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Members of the jarosite mineral family AFe3(OH)6(SO4)2, where A is usually a univalent cation, posses a highly frustrated Kagome lattice of antiferromagnetically coupled S = 1 5 Heisenberg moments. All the members of the family show-long range magnetic order below T N ≊ 55 K except for the hydronium salt (A  H3O) which displays a spin-glass-like transition at T f ≊ 15 K . The only clear difference between the two sets if materials is that all the salts except for hydronium salt have a strong tendency to lose iron atoms from the structure when it is synthesized. When 11% of the magnetic sites are removed or replaced with diamagnetic ions in the diluted salt (D3O)Fe3−xAlx(OD)6(SO4)2, Tf rises to 25.5 K and powder neutron diffraction reveals both short- and long-range magnetic correlations at 1.4 K.

A rich variety of magnetoelastic effects have been investigated as a function of temperature by means of neutron diffraction and transport measurements in insulating ( x = 0.10) and metallic ( x = 0.15, 0.25, 0.33 and 0.40) La 0.85− x Y 0.15 Ca x MnO 3 manganites. The coupling between the charges, spins and lattice at low temperatures brings about modifications in the s ab strain for x = 0.10, negative thermal expansion coefficients for x = 0.25, and modifications in the residual Jahn-Teller distortion ( x = 0.33).

Substitution of Mn for Fe in Ce2Fe17 strongly suppresses the ferromagnetic ground state, changing it into an antiferromagnetic one. However, a state of spontaneous magnetization is re-entered in the Ce2Fe17−xMnx compounds when the Mn content reaches x=1.3. Magnetic structures and magnetic interactions in the re-entrant ferromagnetic Ce2Fe15.3Mn1.7 compound have been studied using both microscopic (neutron powder diffraction in magnetic fields of up to 0.7T) and macroscopic (ac susceptibility and magnetization measurements under high pressures of up to 8kbar in magnetic fields of up to 5T) techniques. A spiral magnetic structure distorted by the presence of an in-plane ferromagnetic component is found below TN=182K. Enhancement of the ferromagnetic interactions leads to a steep transformation of the magnetic spiral to a magnetic structure with nonzero spontaneous magnetization below ΘT=59K. This structure is described by a distorted elliptical spiral model with an incommensurate propagation vector along th...

The magnetic properties of low-doped Bi1−xSrxMnO3 manganites (x

This work presents an investigation of the central role of oxygen on the physical properties of highly ordered layered cobaltites. It includes the study of the structural and magnetic properties of PrBaCo2O5+δ compounds with high oxygen content (0.5⩽δ⩽0.90), with special emphasis on PrBaCo2O5.75. For δ=0.75 the ordering of oxygen vacancies gives rise to a tetragonal (P4∕mmm) structure with a≈c≈2ap. On cooling, a ferromagnetic spin alignment precedes the apparition of antiferromagnetic order (canted G-type). The compounds are ferromagnetic for δ⩾0.80. Measurements on PrBaCo2O5.75 support that, above the magnetic ordering temperature, Co3+ ions in octahedral environment are in HS state.

The magnetization avalanches under field have been investigated at low temperature in Pr0.50Ca0.50Mn1−xNixO3 (x=0.05). In zero field, a 5% of Ni at the Mn site provokes the coexistence of three types of magnetic∕structural mesoscopic domains at low temperature: ferromagnetic metallic (majority phase), pseudo-CE and CE-type (minority phase). The ultrasharp steps observed in the low-temperature isothermal magnetization and resistivity curves were investigated by neutron powder diffraction in magnetic fields up to 5T. At 3T an abrupt growth of ferromagnetic microclusters occurs at the expenses of the two types of antiferromagnetic orbital-ordered domains (CE and pseudo-CE regions).

Hydrogen insertion compounds of V 9 Mo 6 O 40 have been synthesized and investigated using incoherent inelastic neutron scattering (IINS) vibrational spectroscopy. IINS spectra of H x V 9 Mo 6 O 40 (x=7.8 and 17.5) confirm that in both phases H is present as coordinated hydroxyl groups. There is no evidence for the presence of coordinated water in contrast to the hydrogen insertion compounds of MoO 3 and V 2 O 5 .

