Effect of N, C and B interstitials on the structural and magnetic properties of alloys with Cu$_3$Au-structure

Abstract

High-throughput density functional calculations are used to investigate the effect of interstitial B, C and N atoms on 21 alloys reported to crystallize in the cubic Cu3Au structure. It is shown that the interstitials can have a significant impact on the magneto-crystalline anisotropy energy (MAE), the thermodynamic stability and the magnetic ground state structure, making these alloys interesting for hard magnetic, magnetocaloric and other applications. For 29 alloy/interstitial combinations the formation of stable alloys with interstitial concentrations above 5% is expected. In Ni3Mn interstitial N induces a tetragonal distortion with substantial uniaxial MAE for realistic N concentrations. Mn3XNx (X=Rh, Ir, Pt and Sb) are identified as alloys with strong magneto-crystalline anisotropy. For Mn3Ir we find a strong enhancement of the MAE upon N alloying in the most stable collinear ferrimagnetic state as well as in the non-collinear magnetic ground state. Mn3Ir and Mn3IrN show also interesting topological transport properties. The effect of N concentration and strain on the magnetic properties are discussed. Further, the huge impact of N on the MAE of Mn3Ir and a possible impact of interstitial N on amorphous Mn3Ir, a material that is indispensable in today's data storage devices, are discussed at hand of the electronic structure. For Mn3Sb, non-collinear, ferrimagnetic and ferromagnetic states are very close in energy, making this material potentially interesting for magnetocaloric applications. For the investigated Mn alloys and competing phases, the determination of the magnetic ground state is essential for a reliable prediction of the phase stability. FIG. 2. Interstitial positions in the Cu3Au-structure: 1b, 3d and 8g (from left to right).

Designing of Magnetic MAB Phases for Energy Applications

“…65 This applies particularly to Mn-based compounds, as revealed by a recent work that the energy landscape of the convex hull is drastically changed after considering the magnetic ground state. 66 According to the literature, the 212-type Mn 2 AlB 2 is observed to display an AFM magnetic ground state with Néel temperature about 390 K, will be discussed in detail elsewhere. Nevertheless, the energy difference between the FM and AFM states is less than 20 meV per atom, hence the magnetic ground state has no strong impact on the thermodynamic stability for such compounds.…”

“…This can be attributed to the nano-laminated crystal structure, where the magnetic interaction between the local Mn-moments is relatively weak, in comparison to the strongly frustrated fcc-lattice from the Cu 3 Au lattice considered in Ref. 66 It is noted that systematic evaluation of the magnetic ground states is a challenge, hereafter we will focus on the physical properties of the FM states, which should be valid for most of the other compounds.…”