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Direct magnetocaloric characterization and simulation of thermomagnetic cycles
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View: Figures


Image of FIG. 1.
FIG. 1.

Sketch of the measurement probe. Panel (a) Top feedthrough, clip assembly, and slide seal, panel (b) lower connector and vacuum chamber.

Image of FIG. 2.
FIG. 2.

(a) Adiabatic temperature-change probe, (b) Cernox bare chip glued on the supporting plate, (c) sketch of the adiabatic temperature-change probe with sample.

Image of FIG. 3.
FIG. 3.

Temporal evolution of the magnetic field and effective sweep rate for the two cases: (a) the electromagnet is turned on, (b) the pneumatic actuator places the sample in the high field region of the magnet.

Image of FIG. 4.
FIG. 4.

Drawing of the cryostat insert. This attachment allows to control the system temperature in the zero field region.

Image of FIG. 5.
FIG. 5.

Direct Δ measurement across the Curie temperature of a Gadolinium sample in μΔ = 1.65 T both switching the field on and off. (Inset) Superimposed magnetic field profile (white triangles) normalized on the maximum expected Δ and the temperature profile obtained taking into account the sensor heat capacity (red thin profile). Yellow circles are the raw data.

Image of FIG. 6.
FIG. 6.

Δ vs. magnetic field at 292 K. Our characterization (yellow circles) is compared with values shown in Ref. (■ symbol), Ref. (★ symbol), and Ref. (▲ symbol). (Inset) Demonstrates the linear dependence of the Δ curve.

Image of FIG. 7.
FIG. 7.

Δ vs. temperature for magnetic field change of μΔ = 1.65 T (triangles). This measurement is compared with in-field DSC performed on the same sample for a μΔ = 1.7 T field variation (purple line).

Image of FIG. 8.
FIG. 8.

Δ vs. gadolinium sample mass at 292 K for a magnetic field change μΔ = 1.7 T (circles). The expected Δ as deduced from Eq. (1) (red line).

Image of FIG. 9.
FIG. 9.

Relative vs. mass for Gadolinium (black) and NiCoMnGa Heusler (white). (Inset) Normalized Δ vs. sample/sensor heat capacity ratio. These curves describe the sensitivity of the Δ probe.

Image of FIG. 10.
FIG. 10.

Specific heat and MCE (in inset) as measured on a 30 mg piece NiCoMnGa Heusler alloy for μΔ = 1.7 T.

Image of FIG. 11.
FIG. 11.

Temperature dependence of entropy in μ = 0.17 T and μ = 1.65 T. The thermomagnetic cycle of Figure 12(b) is shown. (Inset) curves compared with data from Ref. .

Image of FIG. 12.
FIG. 12.

Thermomagnetic cycles derived from direct Δ characterization at different frequencies. Figures (a)–(c) show the Gadolinium magnetocaloric behavior for different and temperatures of the cycle. Figure (d) shows the system temperature relaxation for a controlled asymmetric background temperature.


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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Direct magnetocaloric characterization and simulation of thermomagnetic cycles