We have investigated the influence of the exchange interactions between Mn atoms on the magnetic properties and the magnetic phase transitions in all d-metal Heusler-type model, Mn2NiZ where Z is an early transition metal atom Ti, Sc, or V. We used the double-time temperature-dependent Green’s function technique within the random phase approximation. Mn2NiZ has the Hg2CuTi-type structure consisting of four interpenetrating face centered cubic sub-lattices. Mn2NiZ exhibits a ferrimagnetic order due to antiparallel alignment between the Mn atoms and a behavior with completely compensated ferrimagnetism at temperatures close to the critical temperature. In the case of no external magnetic field, N-type ferrimagnetic behavior of Neél is observed. When the system is subject to an external magnetic field, the magnetization curves as a function of temperature exhibit quite interesting behaviors, and one observes the first-order phase transitions where the magnetization jumps. Indeed, we observed the magnetization plateau in the field dependence of the total magnetization at low temperatures.