Magnetic and crystallographic properties of Fe1−x(Cu0.5In0.5)xCr2S4 spinels

Fe_1?x(Cu_0.5In_0.5)_xCr₂S₄ spinel powders with 0 ≤ x ≤ 1 were prepared. Their lattice constant (a_o) increases linearly with x from a_o = 0.9995 nm for x = 0 to 1.0065 nm for x = 1. Cu⁺, In³⁺, and Fe²⁺ ions occupy tetrahedral A sites of the spinel lattice and Cr³⁺ ions the octahedral B sites. Spinels with 0 ≤ x ≤ 0.82 are ferrimagnets with Curie temperatures decreasing from 171 K for x = 0 to 116 K for x = 0.82. Spinels with 0.82< x≤ 1 are antiferromagnets with Néel temperatures between 31 K and 36 K. The magnetic moment of Fe_0.18Cu_0.41In_0.41Cr₂S₄ spinels was determined by susceptibility measurements to be 5.85 $\text{μ}{}_{\mathrm{<mtext>B</mtext>}}\text{molecule}$, which is equal to the calculated spin-only magnetic moment.     

Materials for magnetic recording derived from chromium dioxide

A new method is described for the preparation of ferromagnetic chromium dioxide by high-pressure oxidation. A new ferromagnetic ternary oxide of formula Cr_1?xRh_xO₂ (0 < x < 0.5) has also been prepared. It has a high coercive field ($\text{H}{}_{\mathrm{<mtext>C</mtext>}}\text{? 500}\text{Oe}$) at Rh contents as low as $\text{x}\text{? 0.001}$ and shows therefore promise for use in magnetic recording, especially for video applications.     

Sur un nouveau materiau pour l'enregistrement magnetique derive du dioxyde de chrome

A new ferromagnetic ternary oxide of formula Cr_1?xIr_xO₂ (0 < x < 0.3) has been prepared and ajusted. Thanks to iron doping a high coercive field ($\text{H}{}_{\mathrm{<mtext>c</mtext>}}\text{? 600}\text{Oe}$) can be obtained in appropriate conditions for an irridium content as low as $\text{x}\text{? 5.10}{}^{\mathrm{?4}}$. Such a material is promising for magnetic recording.     

Interactions magnetiques hyperfines et quadrupolaires combinees pour les ions d'impuretes 119Sn2+ dans Cr2O3

Hyperfine magnetic interactions have been observed for the first time for Sn²⁺ ions introduced as doping agents in a magnetically ordered oxide (¹¹⁹Sn: Cr₂O₃). Mössbauer resonance at low temperature shows for ¹¹⁹Sn²⁺ the simultaneous presence of hyperfine magnetic and quadrupole interactions, which have the same order of magnitude at 77 K. From the spectra, the following parameters have been determined: tranfered hyperfine magnetic field: H_Sn²⁺ (77 K = 38 ± 1kOe, sign and value of the quadrupole interaction constant: eV_zzQ = + 3,6 ± 0,3 mm/s, asymmetry parameter: η = 0,15 ± 0,05, polar (θ) and azimutal (?) angles: $\text{θ ? ? ? 90°}$, and chemical shift: $\text{δ}\text{BaSnO}{}_3\text{= + 2,89 ± 0,02}\text{mm}\text{/}\text{s}$. The investigation shows that Sn²⁺ is localized at the surface of the Cr₂O₃ grains.     

An ESR study of the heterogeneous system Cr2O3V2O5

An ESR study of the ‘products’ of the high temperature solid state reaction xCr₂O₃+yV₂O₅ ($\text{0.05≦(}\text{x}\text{y}\text{)≦2.0}$), aided by powder X-ray diffraction and IR spectra, has revealed (i) ‘unfamiliar’ paramagnetic intermediates Cr⁴⁺ and Cr⁵⁺, (ii) provided some clues to the oxidation of Cr³⁺ to Cr⁶⁺, and (iii) demonstrated a variety of exchange interactions involving V⁴⁺ and Cr³⁺.     

Magnetic,electrical and thermal studies on the V1−xMox02

The monoclinic-to-tetragonal structure transition of oxides V_1?xMo_x0₂ with $\text{0≤}\text{x}\text{≤0.20}$ has been studied by means of DTA, X-ray diffraction, magnetic susceptibility (powder samples) and electrical conductivity (single crystals) measurements within the temperature region 80 K to 400 K. A linear decrease of the transition temperature of 11 K per atom % Mo was observed. The magnetic susceptibility of the low temperature phase was found to be temperature independent paramagnetic for all preparations. Electrical conductivity measurements on the same phase showed crystals with $\text{x}\text{? 0.04}$ to be semiconducting, while a metallic behavior was observed in the region $\text{0.10 ?}\text{x}\text{? 0.14}$.     

