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The crystal and thermodynamic properties of Tb2Ni2X (X = Al, Ga) are reported through measurements of X-ray diffraction (XRD), magnetic susceptibility, χ(T ), magnetization, M(μ0H) and heat capacity, Cp(T ). XRD pattern analysis confirms the orthorhombic W2CoB2-type with the space group of Immm. χ(T ) at high temperature for both compounds follows the Curie–Weiss relationship giving an effective magnetic moment close to that expected for the trivalent Tb ion. The low-temperature χ(T )/Cp(T ) data indicate that both compounds order antiferromagnetically at TN = 41 K / 40.4 K and 41.5 K / 41.4 K for Al and Ga compounds, respectively. Cp(T ) data of the nonmagnetic counterparts Y2Ni2X (X = Al, Ga) are well described by the Debye model given a Debye temperature, θD = 236.9(4) K and 225.3(2) K for Al and Ga compounds, respectively. The low-temperature of the 4f-magnetic contribution to the total heat capacity, C4f (T ) data can be well approximated according to the antiferromagnetic spin–wave dispersion, giving an energy gap Δsw = 4.1(3) meV and 2.2(2) meV for Al and Ga compounds, respectively. The 4f – magnetic entropy S4f (T ) for both compounds reaches the values of 2Rln(2) close to their respective TN values.
