A two-dimensional Zakharov Kuznetsov (ZK) equation was derived for ion-acoustic (IA) solitons in magnetoplasmas with relativistic streaming warm ions, superthermal electrons and positrons, and stationary heavy ions (either positive or negative). The transverse instability of the IA solitons was investigated using the small- κ perturbation expansion method. The effects of plasma parameters such as the concentration of positive/negative heavy ions, relativistic streaming velocity of ions, superthermality of electrons and positrons, positron concentration, ion temperature, and magnetic field strength on the instability of IA solitons are investigated. These parameters have a significant effect on the instability growth rate. The results also indicate that the solitons tended to be stable in the plasma model containing negatively charged heavy ions. The findings of this work may provide valuable insights into the understanding of astrophysical systems, especially in the context of pulsar magnetospheres, solar wind, and Van Allen radiation belts, where relativistic ions and superthermal electron-positron coexist with heavy ions.