Rutile type oxides prepared from Cr1−xFexOOH with InOOH type structure

Iron doped CrO₂ was prepared by thermal decomposition of Cr_1?xFe_xOOH with InOOH type structure which was synthesized under high temperature-pressure conditions. Charge compensation in the rutile type oxides was made by generating Cr⁵⁺ ion in the compositional range of x ≦ 0.1 and oxygen vacancy in the range of $\text{x}\text{≧ 0.15}$. The Curie temperature of rutile type oxide rose up to 162°C at x=0.1, then fell with increase of iron content. The lowest Curie temperature was 88°C at the initial composition of x=0.3. The region where the Curie temperature rises correspond to that where Cr⁵⁺ is produced, and the region where the Curie temperature drops to that where oxygen vacancy is generated.     

Flux jump in the flux creep state

Taking the magnetic diffusivity of the superconductor in the flux creep state into consideration, the maximum magnetic field differences (H_fj) at which a flux jump will occur are calculated. From our calculated results, assuming the extreme limit D_m ? D_th, H_fj will have a power dependence of between $\text{?}\text{1}\text{6}$ and $\text{?}\text{1}\text{2}$ on the magnetic field sweep rates. For low magnetic field sweep rates and good cooling conditions, the values of H_fj in the flux creep state become considerably larger than those calculated by other authors in the adiabatic state.     

The crystal structures of Ba2LaRuO6 and Ca2LaRuO6

Neutron diffraction experiments have been performed to determine the structures of Ba₂LaRuO₆ and Ca₂LaRuO₆. Both are ordered, distorted perovskites. Ba₂LaRuO₆ is monoclinic, space group $\text{P}\text{2}{}_{\mathrm{<mtext>1</mtext>}}\text{n}$ with $\text{a}{}_0\text{=6.0285(7)}\text{A}\text{?}$, $\text{b}{}_0\text{=6.0430(7)}\text{A}\text{?}$, $\text{c}{}_0\text{=8.5409(6)}\text{A}\text{?}$, β=90.44(1)^o. The A sites are occupied by barium and the B sites by an ordered arrangement of lanthanum and ruthenium. Ca₂LaRuO₆ is triclinic, space group P1 with a₀=5.6179(5), b₀=5.8350(5), c⁰=8.0667(4), α=90.0^o, β=89.76(1)^o, γ=90.0^o. The A sites are occupied by calcium and lanthanum in a disordered manner, and the B sites are occupied by an ordered arrangement of calcium and ruthenium. The results reported in this paper thus contradict those of previous workers. The low-temperature magnetic structures are discussed briefly.     

Rate law versus oxygen pressure in spinel oxidation to γ lacunar spinels

In the controlled oxidation of spinels (Fe²⁺Fe³⁺_2?xM³⁺_x)O^2?₄ (M³⁺=Al³⁺, Cr³⁺ ; 0 < x < 2) and (Fe²⁺Al³⁺_2?xCr³⁺_x)O^2?₄ to the metastable phases γ(Fe³⁺_1?yM³⁺_y)₂O^2?₃ and $\text{γ(}\text{Fe}{}^{\mathrm{3+}}{}_{\mathrm{<mtext>1</mtext><mtext>3</mtext>}}\text{Al}{}^{\mathrm{3+}}{}_{\mathrm{<mtext>2</mtext><mtext>3</mtext><mtext>?</mtext><mtext>y</mtext>}}\text{Cr}{}^{\mathrm{3+}}{}_{\mathrm{<mtext>y</mtext>}}\text{O}{}^{\mathrm{2?}}{}_{\mathrm{3?}}\text{(0 <}\text{y}\text{<}\text{2}\text{3}\text{)}$, over the temperature range 200–450°C, the rate law is usually v = k Pⁿ_(O2) with $\text{n}\text{=}\text{1}\text{2}$. This law is well interpreted if we consider a total association vacancy-positive charge. However, for low oxidation extents a (a < 0.3) the law written as is in better agreement with a partial association of defects. For a total dissociation of defects exponent n of the pressure law is always smaller.     

Une modelisation du comportement magnetique d'un compose de l'iridium pentavalent: LaLi12Ir12O3

A new interpretation is proposed for the magnetic properties of perovskite-type iridium (+V) oxide $\text{LaLi}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{Ir}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{O}{}_3$. In its unusual +5 oxidation state iridium has a t⁴_2ge⁰_g configuration. The magnetic susceptibility has been calculated assuming cubic symmetry of the crystal field and a Coulomb repulsion of the same order of magnitude than spin-orbit coupling. Fitting of the experimental data leads to a single spin-orbit constant $\text{ζ ? 3470}\text{cm}{}^{\mathrm{?1}}$ close to that of previously investigated Ir(+V) compounds.     

