  Motivated by the recent Magnetospheric Multiscale (MMS) observations of
oblique electron acoustic waves, we addressed the generation mechanism of the
observed waves by utilizing the reductive perturbation technique. The nonlinear
Zakharov-Kuznetsov (ZK) equation is derived for collisionless, magnetised
plasma composed of cool inertial background electrons, the cool inertial
electron beam, hot inertialess suprathermal electrons represented by a
$\kappa$-distribution, and stationary ions. Moreover, the instability growth
rate is derived by using the small-k perturbation expansion method. Our
findings reveal that the structure of the electrostatic wave profile is
significantly influenced by the external magnetic field, the unperturbed hot,
cool, and electron beam densities, the obliquity angle, and the rate of
superthermality. Such parameters also affect the instability growth rate. This
study clarifies the characteristics of the oblique electron solitary waves that
may be responsible for changing the electron and ion distribution functions,
which alter the magnetic reconnection process. Moreover, increasing the growth
rate with the plasma parameters could be a source of anomalous resistivity that
enhances the rate of magnetic reconnection.
