This paper reviews crystal structures of ternary manganese oxides and their implications for magnetic properties. We point out the critical role of the counter-cation (A) size in driving given stoichiometries to different structure types, in particular AMnO(3) compositions to ilmenite or perovskite structure, or A(2)MnO(4) ones to spinel or K2NiF4 type. Mn2+ lies near the size borderline. It occupies the large site in A(2)Mn(2)O(4) pyrochlores, contrary to Mn4+, and occupies separate crystallographic sites in known mixed-valent Mn2+ - Mn3+ or (4+) oxides. The bond distances, Mn-O-Mn bonding angles and Mn sublattice topology are given for the main A-Mn-O structures. Only the perovskite and K2NiF4 structures give Mn-O-Mn angles near 180degrees, while these are close to 90degrees in spinels, to 135degrees in pyrochlores and marokites. The magnetic properties of non-perovskite manganese oxides are briefly discussed in view of these structural features.

This paper reports a neutron powder diffraction (NPD) study of polycrystalline marokite-type oxide CaMn2O4 as a function of temperature in the range 1.5–280 K, together with magnetization measurements up to 8 T and 800 K. The orthorhombic room-temperature structure (space group Pbcm) is confirmed. Manganese atoms are located in distorted octahedral sites with four short and two long distances at respectively 1.90–1.95 and 2.35–2.44 Å, in agreement with the Jahn–Teller character of Mn3+ ions. Below TN=220 K, this compound orders antiferromagnetically. The magnetic unit cell requires a doubling of the crystallographic a-axis. The magnetic structure has been determined by Rietveld refinement and group theory considerations. The most probable spin arrangement is found to belong to the Γ2 irreducible representation in the Pbca space group.

Substitution of Mn for Fe in the orthorhombic compound CaFe2O4 has been achieved by solid-state reactions at 1100 degreesC in air up to the composition Ca(Fe1.6Mn0.4)O-4. The evolution of cell and atomic parameters was determined from X-ray powder data using the Rietveld method. The results show that the presence of the Jahn-Teller ion Mn3+ distorts the Fe1 octahedral site and that Mn most probably occupies the Fe2 site. With increasing Mn content, the magnetism evolves from antiferromagnetic to ferrimagnetic, with Curie temperature (T-C) values (194-209 K) well above the Neel temperature of CaFe2O4 ( 160 K). A correlation between the evolution of T-C and the deviation of the Fe2-O-Fe2 angle from 90degrees is established.

Structural and magnetic properties of Pr1−xAxMnO3 (A=Na, K) are studied. Solid state reactions with alkali metal excess allowed preparation of samples with x up to 0.14 for K and 0.19 for Na. All members of this series are orthorhombic at room temperature, space group Pbnm, with orthorhombic distortion decreasing with increasing alkali metal content. Magnetic studies show a transition from antiferromagnetism in pure PrMnO3 to canted magnetic arrangement for ∼12% Mn4+ to ferromagnetism in the range 26–38% Mn4+. Curie temperatures strongly depend on substitution: they initially increase with doping level up to an optimum x≈0.15, corresponding to 30% Mn4+, and seem to decrease for higher sodium doping level.

The effect of cationic mismatch at the A site on the structural, electrical and magnetic properties of alkali-substituted Pr0.85A0.15MnO3 (A=Na, K) was investigated by varying the K/Na ratio at constant substitution level 0.15. This system encompasses remarkable structural changes: the pure sodium and potassium phases have O-type and O′-type orthorhombic structures, respectively, while intermediate compositions are almost undistorted (pseudo-cubic). All samples are ferromagnetic with a rather weak dependence of Tc, on x (dTc/dx=5K) Resistivity measurements show a semiconducting-like hopping behaviour. No metal-insulator transition is observed at the magnetic transition temperature Tc. The CMR effect reaches a maximum at Tc. The magnetic and transport properties in the paramagnetic regime are discussed in the framework of a magnetic polaron model. These results illustrate the counterbalancing effect of the average A-site cation size 〈rA〉 and of the variance in 〈rA〉.

