Magnetic phase diagram of the semiordered alloysUFexAl12−x

Abstract

Single crystals of the ternary semiordered alloys UFe x Al 12Ϫx with xϭ3. 8, 4.0, 4.2, 4.5, 4.7, 5.0, 5.5, and 5.8, were prepared, and found to crystallize in the tetragonal ThMn 12 -type structure ͑space group I4/mmm͒. Studies of monocrystalline and polycrystalline samples of these materials, by ac susceptibility, magnetization, and 57 Fe Mössbauer spectroscopy, show two magnetic transitions in the range of 4.0ϽxՇ4.7, where only a single transition has been previously reported for polycrystalline materials. These measurements yield the magnetic phase diagram of this system, extending the magnetic structures of single crystal UFe 4 Al 8 , determined by ͑unpolarized and polarized͒ neutron diffraction, of polycrystalline UFe 5 Al 7 , determined elsewhere by neutron diffraction, and of single crystal UFe 5.8 Al 6.2 , determined by magnetization. The four magnetic regions, identified in the magnetic phase diagram, and their proposed magnetic structures, are discussed.

Comparative studies of the cage systems ThFe2Al10 and UFe2Al10

“…We established the same contributions for the paramagnetic isostructural U-based aluminide. The specific heat curves for both ternaries exhibit anomalies at low temperatures, indicating the presence of spin fluctuations in the [Fe 2 Al 10 ] sublattice due to the closeness of this system to the quantum critical state, as observed previously for YFe 2 Al 10 . The electronic properties of ThFe 2 Al 10 are typical of metals.…”

Structural and magnetic properties of UFe6Ga6

“…It is interesting to notice that all the iron-iron interatomic distances are very close to the sum of the metallic radii, pointing for the possibility of predominant Fe-Fe ferromagnetic interactions. This contrasts with the UFe 6 Al 6 compound, where the Fe(8f)-Fe(8f) distances, 2.507 Å [8], are below the sum of the metallic radii and lead to antiferromagnetic interactions opposing the predominant ferromagnetic Fe(8f)-Fe(8j) and Fe(8j)-Fe(8j) interactions [16]. On the contrary, the longer iron-iron distances on the 8k sites in UFe 6 Ga 6 may reinforce the ferromagnetic interactions, as already proposed for the 3-d magnetic properties in UFe x Al 12Kx [16] and other uranium ThMn 12 type compounds such as the UFe 10 X 2 (XZSi, Mo, Re) [17].…”

Lattice vibration of Ce1−xScxFe4Al8

“…In fact for RT 4 Al 8 the 8f sites are the majority sites for T atoms, but a small amount of sites are also for Al atoms [30,33]. In addition, the stoichiometry of RT 4 Al 8 exhibits the compositions different from 1:4:8 ratio even single crystals of these materials [8,34]. These may result in the deviation of the calculations from the experimental data.…”

“…According to the stabilized structure of CeFe 4 Al 8 obtained from the above calculation, the supercell (CeFe 4-Al 8 ) 250 is applied to evaluate the lattice parameters and cohesive energies for Ce 12x Sc x Fe 4 Al 8 . In the calculations, the model of Ce 12x Sc x Fe 4 Al 8 is constructed with Sc atoms substituting randomly for Ce at the 2a sites.…”

“…Recently, a considerable attention [5][6][7][8][9][10] has been paid to the rare earth compounds RFe 4 Al 8 , which have the same structure and exhibit interesting magnetic properties. Neutron diffraction [7,9], Mö ssbauer effect [12,13] and magnetic [5,11] measurements have confirmed a complex antiferromagnetic (AF) ordering.…”