M. Ellouze

Neutron diffraction, NMR and magneto-transport properties in the Pr0.6Sr0.4MnO3 perovskite manganite

Abstract A Pr0.6Sr0.4MnO3 powder was synthesized by the solid state reaction method at 1400°C. Magnetic measurements show that our sample exhibits a paramagnetic–ferromagnetic transition with decreasing temperature. The paramagnetic to ferromagnetic transition is followed by a decrease of the magnetization below 100 K. The Curie temperature TC is found to be 310 K. Electrical studies show a semiconductor–metallic transition at Tρ=260 K. Our sample displays a magnetoresistance effect in 8 T of about 45% below 250 K. Neutron diffraction studies show that our sample crystallizes in the orthorhrombic system with Pnma space group at room temperature and at 200 K. However, at 10 K, we observe the coexistence of two phases: an orthorhombic phase with Pnma space group (27%) and a monoclinic one with 12/a space group (73%). 55Mn NMR measurements at 4.2 confirm the metallic behavior at low temperature. The observed frequency of 380 MHz is close to the calculated frequency of 378 MHz, which confirms the average value of Mn4+ and Mn3+ resonance frequencies.

The effect of substitution of Sm for Nd on the structure and magnetic properties of Nd2Fe17

Abstract The influence of Sm substitution in Nd 2− x Sm x Fe 17 compounds ( x =0, 0.5, 1.0, 1.5, 2.0) on structural and magnetic properties has been investigated. X-ray diffraction analysis shows that they are single phase with Th 2 Zn 17 -type structure. The lattice parameters of the Nd 2− x Sm x Fe 17 compounds decrease with increasing x for x ⩽2. The Curie temperature increases with increasing Sm substitution. The room-temperature saturation magnetization decreases from 28.5 to 25.32xa0 μ B /mole.

Neutron diffraction and Mössbauer spectral study of Nd2Fe16Ti and its nitride

The 295 K powder neutron diffraction patterns and the temperature dependence of the Mossbauer spectra of Nd2Fe17−xTix and Nd2Fe17−xTixNy have been measured. A Rietveld refinement of the neutron diffraction patterns yields the Nd2Fe16.32Ti0.68 and Nd2Fe16.32Ti0.68N2.7 stoichiometries for the two compounds and indicates that titanium occupies only the 6c crystallographic site and nitrogen only the 9e site in the rhombohedral Th2Zn17 structure. The insertion of interstitial nitrogen into Nd2Fe16.32Ti0.68 produces a 6.8% increase in the unit cell volume. The relative areas of the Mossbauer spectral components indicate that iron–iron, iron–titanium, and titanium–titanium 6c–6c dumbbell pairs exist in both of these materials. The magnetic hyperfine fields observed for the iron on the 6c site in the iron–titanium dumbbell pair in both compounds is substantially reduced from that found in Nd2Fe17 and Nd2Fe17N2.6 because of the titanium dumbbell near neighbor. For all the remaining hyperfine parameters there is a ...

Structure, magnetic and electrical properties in the praseodymium deficient Pr0.8−x□xSr0.2MnO3 manganites oxides

Abstract Structural, magnetic and electrical properties of Pr deficient Pr 0.8− x □ x Sr 0.2 MnO 3 (0≤ x ≤0.2) samples have been investigated. Powder X-ray diffraction patterns are indexed in the orthorhombic perovskite system with Pnma space group. The unit cell volume decreases with increasing vacancy contents. The investigated samples exhibit a ferromagnetic to paramagnetic transition with increasing temperature. The highest obtained value of the Curie temperature is about 190 K. The presence of vacancies in structure increases the Curie temperature. At low vacancy concentrations a semiconductor like behaviour was observed. However, for x ≥0.15, the samples exhibit a semiconducting to metallic transition with decreasing temperature.

The effect of nitrogen insertion in the Nd2-xGdxFe17Ny gadolinium substituted compounds

Abstract The structural and magnetic properties of Nd 2− x Gd x Fe 17 N y ( x =0–2 and y ≈3) gadolinium substituted compounds were studied. X-Ray diffraction characterization showed that all our samples are single phase and crystallize in the rhombohedral Th 2 Zn 17 -type structure. Nitrogen insertion in Nd 2− x Gd x Fe 17 samples induced an increase in the unit-cell volume. This increase was found to be about 5.6% for all gadolinium contents. Magnetization measurements showed that nitrogen insertion induced a strong increase in the Curie temperature, Δ T c = T cy − T c0 , which depends on the gadolinium content. The values of Δ T c decrease with increasing gadolinium concentration. It was found to decrease from 125% for x =0 to 70% for x =2. Nitrogen insertion leads to an increase in the saturated magnetization, μ s ( y )− μ s (0)/ μ s (0), which increases with increasing gadolinium content. It was found to increase from 26% for x =0 to 53% for x =2. The volume effects on the Curie temperature of our samples have been studied. The evolution of Gruneisen parameter defined by Γ versus gadolinium contents was linear.

