Heat flux measurements of Tb3M series (M=Co, Rh and Ru): Specific heat and magnetocaloric properties

We report on the magnetic properties and magnetocaloric effect (MCE) for the Tb3M series, with M=Co, Rh and Ru, obtained using a heat flux technique. The specific heat of Tb3Co and Tb3Rh are very similar, with a first order type transition occurring around 6K below the magnetic ordering temperature without any corresponding feature on the magnetization. The slightly enhanced electronic specific heat, the Debye temperature around 150K and the presence of the magnetic specific heat well above the ordering temperature are also characteristic of many other compounds of the R3M family (R=Rare Earth). The specific heat for Tb3Ru, however, presents two peaks at 37K and 74K. The magnetization shows that below the first peak the system presents an antiferromagnetic behavior and is paramagnetic above 74K. We obtained a magnetocaloric effect for M=Co and Rh, −∆S=12J/kgK, but for Tb3Ru it is less than 3J/kgK (μ0∆H=5T). We believe that the experimental results show that the MCE is directly related with the process of hybridization of the (R)5d-(M)d electrons that occurs in the R3M materials.