Magnetic and Magnetocaloric Properties of Y(Co$_{1-x}$Fe$_x$)$_2$ ($x$ = 0.12–0.20) and Lu(Co$_{0.84}$Fe$_{0.16}$)$_2$ Compounds

To clarify the nature of the anomalously high magnetocaloric effect at low temperatures in the $RMe_2$ Laves type phases with “non-magnetic” rare-earth ions ($R$ = Y or Lu) and 3d elements of the Fe group ($Me$ = Fe, Co), the Y(Co$_{1-x}$Fe$_x$)$_2$ ($x$ = 0.12–0.20) and Lu(Co$_{0.84}$Fe$_{0.16}$)$_2$ compositions have been synthesized and their magnetic and magnetocaloric properties were investigated (isothermal magnetic entropy change $\Delta S_m$ and adiabatic temperature change $\Delta T_{\mathrm{ad}}$). It has been established that the iron concentration increases and/or Y by Lu replacement with unchanged Co : Fe ratio gives rise in the energy of the $d$–$d$ exchange interaction, which is followed by an increase in the Curie temperature value as well as by the low-temperature anomaly shift on the $\Delta S_m(T)$ dependence to a higher temperatures range.