Magnetic structure of Gd₅Si₂Ge₂and Gd₅Si₂Ge_1.9M_0.1(M = Ga, Cu)

Abstract

Powder x-ray diffraction patterns of the doped compounds Gd(5)Si(2)Ge(1.9)M(0.1) (M = Ga, Cu) show the same crystal structure, orthorhombic Gd(5)Si(4)-type, in the ferromagnetic and paramagnetic phases. This is different from Gd(5)Si(2)Ge(2), whose paramagnetic phase is monoclinic. The magnetic structure at low temperature, solved from diffraction experiments with hot neutrons, is the same in all the three compounds, collinear ferromagnetic with moments along the crystal b-axis, or F(y)F(By) according to Bertaut's notation. These results, combined with those of heat capacity and magnetocaloric effect, indicate, similarly to Gd(5)Si(4), a second-order, purely magnetic, transition in the doped compounds explaining the absence of hysteresis.

R5T4 Compounds

“…FM first-order transformation is sharper in the single crystal than in a polycrystalline sample. This result is in disagreement with the magnetic measurements of Leib et al (2002a) and the neutron diffraction study by Palacios et al (2010b). Essentially, these materials have uniaxial magnetic anisotropy, which agrees with nearly tetragonal crystal structure (a % c < <b).…”

“…Neutron diffraction determination of the magnetic structure of Gd 5 Si 2 Ge 2 and doped Gd 5 Si 2 Ge 1.9 M 0.1 (M ¼ Ga, Cu) compounds confirms the collinear ferromagnetic alignment of Gd magnetic moments along the b-axis below T C (Palacios et al, 2010b). The magnetic structure is independent of whether the magnetic ordering occurred via a first-order transition (Gd 5 Si 2 Ge 2 ) or a second-order transition (Gd 5 Si 2 Ge 1.9 Ga 0.1 ).…”

“…The investigations of the Yb-Si binary system (Palenzona et al, 2003) and Yb-Ge binary system (Pani and Palenzona, 2003) reveal the existence of the phases with R 5 T 4 stoichiometry; both compounds were reported to crystallize in the O(II) Sm 5 Ge 4 type of crystal structure. The investigations of the Yb-Si binary system (Palenzona et al, 2003) and Yb-Ge binary system (Pani and Palenzona, 2003) reveal the existence of the phases with R 5 T 4 stoichiometry; both compounds were reported to crystallize in the O(II) Sm 5 Ge 4 type of crystal structure.…”

“…The investigations of the Yb-Si binary system (Palenzona et al, 2003) and Yb-Ge binary system (Pani and Palenzona, 2003) reveal the existence of the phases with R 5 T 4 stoichiometry; both compounds were reported to crystallize in the O(II) Sm 5 Ge 4 type of crystal structure. According to Palenzona et al (2003) Yb 5 Si 4 forms by peritectic reaction from YbSi and liquid at approximately 1680 C. On the other hand, Yb 5 Ge 4 melts congruently at 1640 C and it has the highest melting temperature among all other Yb-Ge binary compounds (Pani and Palenzona, 2003). They also assigned Sm 5 Ge 4 as a structure prototype but noted that the coordination of some of the Si atoms is different from the typical Sm 5 Ge 4 coordination and similar to the Gd 5 Si 4 type of crystal structure.…”

Structural and magnetic transitions inGd5SixGe4−xRyan1, Cadogan2, Cranswick3 et al. 2010Phys. Rev. B

“…After we completed this work we became aware of an independent study of Gd 5 Si 2 Ge 2 using hot ͑ ϳ 0.5 Å͒ neutrons where the authors report finding ferromagnetic order below the monoclinic ͑M͒ → O͑I͒ structural transition in the much more Si-rich region of the Gd 5 Si x Ge 1−x phase diagram. 23 …”