Assuming that the iron moment is ordered only on the fully occupied site we have sorted out all eight irreducible representations (irreps) for the propagation vector k = 0 and have found that irreps ?2 and ?7 fit the experimental data well with the moments along the c axis. The moment amplitudes amounted to 2.15(3)??B, 2.55(3)??B for ?2 and 2.08(6)??B, 2.57(3)??B for ?7 for Rb and K crystals, respectively. Irrep ?2 corresponds to the Shubnikov group I4/m' and gives a constant moment antiferromagnetic configuration, whereas ?7 does not have a Shubnikov counterpart and allows two different magnetic moments in the structure.