Evolution of Structural Transformation in γ′-Fe₄N and GeNFe₃

Abstract

Ge-substitution dependence of the structural, electronic, and magnetic properties for Ge x NFe 4−x (0.0 ≤ x ≤ 1.0) compounds has been investigated systematically. An obvious structural phase transition from Pm3m to I4/mcm around x = 0.5 is observed by substitution-dependent X-ray diffractions. The modified lattice constants a′ = a/2 1/2 and c′ = c/2 are used to depict the specific structure for tetragonal GeNFe 3 . Especially, the tetragonal structure exhibits an expansion along the direction of the c axis compared with the cubic γ′-Fe 4 N; also, the sublattice of the octahedral structure around N atoms is stretched along the tetragonal [001]. As a consequence of increasing substitution, lower ferromagnetic (FM) to paramagnetic transition temperature is associated with the tetragonal GeNFe 3 (T C ≈ 90 K). The much higher magnetization (M s ) of γ′-Fe 4 N than that of GeNFe 3 can be attributed to the FM and ferrimagnetic ground states, respectively, which are confirmed by the density functional theory calculations. The average magnetic moment for GeNFe 3 is about 0.446 μ B /atom per formula unit based on the calculations, which is approximately similar to the experimental value. Our calculations determine that the electrons of Fe-3d contribute the dominant role among the total density of states, and Ge-4p and N-2p are mainly contributed away from the Fermi energy (E F ).

Discovery of the Griffiths phase in the quaternary nitrides Ge1−xSnxNFe3

“…The diffraction patterns can be well satisfied by corresponding Pm 3 m and I 4/ mcm with reliable fitting parameters ( R p , R wp , and χ 2 ), indicating that our samples are good in quality. The refined lattice parameters ( a = 3.8949 Å for cubic SnNFe 3 ; a = 5.3052 Å, c = 7.7539 Å for tetragonal phase GeNFe 3 ) by using the standard Rietveld technique are quite agreement with other previous reports 14,15 …”

“…Now, we begin to discuss the observed structure transition; in reverse, the cubic structure (Pm3m) cannot support the shrinking lattice, and thus, tetragonal structure (I4/mcm) appears in Ge 1−x Sn x NFe 3 around the critical dopants x around the interval 0.4−0.5. 15 The insets of spatial diagram in Figure 2 give the detailed structural category for GeNFe 3 and SnNFe 3 , and this result is completely consistent with the developing progress of lattice characteristics. And likewise, this observed structural transition is similar to the previous investigation of GaCFe 3−x Co x , 17 which is also resulted from the collapsed structure.…”

“…The refined lattice parameters (a = 3.8949 Å for cubic SnNFe 3 ; a = 5.3052 Å, c = 7.7539 Å for tetragonal phase GeNFe 3 ) by using the standard Rietveld technique are quite agreement with other previous reports. 14,15 Figure 2 performs the modified lattice parameters aʹ, cʹ, and volume of unit cell Vʹ for all Ge 1−x Sn x NFe 3 (0 ≤ x ≤ 1) series of compounds. The criterion of the modification for lattice parameters adopts the theory aʹ = a (for cubic structure); aʹ = a/2 1/2 , cʹ = c/2 (for tetragonal structure).…”

“…All the obtained lattice parameters are listed in Table 1. Now, we begin to discuss the observed structure transition; in reverse, the cubic structure ( Pm 3 m ) cannot support the shrinking lattice, and thus, tetragonal structure ( I 4/ mcm ) appears in Ge 1− x Sn x NFe 3 around the critical dopants x around the interval 0.4−0.5 15 . The insets of spatial diagram in Figure 2 give the detailed structural category for GeNFe 3 and SnNFe 3 , and this result is completely consistent with the developing progress of lattice characteristics.…”

Violation of the Rule of Parsimony: Mixed Local Moment and Itinerant Fe Magnetism in Fe$_{3}$GeN

“…[14][15][16] Scholz and Dronskowski 17 found that the structure of Fe 4−x Ge x N y changes from a cubic antiperovskite structure to the distorted tetragonal structure with increasing content of Ge replacing Fe. Liu and coworkers showed that this transition is con-tinuous as a function of Ge content in Fe 4−x Ge x N. 18 In any case, Fe 3 GeN, which shows a net magnetic moment 0.2-0.3 µ B /Fe with sample dependence, has tetragonal symmetry at room temperature. 17,19 This structure has a doubled primitive unit cell containing two formula units, space group I4/mcm, number 140.…”