High pressure study of magnetocaloric effect in Ho₃Co and Tb₃Co

The magnetocaloric effect of intermetallic compounds of Tb₃Co and Ho₃Co is studied under high pressures up to ∼1 GPa using pressure dependent dc magnetisation and specific heat measurements at ambient conditions. The magnetic entropy change (-ΔS_M) obtained from magnetisation data and adiabatic change in temperature (ΔT_ad) determined from zero-field specific heat and magnetisation data are found to be nearly identical within error limits with those deduced from purely field dependent specific heat experiments. With increasing hydrostatic pressure to ∼1 GPa, the -ΔS_Mand ΔT_ad, both show a significant enhancement of about 37% and 13%, respectively for 9 T field change in case of Tb₃Co. On the other hand, Ho₃Co exhibits a decrease of about 8% in both -ΔS_Mand ΔT_adwith increasing pressure. The refrigerant capacity (RC) also increases from 650 J kg^-1to 847 J kg^-1in the case of Tb₃Co and it goes down from 665 J kg^-1to 615 J kg^-1for Ho₃Co for an increase of pressure to 1 GPa. With increasing pressure, the peak widths of both -ΔS_Mand ΔT_adincrease in case of Tb₃Co, although the increase is more in -ΔS_M. However, such noticeable changes in peak widths with pressure were not observed in Ho₃Co. At ambient pressure, peak of -ΔS_M(-ΔSMpk) scales with(H/TN)2/3for both the compounds, consistent with the prediction of mean field theory (MFT) for second order magnetic transition. However, deviation from MFT was noticed at high pressures as-ΔSMpkwas found to scale with(H/TN)3/4instead of(H/TN)2/3for both the alloys. Further, normalised -ΔS_Mcurves for different ΔHand pressures collapse on a single universal curve in both the compounds thereby indicating that the second order magnetic transition persists even up to ∼1 GPa pressure.