Magnetic structure

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

Structural, dielectric, magnetic, and nuclear magnetic resonance studies of multiferroic Y-type hexaferrites

Abstract: The effect of strontium substitution on structural, magnetic, and dielectric properties of a multiferroic Y-type hexaferrite (chemical formula Ba2−xSrxMg2Fe12O22 with 0 ≤ x ≤ 2) was investigated. Y-type hexaferrite phase formation was not affected by strontium substitution for barium, in the range 0 ≤ x ≤ 1.5, confirmed by x-ray diffraction and Raman spectroscopy measured at room temperature. Two intermediate magnetic spin phase transitions (at tempertures TI and TII) and a ferrimagnetic-paramagnetic transition (at Curie temperature TC) were identified from the temperature dependence of the magnetic susceptibility. Magnetic transition temperatures (TI, TII, and TC) increased with increasing strontium content. Magnetic hysteresis measurements indicated that by increasing strontium concentration, the coercivity increases, while the saturation magnetization decreases. The 57Fe NMR spectrum of the Y-type hexaferrite measured at 5 K and in zero magnetic field showed remarkable differences compared to that of o...

Structural Tuning of Charge, Orbital, and Spin Ordering in Double-Cell Perovskite Series between NdBaFe2O5 and HoBaFe2O5

Abstract: Charge, orbital, and magnetic ordering of NdBaFe(2)O(5) and HoBaFe(2)O(5), the two end-members of the double-cell perovskite series RBaFe(2)O(5), have been characterized over the temperature range 2-450 K, using differential scanning calorimetry, neutron thermodiffractometry and high-resolution neutron powder diffraction Upon cooling, both compounds transform from a class-III mixed valence (MV) compound, where all iron atoms exist as equivalent MV Fe(25+) ions, through a "premonitory" charge ordering into a class-II MV compound, and finally to a class-I MV phase at low-temperature The latter phase is characterized by Fe(2+)/Fe(3+) charge ordering as well as orbital ordering of the doubly occupied Fe(2+) d(xz) orbitals The relative simplicity of the crystal and magnetic structure of the low-temperature charge-ordered state provide an unusual opportunity to fully characterize the classical Verwey transition, first observed in magnetite, Fe(3)O(4) Despite isotypism of the title compounds at high temperature, neutron diffraction analysis reveals striking differences in their phase transitions In HoBaFe(2)O(5), the Verwey transition is accompanied by a reversal of the direct Fe-Fe magnetic coupling across the rare earth layer, from ferromagnetic in the class-II and -III MV phases to antiferromagnetic in the low-temperature class-I MV phase In NdBaFe(2)O(5), the larger Nd(3+) ion increases the Fe-Fe distance, thereby weakening the Fe-Fe magnetic interaction This decouples the charge and magnetic ordering so that the Fe-Fe interaction remains ferromagnetic to low temperature Furthermore, the symmetry of the charge-ordered class-I MV phase is reduced from Pmma to P2(1)()ma and the magnitude of the orbital ordering is diminished These changes destabilize the charge-ordered state and suppress the temperature at which the Verwey transition occurs A comparison of the magnetic and structural features of RBaFe(2)O(5) compounds is included in order to illustrate how structural tuning, via changes in the radius of the rare-earth ion, can be used to alter the physical properties of these double-cell perovskites

Magnetic structure of bixbyite α -Mn 2 O 3 : A combined DFT + U and neutron diffraction study

Abstract: First-principles density functional theory DFT$+U$ calculations and experimental neutron diffraction structure analyses were used to determine the low-temperature crystallographic and magnetic structure of bixbyite $\ensuremath{\alpha}$-Mn${}_{2}$O${}_{3}$. The energies of various magnetic arrangements, calculated from first principles, were fit to a cluster-expansion model using a Bayesian method that overcomes a problem of underfitting caused by the limited number of input magnetic configurations. The model was used to predict the lowest-energy magnetic states. Experimental determination of magnetic structure benefited from an optimized sample synthesis, which produced crystallite sizes large enough to yield a clear splitting of peaks in the neutron powder diffraction patterns, thereby enabling magnetic-structure refinements under the correct orthorhombic symmetry. The refinements employed group theory to constrain magnetic models. Computational and experimental analyses independently converged to similar ground states, with identical antiferromagnetic ordering along a principal magnetic axis and secondary ordering along a single orthogonal axis, differing only by a phase factor in the modulation patterns. The lowest-energy magnetic states are compromise solutions to frustrated antiferromagnetic interactions between certain corner-sharing [MnO${}_{6}$] octahedra.

Preparation, crystal and magnetic structure, and magnetotransport properties of the double perovskite CaCu2.5Mn4.5O12

Abstract: CaCu2.5Mn4.5O12 perovskite has been prepared in polycrystalline form under moderate pressure conditions of 20 kbar, in the presence of KClO4 as oxidizing agent. This material has been studied by X-ray and neutron powder diffraction (NPD), magnetic, magnetotransport, and thermopower measurements. The crystal structure is cubic, space group Im3 (No. 204), with a = 7.2279(1) A at room temperature (RT). In the ABO3 perovskite superstructure, the A positions are occupied by Ca2+ and (Cu2.52+Mn0.53+), ordered in a 1:3 arrangement giving rise to the body-centering of the unit cell. At the B positions, Mn adopts a mixed oxidation state of 3.875+; MnO6 octahedra are considerably tilted by 19°, due to the relatively small size of the A-type cations. The Curie temperature is 345 K. Low temperature (2 K) NPD data show evidence for a ferrimagnetic coupling between Mn3.875+ and (Cu2.52+Mn0.53+) spins, with ordered magnetic moments of 2.32(5) and −0.54(3) μB, respectively. An additional canting effect of the Mn moments...