We report on the magnetotransport properties of the Tl2Mn(2-x)Ru(x)O(7) pyrochlore as a function of the substitution degree 0 x less than or equal to 2 . The evolution of the paramagnetic moment as a function of x in this series of samples points to an itinerant character of the Ru 4d electrons for x less than or equal to 1. For larger values of x some localization of Ru 4d electrons sets in and its contribution to the paramagnetic moment is detected. The appearance of a magnetic moment in Ru atoms promotes a remarkable magnetic irreversibility, which is attributed to the reinforcement of nearest-neighbor antiferromagnetic interactions within the Mn/Ru-O sublattice and the concomitant magnetic frustration. In agreement with this hypothesis, the ferromagnetic transition temperature T-c and the saturation magnetization M-s both decrease with x. Noticeable magnetoresistance is only found for x < 0.3, being maximum around x = 0.05.

Magnetic and transport properties of Tl2Mn2−xRuxO7 pyrochlore are studied as a function of the Ru substitution rate x. The use of Ru4+ substitution in the Mn4+ network provides a convenient way to modify the charge density in the Tl–O band without disrupting it with foreign cations, a fact which allows to study the effects of the charge carriers density on the transport properties of the system. Magnetic mesurements indicate that in the low substitution rate (x⩽1) Ru 4d electrons have an itinerant character but for higher x they become localized leading to a strong reinforcement of antiferromagnetic interactions. Resistivity also changes drastically with x and noticeable magnetoresistance is only found for x<0.3. Indications in favor of activated behavior and charge carrier localization, suggesting the existence of spin polarons, are found above Tc.

Transport and structural properties of the colossal magnetoresistance pyrochlore TI 2 Mn 2 O 7 are studied as a function of applied pressure up to ~20GPa. This allows us to probe the effect of structural changes on the ferromagnetic transition and the transport properties. We observe a non-monotonous pressure dependence of the ferromagnetic transition temperature. We correlate this unusual variation with the structural parameters that, according to electronic band calculations, are key in controlling the properties of these materials.

Transport and structural properties of the colossal magnetoresistance pyrochlore TI2Mn2O7 are studied as a function of applied pressure up to ~20GPa. This allows us to probe the effect of structural changes on the ferromagnetic transition and the transport properties. We observe a non-monotonous pressure dependence of the ferromagnetic transition temperature. We correlate this unusual variation with the structural parameters that, according to electronic band calculations, are key in controlling the properties of these materials.

All AlN films deposited from 300 to 700°C on silica, Si(100) and Si(111) substrates exhibit (00.2) and (10.1) preferential orientations. We obtain the highest degree of preferential alignment of the (0001) planes of AlN on silica substrates reported to date for a deposition temperature of 350°C. In this ‘low’ temperature range, the multiple of random density values (mrd-values) have a low dependence on the nature and orientation of the substrates. At 700°C, we obtain a mrd-value of 165 on Si(111) with additionally a significant in plane orientation. As T increases in this ‘mean’ temperature range (>350°C), crystalline substrates, then the fit of the symmetry of the substrate surface with that of the growing film gives increasing mrd-values.

The magnetic and transport properties of Tl2Mn2−xRuxO7 pyrochlores are analyzed as a function of the substitution rate (0⩽x⩽2). For x⩽0.2, the system exhibits colossal magnetoresistance (CMR) and ferromagnetic ordering. For higher doping rates CMR is completely washed out and the transport properties mimics that of the Tl2Ru2O7 pure compound with a semiconductor-to-metal transition at a temperature that decreases as x increases. The magnetic frustration progressively increases signalling the increase of antiferromagnetic interactions and the geometrical frustration intrinsic to the pyrochlore structure.

