Esmat Dastanpour

Using Density Functional Theory (DFT) calculations and Monte-Carlo (MC) simulations, we investigate the recently reported magnetic transition in B2 Al–Cr–Co alloys. The Cr sublattice is alloyed with different amounts of Co in the antiferromagnetic (AFM) B2 AlCr binary alloy and the resulting exchange interactions are analyzed within the Heisenberg Hamiltonian framework. DFT results reveal that at low Co concentrations the system favors the AFM order, while at high Co contents a transition to the ferromagnetic (FM) state is observed. Within the FM stability field, the Curie temperature (TC), obtained within the mean-field approximation, is below ∼160 K and decreases with Co concentration. The calculated exchange parameters evolve systematically with Co content, and the trends are consistent with the DFT total energies. The magnetic configurations obtained from MC simulations follow the DFT results at low Cr levels but predict a spin-glass behavior for alloys containing more than 40 at. % Co on Cr sublattice. These findings provide a fundamental understanding of how the chemistry-driven changes in exchange interactions affect magnetism in the B2 Al–Cr–Co alloys.

Using a b i n i t i o density functional theory (DFT) calculations, we investigate the electronic structure, phase stability, and magnetic properties of equiatomic binary alloys between Al and 3 d 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 3 d magnetic transition metals.

Recently, we reported an antiferromagnetic ground state for equiatomic Al-Cr in the B2 structure. Here, by a joint theoretical–experimental study, we investigate the effect of Co additions to the Al-Cr alloy with the aim to synthesize a ferromagnetic B2 phase. Al₅₀Cr₃₈Co₁₂ (at.%) is prepared by arc melting from high-purity raw materials and solidifies into a combination of a Co-enriched B2 phase, a Co-depleted BCC phase, and an Al₈Cr₅ intermetallic phase. The as-cast alloy is ferromagnetic with a Curie point of 260 K, primarily due to the presence of about 54% B2 phase. Subsequent annealing decreases the fraction of the B2 phase to 27% with depletion of Cr from 20.2 at.% to 16.1 at.%, which leads to a reduction in its ferromagnetic behavior. Calculations based on Density Functional Theory (DFT) predict a corresponding decrease in the total magnetic moment and Curie temperature of the B2 phase by annealing. The present findings highlight the roles of Cr and Co in facilitating the formation of a metastable ferromagnetic B2 phase in this alloy.

Using Density Functional Theory (DFT) calculations and Monte-Carlo (MC) simulations, we investigate the recently reported magnetic transition in B2 Al-Cr-Co alloys. The Cr sublattice is alloyed with different amounts of Co in the antiferromagnetic (AFM) B2 AlCr binary alloy and the resulting exchange interactions are analyzed within the Heisenberg Hamiltonian framework. DFT results reveal that at low Co concentrations the system favors the AFM order, while at high Co contents a transition to the ferromagnetic (FM) state is observed. Within the FM stability field, the Curie temperature (TC), obtained within the mean-field approximation, is below ~160 K and decreases with Co concentration. The calculated exchange parameters evolve systematically with Co content, and the trends are consistent with the DFT total energies. The magnetic configurations obtained from MC simulations follow the DFT results at low Cr levels but predict a spin-glass behavior for alloys containing more than 40 at.% Co on Cr sublattice. These findings provide a fundamental understanding of how the chemistry-driven changes in exchange interactions affect magnetism in the B2 Al-Cr-Co alloys.

To our knowledge, no magnetic B2 phase in the Al–Mn system of near-equiatomic compositions has been reported so far. Here, we investigate the structural and magnetic characteristics of Al₄₅Mn_41.8X_13.2 (X = Fe, Co or Ni) alloys. We demonstrate that adding 13.2 atomic percent magnetic 3d metal to AlMn stabilizes a ferromagnetic B2 structure, where Al and X occupy different sublattices. We employ density functional theory calculations and experimental characterizations to underscore the role of the late 3d metals for the phase stability of the quasi-ordered ternary systems. We show that these alloys possess large local magnetic moments primarily due to Mn atoms partitioned to the Al-free sublattice. The revealed magneto-chemical effect opens alternative routes for tailoring the magnetic properties of B2 intermetallic compounds for various magnetic applications.