A comparative study of the physical properties of Pr0.5−x□xSr0.5MnO3 and Pr0.5Sr0.5−x□xMnO3 manganites

The effects of praseodymium or strontium deficient on the structural, magnetic and electrical properties of non-stoichiometric Pr 0.5-x □ x Sr 0.5 MnO 3 (0≤x≤0.16) and Pr 0.5 Sr 0.5-x □ x MnO 3 (0≤x≤0.25) manganese oxides have been investigated. Powder samples of Pr 0.5 Sr 0.5-x □ x MnO 3 (0≤x≤0.25) and Pr 0.5-x □ x Sr 0.5 MnO 3 (0≤x≤0.16) have been elaborated using the conventional solid state reaction technique. Our synthesized samples crystallize in the orthorhombic perovskite structure with Imma space group. With decreasing temperature, magnetic measurements show that all strontium-deficient samples exhibit a paramagnetic to ferromagnetic transition, however the praseodymium-deficient samples do not exhibit such transition. The Curie temperature T C evolution versus x in Pr 0.5 Sr 0.5-x □ x MnO 3 exhibits a parabolic behavior with a maximum of 325 K at about x =0.15. Pr 0.5 Sr 0.5-x □ x MnO 3 are metallic-like at low temperatures and semiconductor-like at high temperatures, however, Pr 0.5-x □ x Sr 0.5 MnO 3 samples are semiconductor in the whole temperature range 77-300 K.

New method of insertion of hydrogen in R2Fe16Ti alloys with RY and Nd

Abstract A new method of inserting hydrogen in R 2 Fe 16 Ti compounds with Rue605Y and Nd was employed with success. The insertion of hydrogen in the structure increases the lattice parameters and, in turn, the unit cell volume. The changes in lattice constants are in good agreement with those obtained by the classic hydrogenation method. The Curie temperature as well as the saturation magnetization increase after insertion of hydrogen.

Crystal and magnetic structure of Pr/sub 0.7/Sr/sub 0.3-x/MnO/sub 3/ (0/spl les/x/spl les/0.2) compounds

The electronic and magnetic properties of the ABO/sub 3/ type manganites (A=rare earth, B=Mn) depend sensitively on the ratio of divalent and trivalent atoms on the A sublattice. The substitution of rare-earth by Ca or Sr not only affects the total valence, but also the lattice spacing, which, in turn may affect the structure and magnetic ordering temperature. If these compounds are synthesized with less than stoichiometric amounts of the A site constituents, (relative to the Mn content), three possible outcomes may be considered: (a) single phase materials with vacancies on the A sublattice may be formed, (b) two phase materials with stoichiometric manganites and Mn/sub 3/O/sub 4/ may result, or (c) some combination of A and B may occur. We have carried out neutron diffraction (ND) studies on samples of Pr/sub 0.7/Sr/sub 0.3-x/MnO/sub 3/ with nominal x=0.0, 0.1 and 0.2, at 300 K and 10 K. The ND data clearly show the presence of Mn/sub 3/O/sub 4/ as a second phase in samples with x=0.1 and 0.2. Refinements of the manganite structure, based on the assumption that the ratio of Pr to Sr on the A site is equal to the nominal concentration, reveal that vacancies can be induced on the A site. In the x=0.2 sample, about 5.5% of the A sites are found to be vacant. The refined Mn moments in the z=0.0 and 0.1 samples at 10 K are found to be nearly equal (3.4 /spl mu//sub B/). The Pr moments are parallel to the Mn moments With magnitude of 0.27 /spl mu//sub B/ and 0.33 /spl mu//sub B/, respectively, in these two samples. The magnetic structure of x=0.2 sample is more complex due to the presence of an antiferromagnetic component.

Neutron diffraction, structural and magnetic properties of (La1-yPry)0.9Na0.1MnO3

Abstract A systematic study of the structural and magnetic properties of the diluted perovskite manganite oxides (La 1− y Pr y ) 0.9 Na 0.1 MnO 3 (0.2≤ y ≤0.8) had been carried on. In this study, the average ionic radius 〈 r A 〉 of the A cation site was systematically varied while keeping fixed the carrier concentration (Mn 3+ /Mn 4+ ratio). X-Ray diffraction investigations showed a structural transition from the rhombohedral to the orthorhombic system for 0.33≤ y ≤0.5. The unit cell volume decreases with increasing Pr 3+ content. Magnetic measurements showed that our synthesized samples exhibit a paramagnetic to ferromagnetic transition with decreasing temperature. Neutron diffraction studies show that (La 0.2 Pr 0.8 ) 0.9 Na 0.1 MnO 3 powder sample crystallizes in the orthorhombic system with Pnma space group at room temperature and at 10 K. The magnetic moment of Pr and Mn atoms are coupled parallel to the b -axis.

PRESSURE INDUCED REVERSAL OF THE VOLUME EXPANSION CAUSED BY INTERSTITIAL NITROGEN IN ND2FE17N3

Crystallographic properties of Nd2Fe17N3 have been investigated using powder neutron diffraction techniques at pressures up to 7.3 GPa. With increasing pressure, the unit cell volume of Nd2Fe17N3 decreases almost linearly at a rate of 6.1 A3/GPa without undergoing a phase transformation or expelling the interstitial nitrogen atoms. The observed rate of contraction corresponds to a bulk modulus of 1.4×1011u2009N/m2 for Nd2Fe17N3. The unit cell volume of Nd2Fe17N3 at 7.3 GPa is approximately equal to that of Nd2Fe17 at atmospheric pressure. Even though the unit cell of Nd2Fe17 expands anisotropically due to nitrogenation, contraction of the Nd2Fe17N3 unit cell under pressure appears to be isotropic with lattice parameters a and c decreasing by approximately 1.8% as the sample pressure increases from ambient to 7.3 GPa.