| Article ID | Journal | Published Year | Pages | File Type |
|---|---|---|---|---|
| 1627426 | Journal of Alloys and Compounds | 2006 | 7 Pages |
The effect of structural disorder and chemical inhomogeneities on magnetic properties of the γ′-phase of Ni3Al alloys has been studied in a wide temperature range on polycrystalline and single-crystalline stoichiometric as well as on off-stoichiometric samples, by temperature dependent measurements of magnetization and magnetic susceptibility, as well as elastic neutron scattering. A transition of the compounds into the truly paramagnetic state is observed at temperatures exceeding the corresponding Curie temperatures TC ≈ 48.0–50.2 K for nominally stoichiometric samples by about 150 K. An off-stoichiometric sample with composition Ni0.771Al0.229 displays two magnetic transitions with TC1 ≈ 87.0 K and a second magnetic transition at a higher temperature TC2 ≈ 250.0 K. A temperature dependent asymmetry of neutron scattering peaks has been observed below 300 K for the stoichiometric γ′-Ni3Al sample. It becomes approximately constant below 180 K down to 30 K and must be traced back to quasi-static magnetic correlations for temperatures far exceeding TC. For the off-stoichiometric sample, this asymmetry exists as well and may even persist for T > TC2. It is concluded that likely chemical fluctuations yield a two-phase mixture of (partially ordered) γ and γ′ regions in all of these samples, which are detectable by the large magnetic neutron scattering contribution of the γ-phase. Clustering of the γ-phase explains the smeared appearance of the magnetic susceptibility in a temperature range fare above the ordering temperatures, and the effects of applied magnetic fields by superparamagnetic contributions.
