Magnetic properties of ThFexAl12x alloys

Abstract

The results of magnetic properties of ThFexAl12–x powder samples with iron concentration x = 4, 4.5 and 5, studied by means of X‐ray (XD) and neutron diffraction (ND) techniques as well as the Mössbauer spectroscopy with the monochromatic circularly polarised source (MCPMS), and magnetisation measurements using vibrating sample magnetometer (VSM) are presented. Unpolarized neutron diffraction pattern leaves no doubts that the modulated magnetic structure is observed in the tetragonal ThFe4Al8 compound. The interpretation of our neutron data requires the presence of non‐zero magnetic propagation vectors different from the nuclear one. ThFe4Al8 sample has double spiral structure with moments rotating in a plane perpendicular to the wave vector as well as to . Both of them are temperature independent in the range 1.5 K–70 K. The value of iron magnetic moment is close to 1 μB/Fe atom at 1.5 K.

Reconstruction of the Exchange Integrals Map of ScFe4Al8Magnetic Structure

“…In order to reconstruct the exchange integrals map reproducing the observed spin ordering, the atomic magnetic (424) moments, modulation vectors and phase transition temperature the incommensurate magnetic structure modulation vector components τ 1 = 0.13 were approximated by τ 1 = 2/15 related to commensurate magnetic supercell, while τ 2 = 0.18 were approximated by 9/50. The phase dierence ∆ϕ a between the nearest neighbours (nn) along a direction, attributable to antiferromagnetic couplings where α is a canting angle [4,5], implemented during calculations was as close as possible approximation of the experimental results [1]:…”

Structural and magnetic properties of Sc1.1Fe3.9Al8 alloy

“…0 [4,10]. The magnetic moments of iron in all Th, U and Sc compounds turn out to have the value close to 1 m B atom À 1 [3][4][5][6][7][8][9][10][11][12][13][14], while in the reference La, Ce and Y alloys the Fe moment value was claimed to be close to 2 m B at low temperature [1].…”

“…In the well-known compounds MFe 4 Al 8 with M¼La or Ce [1] and Th [11], despite empty 4f -or 5f -shell in lanthanide and actinide ions, respectively, double cone or double spiral structures were discovered. In the case of double cone systems as in LaFe 4 Al 8 the magnetic structure is described by the set of two modulation vectors, with q !…”

“…Absence of magnetic moment on M element excludes them from direct exchange interactions. Moreover, studies of MFe 4 Al 8 compounds have shown that the magnetic properties of this family of alloys are sensitive to changes in iron concentration as well as to the disorder in the lattice [9][10][11][12][13]. Such changes can be due to the weight losses during sample preparation, which causes a small change in its composition and may in addition promote the precipitation of extra phases.…”

“…Among all known ternary compounds with the general formula MFe 4 À d Al 8 + d the polycrystalline samples [1][2][3] as well as the single crystals [4][5][6][7] with composition dE 0 have attracted most attention. A number of alloys with dA( À2; 0.5) and M ¼U, Th, Sc, Y was studied as well [8][9][10][11].…”