Influence of sample geometry on determination of magnetocaloric effect for Gd60Co30Al10 glassy ribbons using direct and indirect methods

• Published in: Journal of magnetism and magnetic materials Vol. 323; no. 13; pp. 1782 - 1786
• Main Authors: Schwarz, B., Mattern, N., Moore, J.D., Skokov, K.P., Gutfleisch, O., Eckert, J.
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 01.07.2011; Elsevier
• Subjects: Condensed matter: electronic structure, electrical, magnetic, and optical properties; Exact sciences and technology; Magnetic cooling; Magnetic phase boundaries (including magnetic transitions, metamagnetism, etc.); Magnetic phase transition; Magnetic properties and materials; Magnetically ordered materials: other intrinsic properties; Magnetocaloric effect; Magnetocaloric effect, magnetic cooling; Physics; Magnetocaloric effect; Magnetic cooling; Magnetic phase transition; Gadolinium base alloys; Cooling rate; Magnetic field effects; Melt spinning; Magnetic transitions; Magnetic refrigerators; Specific heat; Metallic glasses; Aluminium alloys; Magnetocaloric effects; Temperature effects; Flow planar casting; Ferromagnetic-paramagnetic transitions; Cobalt alloys; Saturation magnetization; Transition element alloys
• ISSN: 0304-8853
• DOI: 10.1016/j.jmmm.2011.02.004

Rare-earth based metallic glasses with high saturation magnetization show a sizeable magnetocaloric effect (MCE) and are subject of extensive research concerning magnetic refrigeration materials. In this work, the magnetic phase transition from paramagnetic to ferromagnetic of Gd60Co30Al10 metallic glass has been characterized and three different methods were applied for the determination of its magnetocaloric specific parameters: (a) direct measurement of the adiabatic temperature change by exposing the material to an adiabatically applied magnetic field; (b) determination of the magnetization M(H,T) and calculation of the temperature dependent magnetic field induced entropy change ΔSm by application of the Maxwell relation and (c) measuring the total heat capacity Cp(H,T) in zero and non-zero magnetic field. Gd60Co30Al10 glassy ribbons were prepared by melt spinning, a technique that offers very high cooling rates due to the low dimensionality of the sample. Depending on the particular method of measurement, pieces of these glassy ribbons form samples with different appropriate total volume and dimensions. We show that the combination of the pronounced two-dimensionality of the ribbon pieces (aspect ratio ∼100) together with the very high magnetic permeability principally can cause strong internal demagnetizing fields that cannot be neglected when evaluating the intrinsic MCE parameters obtained from different methods. ► Direct measurement of the adiabatic temperature change. ► Magnetic field induced entropy change by application of the Maxwell relation. ► Measuring the total heat capacity Cp(H,T) in zero and non-zero magnetic field. ► Two-dimensionality of the ribbon pieces causes strong internal demagnetizing fields. ► Important when evaluating the intrinsic MCE parameters from different methods.