Mpupa, Zandile2025-10-132025-10-132025https://hdl.handle.net/10566/21084The research reported in this thesis presents a comprehensive investigation into the structural, magnetic, and thermodynamic properties of the ternary polycrystalline Tb2Ni2X (X = Al, Ga) compounds through measurements of X-ray diffraction (XRD), magnetic susceptibility, χ (T), magnetization, M (µ0H), and heat capacity, Cp(T). The compounds were synthesized using an arc-melting furnace, and the ingots were cut using a slow cutter to ensure the formation of high-quality samples for further analysis. XRD analysis confirms the orthorhombic W2CoB2-type structure with the space group Immm. χ(T) at high temperature for both compounds follows the Curie–Weiss relationship giving an effective magnetic moment values µef f = 10.172(1) µB and 10.520(4) µB for Tb2Ni2Al and Tb2Ni2Ga compounds, respectively, which are close to that expected for the trivalent Tb ion of 10.72 µB. Negative Weiss temperature, θp was obtained for both compounds as expected for AFM exchange interactions between the Tb moments. 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 the Al and Ga compounds, respectively. χ(T) data in field-cooled (FC) and zero-field-cooled (ZFC) modes showed bifurcation below TN . M(µ0H) of Al compound exhibits hysteresis below 3 T, indicating magnetic domain structures and coercivity effects, while M(µ0H) for the Ga compound exhibits metamagnetic behavior above 6 T, suggesting a field-induced transition from antiferromagnetic to ferromagnetic states. Cp(T) data of the nonmagnetic counterparts Tb2Ni2X (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 the 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, ∆sw = 47(3) K and 26(2) K 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 indicating a ground state doublet for these compounds.enTernary Polycrystalline Tb2Ni2XThermodynamic PropertiesX-Ray Diffraction (XRD)Magnetic SusceptibilityM (µ0h)Thesis