Structural, magnetic properties and magnetocaloric effect of Mn1.2Fe0.8P1 − xSixB0.03 compounds

• The Curie temperature increases monotonously from 176 K to 280 K with increasing Si concentration.
• The magnetic entropy change gets a maximum of 16.3 J kg−1 K−1 for a magnetic field change of 0–2T.
• The phase transition is changed from first-order to second-order with increasing of Si contents.

Structural, magnetic, and magnetocaloric properties of the Mn1.2Fe0.8P1 − xSixB0.03(x = 0.4, 0.5 and 0.55) phases have been investigated. The experimental results show that the critical behavior of the paramagnetic to ferromagnetic phase transition can be tuned through the P/Si ratio. An increase in the Si concentration not only raises the Curie temperature from 176 K to 280 K, but also changes the nature of the magnetic transition from the first order (for x = 0.4) to the second order (for x = 0.55) and, thereby, affects the magnetocaloric properties. The peak values of the thermal hysteresis and magnetic entropy change for a magnetic field change of 0–2T are 10 K, 4 K, 0.8 K and −16.3, −8.7, −5.6 J kg−1 K−1 for x = 0.4, 0.5, and 0.55, respectively. Mechanisms for the magnetic hysteresis loss and possibilities for the room-temperature magnetic refrigeration are discussed.

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