Density-of-States Engineering of the MAX Phase (V _0.2 Cr _0.8 ) ₂ GaC by <i>A</i> -Site Alloying with Germanium to Tune the Magnetic Susceptibility

MAX phases are a group of layered carbides and nitrides with the unique quality of combining typical metallic and ceramic properties in one compound. Years after the first report of magnetic MAX phase thin films, it is still difficult to synthesize long-range magnetic MAX phases in the bulk. Based on (V 0.2 Cr 0.8 ) 2 GaC, a Pauli paramagnet that almost matches the Stoner criterion, we engineer the density of states near the Fermi level of the compound by introducing a Ga/Ge-solid solution on the A -site. This hitherto unknown double-site solid solution (V 0.2 Cr 0.8 ) 2 (Ga 1– y Ge y )C is synthesized in bulk as a full compositional series with 0 ≤ y ≤ 1 ( y = 0, 0.20, 0.40, 0.50, 0.60, 0.80, 1) using solid-state synthesis methods. The hitherto unknown MAX phases are structurally characterized by high-resolution X-ray powder diffraction and scanning electron microscopy. Experimental magnetometry is complemented by calculations of the density of states via density functional theory using fixed-spin moment analysis and global exploration of various magnetic states with the genetic algorithm. These approaches consistently indicate that no ordered magnetic state is stabilized in the studied compositions. However, Ga/Ge mixing reduces the energy penalty for ordered magnetic configurations, suggesting that A -site tuning can move the system closer to magnetic instability.