Abstract
The influence of Co (Ni) and B co-doping on the structural, magnetic and magnetocaloric properties of (Mn,Fe)(P,Si) compounds is investigated by X-ray diffraction (XRD), differential scanning calorimetry, magnetic and direct temperature change measurements. It is found that Co (Ni) and B co-doping is an effective approach to tune both the Curie temperature and the thermal hysteresis of (Mn,Fe)(P,Si) materials without losing either the giant magnetocaloric effect or the positive effect of the B substitution on the mechanical stability. An increase in B concentration leads to a rapid decrease in thermal hysteresis, while an increase in the Co or Ni concentration hardly changes the thermal hysteresis of the (Mn,Fe)(P,Si) compounds. However, the Curie temperature decreases slowly as a function of the Co or Ni content, while it increases dramatically for increasing B concentration. Hence, the co-substitution of Fe and P by Co (Ni) and B, respectively, offers a new control parameter to adjust the Curie temperature and reduce the thermal hysteresis of the (Mn,Fe)(P,Si) materials.
Highlights
The magnetocaloric effect (MCE), which was first described in 1917 by Weiss and Piccard [1,2], corresponds to the change in temperature when a magnetic field is changed under adiabatic conditions or the change in entropy when the field is changed under isothermal conditions
From a thermodynamic point of view, the isothermal magnetic entropy change ∆Sm and the adiabatic temperature change ∆Tad are two characteristic parameters to evaluate the MCE of a magnetic material
All samples were found to crystallize in the hexagonal Fe2 P-type structure, indicating that the Co and B co-doping do not affect the Fe2 P phase formation
Summary
The magnetocaloric effect (MCE), which was first described in 1917 by Weiss and Piccard [1,2], corresponds to the change in temperature when a magnetic field is changed under adiabatic conditions or the change in entropy when the field is changed under isothermal conditions. From an application point of view, (Mn,Fe) (P,Si)-based materials need to have a very small hysteresis that should at least be smaller than their adiabatic temperature change (∆Tad ) and have a continuously tunable TC close to the working temperature, so that they can be used as a feasible magnetic refrigerant material. Since the discovery of the (Mn,Fe) (P,Si) system, much effort has been put into tuning the Curie temperature (TC ) and reducing the thermal hysteresis (∆Thys ) without losing the giant MCE by varying the Mn/Fe and/or P/Si ratio [24], by substituting Mn and Fe by other transition metal and rare earths [25] or by substituting P or Si by B [26,27].
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