Etude de la structure cristallographique et magnetique de Cu2FeGeS4 et remarque sur la structure magnetique de Cu2MnSnS4

Single crystal X ray diffraction shows that synthetic briartite Cu₂FeGeS₄ belongs to space group I 4&#x0304; 2 m. Powder neutron diffraction allows the determination of the propagation vector $\text{k}$ and of some features of the magnetic structure. $\text{k}\text{= [}\text{1}\text{2}\text{O}\text{1}\text{2}\text{]}$ as in Cu₂MnSnS₄. The degeneracies of the magnetic structures compatible with observations are discussed.     

Metal-ion distribution and magnetic structure of Fe-substituted cobaltite spinel: FeCo2O4

The metal ion distribution of FeCo₂O₄ (cubic spinel) which was quenched from 900°C in air was determined to be ($\text{Fe}$³⁺_0.18$\text{Co}$²⁺_0.82) [$\text{Fe}$³⁺_0.82$\text{Co}$²⁺_0.18 Co^III+_1.0] O₄ with the neutron diffraction method. The oxygen spacial parameter u was determined to be 0.382 ± 0.002. The magnetic structure was explained as a Néel type ferrimagnet and the origin of the spontaneous magnetization was attributed to the uncompensation of the spins between A- and B-site of the spinel lattice. The magnetic moment per molecule was estimated to be 0.70 μB.     

Electrical properties of sintered EuZrO3  EuNbO3 and EuNbO3

Electrical resistivity of two-phase products [yEuZrO₃ + (1 ? y) EuNbO₃] increased continuously with y, and a transition from a metallic to semiconducting characteristic occured at y = 0.14. The resistivity varied almost linearly with temperaure in the range y = 0 to y = 0.24, and thermal coefficients of resistivity at 300 K for the products decreased from +5.9 × 10^?4 K^?1 to ?7.4 × 10^?4 K^?1 according to the value of y. At y = 0.14, the thermal coefficient was almost zero. Thermal coefficients of electrical resistivity for the niobates with various oxygen contents were all positive in the range $\text{2.55 <}\text{O}\text{Nb}\text{< 3.24}$ and exhibited a sharp minimum at $\text{O}\text{Nb}\text{= 2.92}$. In all these niobates, Eu_xNbO₃ was a major phase and Eu₃NbO₆ or EuNbO₂ was detected as a second phase in the range $\text{O}\text{Nb}\text{> 3}$ or $\text{O}\text{Nb}\text{< 3}$ respectively. Peaks in the resistivity curves were correlated with a magnetic ordering temperature for samples with an overall ratio $\text{O}\text{Nb}\text{> 3}$.     

Sur la phase CsVCl3: Etude cristallographique et magnetique

The crystal structure of CsVCl₃ has been determined by means of a Patterson synthesis and refined by full-matrix least-squares to a residual R = 0.06. The space group is $\text{P}\text{6}{}_3\text{mmc}$ with $\text{a}\text{= 7.228 (3)}\text{A}\text{?}$ and $\text{c}\text{= 6.030 (3)}\text{A}\text{?}$. The structure of CsVCl₃ belongs to the CsNiCl₃ type. The magnetic properties have been interpreted on the basis of a $\text{S}\text{=}\text{3}\text{2}$ model for Heisenberg one-dimensional interactions. The strong antifer-romagnetic intrachain V-V interactions ($\text{J}\text{k}\text{= ?115}\text{K}$) seem to result from direct t_2g - t_2g coupling and from 90° correlation superexchange coupling using the 3s chlorine orbital.     

Hydromagnetic stability of helical flows permeated by a magnetic field with a radial component

In this paper, we have studied the linear stability of the nondissipative helical flow of an incompressible perfectly conducting fluid between two concentric cylinders permeated by a non-zero radial magnetic field. It is found that a rigidly rotating column of a perfectly conducting fluid permeated by a magnetic field [($\text{A/r}$), ($\text{C/r}$), $\text{B}{}_0$], where $\text{A, C, B}{}_0$ are constants, is stable for all infinitesimal disturbances.     

Electrical properties of ferromagnetic Gd3−xS4 near its Curie temperature

Nonstoichiometric $\text{Gd}{}_{\mathrm{<mtext>3?</mtext><mtext>x</mtext>}}\text{S}{}_4\text{(0 <}\text{x}\text{<}\text{1}\text{3}\text{)}$, which exhibits a metallic behavior, was obtained by heating an insulating Gd₂S₃ at various temperatures under a vacuum. Electrical and magnetic properties of the samples obtained have been investigated from 4.2 K to 300 K. A maximum in resistivity was observed in the curve of resistivity vs. temperature. The temperature T_P, at which the maximum emerged, was very close to the Curie temperature T_C for the sample. An increase in resistivity at T_P, Δ_?, is proportional to ?_P exp ($\text{E}\text{k}{}_{\mathrm{B}}\text{T}{}_{\mathrm{P}}$), where ?_P is the resistivity obtained by the extrapolation from the linear portion to T_P in the ? vs. T curve. Using the relationship obtained, a model based on the formation of magnetic polaron was proposed for this system.