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X-ray photoelectron spectroscopy and magnetism of Mn1−x Alx alloys

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Rednic V., Rednic L., Coldea M., Pop V., Neumann M., Pacurariu R., Tunyagi A.
Open Physics
|
2008
|
vol. 6
|
issue 3
434-439
EN
X-ray photoelectron spectroscopy (XPS), magnetization and magnetic susceptibility of Mn1−x Alx (x = 0.0, 0.2, 0.4, 0.5, 0.6, 0.7) alloys are reported. X-ray diffraction measurements showed that all investigated samples have the same crystallographic structure as the parent compound (AuCu3-structure type). The alloys are disordered for x ≤ 0.5, but become almost crystallographically ordered for higher Al concentration. This change in the crystallographic order is reflected both in the magnetization and Curie temperature values. The exchange interaction is ferromagnetic between the pairs of the near-neighbour Mn-Ni and Ni-Ni magnetic moments and antiferromagnetic for Mn-Mn pairs. The last one is present only in the disordered alloys, which leads to smaller values of the magnetization of these alloys in comparison with the ordered ones. The Mn magnetic moment has the fully ordered value of 3.2 μB in all investigated alloys. The decrease of the Ni magnetic moment as the Al concentration increases may be explained by the hybridization of the Ni 3d and Al 3sp states, which leads to a partial filling of the Ni 3d band. The magnetic susceptibility measurements pointed out the existence of spin fluctuations on Ni sites.
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Structural and magnetic characterisation of the perovskite oxides La0.7Ca0.3−x NaxMnO3

100%
Tozri A., Bejar M., Dhahri E., Hlil E.
Open Physics
|
2009
|
vol. 7
|
issue 1
89-95
EN
X-ray powder diffraction (XRD) and magnetic measurements were performed in order to investigate the effect of Na+ ion substitution for Ca2+ ions on the crystallographic structure, the character of magnetic ordering, and the effect of transition temperature in La0.7Ca0.3−x NaxMnO3 manganites series (0 ⩽ × ⩽ 0.2). All samples crystallise in an orthorhombic structure with the Pnma space group. We have found a strong dependence of structural and magnetic properties on the cation-size disorder parameter σ 2. The temperature dependence of magnetization of all samples obeys the Bloch T 3/2 law. The values of the spin wave constant at low temperature B increase with the increase of x and the Curie temperature decreases. It is concluded that the substitution of Ca by Na+ ions causes a decrease in total exchange integral Aof the samples.
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