The $(A,B){\mathrm{Fe}}_2$-type Laves phase system is widely studied for a magnetochemical phase diagram, negative thermal expansion, and magnetocaloric effect. In this work, we develop a phase field model to theoretically investigate microstructure evolution and magnetic phase transitions in $({\mathrm{Hf}}_{1-x}{\mathrm{Nb}}_x){\mathrm{Fe}}_2$ pseudobinary alloys. Our simulations successfully capture the complex magnetic phase transitions within the system, including ferromagnetic (FM)-to-paramagnetic, ferromagnetic-to-antiferromagnetic (AFM), and antiferromagnetic-to-paramagnetic phase transitions. The phase diagram is obtained by the simulated magnetization-temperature curves and a triple point is identified at approximately $x=0.152$ and $T=313\mathrm{K}$, which shows excellent agreement with experimental data. Microstructure simulations reveal that the FM state forms a cuboidal-like domain pattern, while the AFM state exhibits a single domain. Moreover, a study of strain effects on ${\mathrm{Hf}}_{0.8}{\mathrm{Nb}}_{0.2}{\mathrm{Fe}}_2$ reveals that compressive strain suppresses the ferromagnetic state, and the FM-AFM phase transition temperature decreases by approximately 27 K per 0.1% increase in compressive strain, which is in accordance with experimental observations. This work provides theoretical insights into the magnetoelastic coupling in Laves phase alloys.

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• Domain walls
• Magnetic domains
• Magnetic phase transitions
• Alloys
• Intermetallic compounds
• Laves phases
• Phase-field modeling
• Time-dependent Ginzburg-Landau theory