Developing magnetofunctionality: Coupled structural and magnetic phase transition in AlFe2B2

• AlFe2B2 undergoes a first-order magnetostructural transformation near room temperature.
• The AlFe2B2 Curie transition is thermally hysteretic and magnetic field dependent.
• XRD reveals a volume-conserved change in the lattice constants of the AlFe2B2 unit cell.
• The latent heat of the magnetostructural transformation is determined as 4.4 J/g.
• Results emphasize strong coupling between the magnetic spins and the lattice of the system.

Understanding correlations between crystal structure and magnetism is key to tuning the response of magnetic materials systems that exhibit large functional effects in response to small excursions in magnetic field or strain. To this end, temperature-dependent structure-magnetic property correlations are reported in samples of AlFe2B2 with the orthorhombic AlMn2B2-type layered structure as it traverses a thermally-hysteretic first-order magnetic phase change at a transition temperature of Tt = 280 K. Temperature-dependent x-ray diffraction carried out in the temperature range 200 K ≤ T ≤ 298 K reveals that the a and b lattice parameters increase by 0.2% and 0.1% respectively upon heating, while the c lattice parameter decreases by 0.3%, providing a conserved unit cell volume through Tt. A very small volumetric thermal expansion coefficient 4.4 × 10−6/K is determined in this temperature range that is one order of magnitude smaller than that of aluminum and only slightly larger than that of Invar. The latent heat of transformation associated with this magnetostructural phase transformation is determined as 4.4 J/g, similar to that of other magnetostructural materials. Overall, these features confirm a first-order thermodynamic phase change in the AlFe2B2 system that emphasizes strong coupling between the magnetic spins and the lattice to support potential magnetofunctional applications for energy transformation and harvesting.

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