The magnetotransport properties of the Tl2Mn2-xRuxO7 pyrochlore are studied. It is shown that Ru4+ substitution in the Mn4+ network provides a convenient way to modify the charge density in the Tl-O band without disrupting it with foreign cations. The experimental data reveal that the magnetoresistance has a quadratic dependence on the magnetization and increases when the charge density in the Tl-O conduction band is reduced. Above the Curie temperature, activated resistivity is found, signaling carrier localization and suggesting the existence of spin polarons. These results provide a solid support to recent theoretical predictions for magnetoresistance in low carrier density ferromagnets.

The crystallographic texture of the three main constituting phases of a granodioritic rock have been determined quantitatively, using neutron diffraction with a position sensitive detector. Intensities deconvoluted from the full profiles were used in the orientation distribution refinements using the WlMV algorithm. Satisfactory results were obtained for the three phases.

The magnetotransport properties of the ${\mathrm{Tl}}_{2}{\mathrm{Mn}}_{2\ensuremath{-}x}{\mathrm{Ru}}_{x}{\mathrm{O}}_{7}$ pyrochlore are studied. It is shown that ${\mathrm{Ru}}^{4+}$ substitution in the ${\mathrm{Mn}}^{4+}$ network provides a convenient way to modify the charge density in the Tl-O band without disrupting it with foreign cations. The experimental data reveal that the magnetoresistance has a quadratic dependence on the magnetization and increases when the charge density in the Tl-O conduction band is reduced. Above the Curie temperature, activated resistivity is found, signaling carrier localization and suggesting the existence of spin polarons. These results provide a solid support to recent theoretical predictions for magnetoresistance in low carrier density ferromagnets.

A single-line analysis of X-ray diffraction patterns was improved to study the microstructure of boron doped diamond films. This analysis requires that an analytic function be ascribed to each reflection. Such a function must model the observed data as precisely as possible and should allow readily a separation of the breadth of convoluted functions. The line profile due to size effect is assumed to be a Cauchy function and the shape of the strain profile is taken as a Gauss function.

We study the (004) diffraction peaks of (001) homoepitaxial diamond films (deposited by microwave plasma chemical vapor deposition) vs their boron content from 2×1017 to 8×1020 cm−3. The lattice parameter calculated for the relaxed films slightly increases according to the linear Vegard’s law up to 2.7×1020 [B] cm−3, then more rapidly with another linear law. We ascribed this second law to an additional electronic contribution from the hole on the boron impurity band with a positive deformation potential around 16 eV. There is overall agreement between the deduced in-plane stresses and the Raman peak positions. The full width at half maximum of the diffraction peak is dominated by the concentration of residual defects which are lower in the film than in the substrate up to 1020 [B] cm−3.

The (004) X-ray rocking curves of undoped and boron doped homoepitaxial diamond films have been recorded up to 8 × 1020 [B] cm−3. Up to this concentration the films grew coherently, i.e. the in-plane lattice constant of the doped film is the same as that of the substrate. The lattice constants of the boron doped diamond films in their relaxed state have been determined. Boron incorporation induces a large expansion of the lattice constants, especially above the semiconductor-metal transition. We suggest a contribution of both the different size of boron and carbon atoms (Vegard's law) and of hole concentration in the impurity band of boron [with a positive deformation potential of the impurity band of boron of 16 (± 0.3) eV] to describe the experimental results.

The X-ray diffraction peaks of undoped and boron-doped polycrystalline diamond films have been recorded up to 8 × 1020 B-cm−3. The lattice parameter varies slightly according to the crystallographic direction [111], [220] and [311] of the crystalline perpendicularly to the substrate. For undoped films, it is lower in the [220] direction. In all directions, we measure a large expansion coefficient of the diamond lattice versus the boron incorporation [B]. Microstrains appear independent of [B], while coherent domains have a maximum size around 3 × 1019 B cm−3. We suggest contribution of both the different of size of boron and carbon atoms (Vegard's law) and of holes in the impurity band of boron (but with a positive “deformation potential”) to describe the lattice expansion from boron incorporation.