<p>We study the dynamics of subsonic solitary waves taking place in a nonlinear model of an elastic electrically conductive micropolar medium interacting with an external magnetic field. First, we perform the stability analysis using the concept of the Evans function. As a result of linearization about the soliton solution an inhomogeneous scalar equation is obtained. This equation leads to a generalized spectral problem to be investigated with the help of the Evans function, which depends only on the spectral parameter. This function is analytic and may have zeroes in the right half of the complex plane of the spectral parameter. These zeroes coincide with the unstable eigenvalues of the mentioned generalized spectral problem. For the case under consideration there are two modes decreasing at spatial infinity and we need to adopt the previously developed external form approach to construct the Evans function. Our stability results are confirmed with the direct numerical calculations of the evolution of solitary waves in question.</p>