Colossal magnetoresistance has been observed in polycrystalline Gd0.5Sr0.5MnO3 perovskite. Irreversibility and sharp anomalies in the magnetostriction, magnetization, and magnetoresistance isotherms take place at low temperatures (

Magnetization, heat capacity, and neutron diffraction experiments on the \ensuremath{\beta}-phase of the dithiadiazolyl radical, p-NC.${\mathrm{C}}_{6}$${\mathrm{F}}_{4}$.CNSSN., provide conclusive evidence that this system exhibits noncollinear antiferromagnetism at 35.5 K, an unprecedented temperature for an organic radical. On the basis of magnetization and powder neutron diffraction results, coupled with theoretical calculations of the spin distribution within the molecule, a magnetic structure for this compound is proposed in which the interactions propagate through $\mathrm{S}\dots{}\mathrm{N}$ contacts.

The ternary indium palladium intermetallics In3Pd5, InPd2, and InPd3 have been synthesized by iodine-catalyzed reactions from the elements. Rietveld refinements on X-ray powder diffraction patterns provide the first accurate crystal structure data for In3Pd5 (Pbam, No. 55, a = 1104.20(2), b = 561.346(8), c = 424.263(6) pm, Rh5Ge3-type) and InPd2 (Pnma, No. 62, a = 561.676(6), b = 421.710(4), c = 822.78(8) pm, Co2Si-type). X-Ray powder diffraction apparently confirms the TiAl3 structure type proposed in the literature for InPd3. However, Rietveld refinement on neutron powder diffraction data reveals an In/Pd distributional disorder. Therefore, we describe the crystal structure of InPd3 in a AuCu-type model instead (P4/mmm, No. 123, a = 287.224(4), c = 380.079(7) pm), with mixed occupancy of one crystallographic site by 50% In and 50% Pd. In contrast to In3Pd5 and InPd2, which can be considered to be line compounds, InPd3 shows a non-negligible homogeneity range with unit cell volumes ranging from 0.126132(5) nm3 for the indium-rich to 0.125474(8) nm3 for the palladium-rich In1+xPd3−x phases. Mean In-Pd distances in these indium palladium intermetallics range from 272.3 pm (In1 in In3Pd5) with coordination number 8 for indium to 281.2 pm for 12-coordinated In in InPd3.

The anhydrous alum KTi(SO4)(2), where the Ti3+ (d(1), S = 1/2) ions form an anisotropic triangular lattice, has been prepared by a new hydrothermal route and characterized by magnetic susceptibility and neutron scattering measurements. Contrary to expectations, fits to the magnetic susceptibility indicate that the spins are isotropic (i.e. Heisenberg) and that the frustrating couplings are weak; indeed, the system is well modelled by nearly isolated chains. The inelastic neutron scattering data furthermore shows excellent agreement with an exact theoretical calculation for the one-dimensional spinon continuum. The unexpected magnetic properties of KTi(SO4)(2) are explained in the light of density functional calculations, which reveal an unusual orbital ground state for the Ti3+ ion.

Manganese perovskites based on the compound LaMnO3 are attracting considerable theoretical and technological interest by virtue of their unusual magnetic and electronic properties1–4. Most notable of these properties is the extremely large change in resistivity that accompanies the application of a magnetic field, an effect known as 'colossal' magnetoresistance. The origin of this effect has been attributed5–7 to the presence of magnetic polarons—charge carriers accompanied by a localized (and magnetically polarized) distortion of the surrounding crystal lattice8,9— but their existence and properties remains a matter of speculation. Here, using a combination of volume thermal expansion (with and without an applied field), magnetic susceptibility and small-angle neutron scattering measurements, we present evidence for the existence of magnetic polarons above the ferromagnetic ordering temperature, Tc. We detect the spontaneous formation of localized ∼12-A magnetic clusters above Tc which, on application of a magnetic field, grow in size but decrease in number. We argue that the response of these magnetic polarons to an applied magnetic field underlies the pronounced magnetoresistive properties in the compounds (La1–xAx)2/3Ca1/3MnO3 (where A is Y or Tb).

The rich and peculiar macro- and microscopic phenomenology observed in the electron-doped region of the Sm-Ca phase diagram of manganites can he found in the unique and fascinating compound Sm 0 . 1 5 Ca 0 . 8 5 MnO 3 . We report the existence of nano- and microscopic phase segregation above and below T N 112 K. The very different nature of the coexisting phases and the field and temperature dependencies are explained considering the interplay of magnetic and structural correlations, which give rise to different structural and magnetic ground states, close in energies (P-Pnma, G+F-Pnma, G-Pnma, C-P2 1 /m).