Understanding the electronic, lattice, and magnetic contributions to the magnetocaloric effect in magnetic materials can help to elucidate and optimize their performance. In this work, the structural and magnetocaloric properties of Al–Mn–Ni alloy are experimentally determined and theoretically analyzed based on ab initio calculations. The dominating B2 phase associated with the Mn-rich sublattice is found to be responsible for the observed magnetocaloric properties. The magnetic entropy change, refrigerant capacity, and adiabatic temperature change are evaluated. Through the analysis of the data, we find that for the B2 phase, changing from ferromagnetic to paramagnetic configurations results in a pronounced elastic hardening despite the volume expansion. The decrease in lattice entropy is significant and contributes negatively to the magnetic and electronic entropy changes. Our work emphasizes the critical role of the lattice sector in the magnetocaloric effect, and provides an in-depth understanding of the individual entropy terms in magnetic solid solutions.

Multi-component alloys have received increasing interest for functional applications in recent years. Here, we explore the magnetocaloric response for Al–Cr–Mn–Co medium-entropy alloys by integrated theoretical and experimental methods. Under the guidance of thermodynamic and ab initio calculations, a dual-phase system with large magnetic moment, i.e., Al50Cr19Mn19Co12, is synthesized, and the structural and magnetocaloric properties are confirmed via characterization. The obtained results indicate that the selected alloy exhibits a co-continuous mixture of a disordered body-centered cubic and an ordered B2 phase. The ab initio and Monte Carlo calculations indicate that the presence of the ordered B2 phase is responsible for the substantial magnetocaloric effect. The magnetization measurements demonstrated that this alloy undergoes a second-order magnetic transition with the Curie temperature of ∼300 K. The magnetocaloric properties are examined using magnetic entropy change, refrigeration capacity, and adiabatic temperature change. The property-directed strategy explored here is intended to contribute to the study of potential multi-component alloys in magnetocaloric applications.

The present work investigates how the vanadium (V) content in a series of Al₅₀V _x (Cr_0.33Mn_0.33Co_0.33)_(50−x) (x = 12.5, 6.5, 3.5, and 0.5 at.%) high-entropy alloys affects the local magnetic moment and magnetic transition temperature as a step towards developing high-entropy functional materials for magnetic refrigeration. This has been achieved by carrying out experimental investigations on induction melted alloys and comparison to ab initio and thermodynamic calculations. Structural characterization by x-ray diffraction and scanning electron microscopy indicates a dual-phase microstructure containing a disordered body-centered cubic (BCC) phase and a B2 phase with long-range order, which significantly differ in the Co and V contents. Ab initio calculations demonstrate a weaker magnetization and lower magnetic transition temperature (T _C) of the BCC phase in comparison with the B2 phase. We find that lower V content increases the B2 phase fraction, the saturation magnetization, and the Curie point, in line with the calculations. This trend is primarily connected with the preferential partition of V in the BCC phase, which however hinders the theoretically predicted antiferromagnetic B2 phase stabilizing effect of V. On the other hand, the chemistry-dependent properties of the ferromagnetic B2 phase suggest that a careful tuning of the composition and phase fractions can open the way towards promising high-entropy magnetic materials.

We investigate the Al_xCr_0.2MnFe_0.5Co_0.3Ni_0.5 (0.3 ≤ x ≤ 0.7) high-entropy alloys by combining experimental and theoretical techniques. X-ray diffraction and magnetization measurements indicate that Al alters the crystal structure and the entropy change upon magnetization–demagnetization while keeping the Curie temperature almost unchanged. First-principles calculations of the vibrational, magnetic, electronic, and configurational entropies show that the leading entropy change is due to the magnetic and vibrational degrees of freedom. The presence of the body-centered-cubic phase, showing a sizable elastic softening upon magnetic transition, brings about the substantial magnetocaloric effect in this family of alloys.