Crystal and thermodynamic properties of Tb2Ni2X, (X = Al, Ga)

The crystal and thermodynamic properties of Tb2Ni2X (X = Al, Ga) are reported through measurements of X-ray diffraction (XRD), magnetic susceptibility, chi(T), magnetization, M(mu 0H) and heat capacity, Cp(T). XRD pattern analysis confirms the orthorhombic W2CoB2-type structure with the space group of Immm. chi(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 chi(C-p) 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. C-p(T) data of the nonmagnetic counterparts Y2Ni2X (X = Al, Ga) are well described by the Debye model giving a Debye temperature, theta(D) = 236.9(4) K and 225.3(2) K for Al and Ga compounds, respectively. The low-temperature part of the 4f-magnetic contribution to the total heat capacity, C-4f(T) can be described by the antiferromagnetic spin-wave dispersion, giving an energy gap Delta(sw) = 47(3) K and 26(2) K for Al and Ga compounds, respectively. The 4f - magnetic entropy S-4f(T) for both compounds reaches the value of 2Rln(2) close to their respective T-N values.