Tailoring of thermodynamic behaviors and magnetocaloric properties in (GdTbDyHoErTm)CoAl metallic glasses based on high-entropy effects

<p indent="0mm">In this work, quinary (Gd_1/3Tb_1/3Ho_1/3)₅₅Co_17.5Al_27.5, senary (Gd_1/4Tb_1/4Dy_1/4Ho_1/4)₅₅Co_17.5Al_27.5, septenary (Gd_1/5Tb_1/5-Dy_1/5Ho_1/5Er_1/5)₅₅Co_17.5Al_27.5, and octonary (Gd_1/6Tb_1/6Dy_1/6Ho_1/6Er_1/6Tm_1/6)₅₅Co_17.5Al_27.5 high entropy (HE) metallic glasses (MGs) with critical diameters of more than <sc>5 mm</sc> were successfully designed and fabricated via RE element substitutions. Systematic investigations into their thermodynamic behaviors and magnetocaloric effects (MCE) were conducted. It suggests that high configurational entropy (Δ<italic>S</italic>_conf) might deteriorate glass forming ability (GFA) and simultaneously improve thermal stability. With increasing Δ<italic>S</italic>_conf from 1.593<italic>R</italic> to 1.974<italic>R</italic>, the thermodynamic parameters such as the glass transition temperature (<italic>T</italic>_g) and initial crystallization temperature (<italic>T</italic>_x) significantly increase from <sc>618</sc> to 653 K and <sc>684</sc> to <sc>708 K,</sc> respectively. Based on microstructural analysis, it is found that the significant ordered structure demonstrated in HE MGs severely reduces GFA. However, the Δ<italic>S</italic>_conf has a negligible impact on the magnetocaloric parameters such as the curie temperature (<italic>T</italic>_c), the maximum magnetic entropy change (<inline-formula id="INLINE57"><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:mrow><mml:mo stretchy="true">|</mml:mo><mml:mrow><mml:mi>∆</mml:mi><mml:msubsup other="0"><mml:mi other="0">S</mml:mi><mml:mi other="1">M</mml:mi><mml:mrow other="1"><mml:mtext other="1">pk</mml:mtext></mml:mrow></mml:msubsup></mml:mrow><mml:mo stretchy="true">|</mml:mo></mml:mrow></mml:mrow></mml:math></inline-formula>), and relative cooling power (RCP), while RE elements still play a major role on determining the magnetocaloric properties. Studies of MCE indicate that the distinguished spin glass behaviors and high degree of structural order in rare-earth-based HE MGs lead to an enhanced RCP and a broader magnetic-transition temperature range, whereas <italic>T</italic>_c and <inline-formula id="INLINE58"><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:mrow><mml:mo stretchy="true">|</mml:mo><mml:mrow><mml:mi>∆</mml:mi><mml:msubsup other="0"><mml:mi other="0">S</mml:mi><mml:mi other="1">M</mml:mi><mml:mrow other="1"><mml:mtext other="1">pk</mml:mtext></mml:mrow></mml:msubsup></mml:mrow><mml:mo stretchy="true">|</mml:mo></mml:mrow></mml:mrow></mml:math></inline-formula> more depend on the de Gennes factor rather than Δ<italic>S</italic>_conf. Our work shows that the quinary (Gd_1/3Tb_1/3Ho_1/3)₅₅Co_17.5Al_27.5 exhibits an excellent magnetocaloric effect with <inline-formula id="INLINE59"><mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:mrow><mml:mo stretchy="true">|</mml:mo><mml:mrow><mml:mi>∆</mml:mi><mml:msubsup other="0"><mml:mi other="0">S</mml:mi><mml:mi other="1">M</mml:mi><mml:mrow other="1"><mml:mtext other="1">pk</mml:mtext></mml:mrow></mml:msubsup></mml:mrow><mml:mo stretchy="true">|</mml:mo></mml:mrow></mml:mrow></mml:math></inline-formula> and RCP of <sc>8.82 J kg⁻¹ K⁻¹</sc> and <sc>559.27 J kg⁻¹</sc> under an applied field of <sc>5 T,</sc> respectively. In conclusion, we can design much more stable MCE MGs with a tunable <italic>T</italic>_c for different applications via entropy tailoring.