The Magnetic and Crystal Structure of MnxGa (1.15 ≤ x ≤ 1.8) Alloys

Abstract

Neutron powder diffraction patterns measured above TC have been used to determine the location of the excess Mn in MnxGa (1.15 ≤ x ≤ 1.8). This information has then been used to constrain the fits to neutron powder diffraction patterns measured at ambient temperature and so determine unambiguously the Mn moments in this system. We find that Mn randomly occupies the two Ga sites (2a and 2b) in the I4/mmm structure and propose that it is more appropriate to use a simpler structure based on the P4/mmm space group with a reduced unit cell. In this structure the two Ga sites are formally equivalent (they occupy the 1a site while Mn occupies the 1d site). Our experimental observations are supported by DFT calculations. Below TC we find that the Mn(1d) moment is constant at 2.45(3) μ B, while Mn on the 1a site carries a slightly larger moment (~3 μ B) that is coupled antiparallel to the Mn(1d) moments, leading to the observed drop in magnetisation with increasing Mn content in MnxGa.

Compositional Dependence of Epitaxial L10‐MnxGa Magnetic Properties as Probed by 57Mn/Fe and 119In/Sn Emission Mössbauer Spectroscopy

“…Mn atoms contribute to the magnetism with , while Ga atoms contribute with a negligible atomic moment to the macroscopic magnetism. [ 11,39 ] However, in the off‐stoichiometric conditions, the Mn atoms reside in 2 e Wyckoff position while the exceeded Mn atoms tend to occupy the natural Ga 1 a and 1 c positions, which increases the AF coupling between neighboring Mn atoms, thus lowering the overall magnetism as the Mn content increases. [ 39,40 ] The magnetic moments of Mn atoms which occupy Ga positions are larger than and antiparallel (Mn) to those Mn in their natural positions (Mn).…”

“…[ 11,39 ] However, in the off‐stoichiometric conditions, the Mn atoms reside in 2 e Wyckoff position while the exceeded Mn atoms tend to occupy the natural Ga 1 a and 1 c positions, which increases the AF coupling between neighboring Mn atoms, thus lowering the overall magnetism as the Mn content increases. [ 39,40 ] The magnetic moments of Mn atoms which occupy Ga positions are larger than and antiparallel (Mn) to those Mn in their natural positions (Mn). [ 4,26,39 ] Thus, due to the different atomic environments of the Mn I and Mn II positions (see Figure 1a) in Mn x Ga samples, different isomer shift have been used for the two sextets.…”

“…Although the Sn daughter atoms do not possess intrinsic magnetic moment, the neighboring Mn ions can induce a transferred hyperfine field due to the polarization of nonlocalized s electrons of the 119 Sn nuclei by the d electrons around Mn ions. [ 33,39,40 ] Within this assumption, the data reported in Figure 7 can be interpreted by using a distribution of magnetically‐split sextets with an average hyperfine field values up to 35 T, which is a very large value as induced by the transfer mechanism from neighboring Mn lattice sites. The isomer shift value has been found to be = 1.8 and δ = 1.2 mm s −1 for Mn 0.8 Ga and Mn 1.4 Ga, respectively.…”

“…Although in the composition range studied in this work, Mn x Ga should crystallize in the L 1 0 phase, the off‐stoichiometry and chemical disorder often present in these samples allow the structure to be described by L 1 0 and D 0 22 phases. [ 11,39 ] As shown in Figure 1a, in the stoichiometric Mn 1 Ga compound, Mn and Ga atoms occupy the 1 d and 1 a Wyckoff positions, respectively. Mn atoms contribute to the magnetism with , while Ga atoms contribute with a negligible atomic moment to the macroscopic magnetism.…”

Structure and magnetic properties of L1-MnGa nanoparticles prepared using direct reactions between Mn nanoparticles and Ga

“…The bulk samples of L1 0 -MnGa phase with high saturation magnetization were usually prepared by melting the ingots followed by annealing and/or quenching process. 6,7 The growth and characterizations of the L1 0 -MnGa films have been extensively studied since the observation of the square perpendicular hysteresis of Mn x Ga (1.2<x<1.5) films in 1990s. 3,8,9 The L1 0 -MnGa microparticles with size in the range of 10-50 µm had been prepared by high energy ball milling and subsequent annealing.…”