S. Miraglia

Nonmagnetic thin layers of Ni3N

From structural analysis by x-ray diffraction, Rutherford backscattering spectroscopy, and physical investigations (magnetization and resistance), reactive sputtering assisted by microwave multidipolar plasma appears to be a powerful means for tailoring the stoichiometry of transition metal nitrides. Reactive sputtered nitride Ni layers were elaborated while keeping the Ar partial pressure constant (∼1.5u2002μbar) and varying the N2 partial pressure in the 0.1–0.5u2002μbar range. A mixing of Ni2N and Ni3N and a single-phase Ni3N are stabilized in thin layers for high and low p(N2), respectively. For the first time, an optimization of the crystallization of Ni3N pure layers is obtained for intermediate p(N2) (0.23u2002μbar). Both nitrided phases Ni2N and Ni3N, elaborated with appropriate deposition parameters, do not present ferromagnetic behavior in contrast to experimental results in the literature. Theoretical results using the full-potential linearized augmented plane wave method confirm the nonferromagnetic behav...

Hydrogen absorption in R2Fe17 alloys (R=rare earth metals) thermodynamics, structural and magnetic properties

Abstract Hydrogen absorption effects in the R 2 Fe 17 series of alloys have been established from pressure-composition (pc) isotherms, crystal structure determination and magnetic measurements. If no plateau pressure has been observed in the (pc)-isotherms, such curves have been found to be dependent on the nature of the R element. The results agree with a progressive but successive filling of the octahedral 2R-4Fe and the tetrahedral 2R-2Fe sites. Most of the modifications observed in the magnetic properties can be correlated with changes in selected Fe-Fe distances.

Hydrogen in hard magnetic materials

Abstract The rare-earth/transition metal alloys exhibiting high permanent magnet properties are able to reversibly absorb significant amounts of hydrogen. This affects markedly the fundamental characteristics of such intermetallics, and can be used as a probe to understand better the basis of the magnetic interactions. In addition, structural, mechanical and chemical aspects of the hydrogenation process are used to improve the synthesis of appropriate powders for the magnet technologies.

About hydrogen insertion in ThMn12 type alloys

Abstract The absorption of hydrogen in ternary RFe 12− x M x (R=Y or rare earth, M=Ti, Mo) alloys has been investigated by neutron diffraction. These compounds crystallise in the tetragonal (I4/mmm) structure of ThMn 12 type. In this work we report structural and magnetic investigations undertaken by neutron diffraction for some hydrides with high hydrogen contents and we focus on the location of hydrogen in Ti and Mo containing materials. The effects of hydrogenation on the intrinsic properties such as enhancement of Curie temperature, lattice parameters, Fe moment as determined by neutron diffraction, magnetic and Mossbauer measurements, are discussed.