Multiple Metamagnetic Transitions in the Magnetic Refrigerant $\mathrm{La}(\mathrm{Fe},\mathrm{Si}{)}_{13}{\mathrm{H}}_x$

The effect of hydrostatic pressure on thermally and field-induced first-order magnetic phase transitions is studied in the $\mathrm{La}(\mathrm{Fe},\mathrm{Si}{)}_{13}$-type compounds. A peculiar series of consecutive field-induced transitions is realized using a distinct combination of hydrostatic pressure and negative pressure created by the interstitial insertion of hydrogen. The pressure-induced discontinuous magnetization jumps result in an enhanced cooling power, thus opening up the possibility to exploit in full the magnetocaloric potential of this compound class.

Figure 1

The effect of applied hydrostatic pressure on the magnetization $M$ measured on cooling in an external magnetic field of 10 mT for (a) ${\mathrm{LaFe}}_{11.57}{\mathrm{Si}}_{1.43}$ and (b) ${\mathrm{LaFe}}_{11.57}{\mathrm{Si}}_{1.43}{\mathrm{H}}_{1.64}$. Inset: The magnetization in a magnetic field of 5 T.

Figure 2

Magnetization isotherms in the vicinity of the Curie temperature $T_c$ at various pressures for (a) ${\mathrm{LaFe}}_{11.57}{\mathrm{Si}}_{1.43}$ and (b) ${\mathrm{LaFe}}_{11.57}{\mathrm{Si}}_{1.43}{\mathrm{H}}_{1.64}$. Arrows indicate the direction of temperature and magnetic field change. Open triangles mark magnetization curves at $T_c$. $H_{mi}$ indicates the critical field for the $i$th metamagnetic transition.

Figure 3

Temperature dependence of the critical field $H_{mi}$ of the metamagnetic transitions at various pressures in ${\mathrm{LaFe}}_{11.57}{\mathrm{Si}}_{1.43}{\mathrm{H}}_{1.64}$. The dashed lines are linear fits of the experimental data.

Figure 4

Magnetic entropy change $\Delta S_M$ as a function of temperature and pressure in (a) ${\mathrm{LaFe}}_{11.57}{\mathrm{Si}}_{1.43}$ and (b) ${\mathrm{LaFe}}_{11.57}{\mathrm{Si}}_{1.43}{\mathrm{H}}_{1.64}$. Open and closed symbols correspond to $\Delta S_M$ for a field change of 2 and 5 T, respectively.