Magnetoelastic and pressure effects at the antiferro–ferromagnetic transition in Hf1−xTaxFe2−y alloys

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Magnetostriction measurements using high-pulsed magnetic fields up to 14 T and thermal expansion measurements under hydrostatic pressure up to 12 kbar have been performed in Hf1−xTaxFe2−y alloys with x=0.17 and 0.15 and y=0.02. These compounds have a first-order magnetic phase transition from an antiferromagnetic (AF) high-temperature state to a ferromagnetic (F) low-temperature state at TAF–F=246 and 290 K, respectively. This transition is accompanied by a volume expansion from the low-volume AF state to the high-volume F state of ΔV/V≊0.56% and 0.38% for x=0.17 and 0.15, respectively. Hydrostatic pressure decreases significantly the AF–F transition temperature, whereas the thermal expansion anomaly becomes more pronounced. The dependence of TAF–F on pressure follows a quadratic behavior and TAF–F reaches a value of 106 K at 10.5 kbar for x=0.17. In search of high magnetostrictive materials, we have found a giant volume magnetostriction value (e.g., ω≊0.7% for the x=0.17 compound) in these alloys at a moderate applied magnetic field within the AF phase near room temperature, making these alloys potential candidates for magnetostrictive transducers.