First-principles study of phase stability and magnetic properties of B2-phase AlCr, AlMn, AlFe, AlCo, and AlNi aluminides

Using <a:math xmlns:a="http://www.w3.org/1998/Math/MathML"> <a:mrow> <a:mi>a</a:mi> <a:mi>b</a:mi> </a:mrow> </a:math> <b:math xmlns:b="http://www.w3.org/1998/Math/MathML"> <b:mrow> <b:mi>i</b:mi> <b:mi>n</b:mi> <b:mi>i</b:mi> <b:mi>t</b:mi> <b:mi>i</b:mi> <b:mi>o</b:mi> </b:mrow> </b:math> density functional theory (DFT) calculations, we investigate the electronic structure, phase stability, and magnetic properties of equiatomic binary alloys between Al and <c:math xmlns:c="http://www.w3.org/1998/Math/MathML"> <c:mrow> <c:mn>3</c:mn> <c:mi>d</c:mi> </c:mrow> </c:math> magnetic transition elements (Cr, Mn, Fe, Co, and Ni). Thermodynamically, all five binary aluminides are more stable in the ordered B2 phase than in the disordered body-centered-cubic phase, and Co is found to be the strongest B2 forming element with Al. The AlCo and AlNi compounds with B2 structure are verified to be nonmagnetic, whereas AlFe turns out to be weakly magnetic, which is consistent with other DFT calculations employing similar exchange-correlation approximations. Magnetic simulations based on the Heisenberg Hamiltonian predict an antiferromagnetic ground state for the hypothetical B2 AlCr, which is also confirmed by direct DFT calculations. Doping AlCr with Co leads to an antiferromagnetic-to-ferromagnetic transition, where ferromagnetism is to a large extent attributed to Cr atoms. The phase stability and magnetic trends are explained using electronic structure arguments. The present findings contribute to a deeper understanding of the phase stability and magnetic properties of Al binary alloys, providing insights into the formation mechanisms of the B2 structure with <d:math xmlns:d="http://www.w3.org/1998/Math/MathML"> <d:mrow> <d:mn>3</d:mn> <d:mi>d</d:mi> </d:mrow> </d:math> magnetic transition metals.