  The phase transition of hard-sphere Heisenberg and Neutral Hard spheres
mixture fluids has been investigated with the density functional theory in
mean-field approximation (MF). The matrix of second derivatives of the grand
canonical potential $\Omega$ with respect to the total density, concentration,
and the magnetization fluctuations has been investigated and diagonalized. The
zero of the smallest eigenvalue $\lambda_s$ signalizes the phase instability
and the related eigenvector $\textbf{x}_s$ characterizes this phase transition.
We find a Curie line where the order parameter is pure magnetization and a
mixed spinodal where the order parameter is a mixture of total density,
concentration, and magnetization. Although in the fixed total number density or
temperature sections the obtained spinodal diagrams are quite similar topology,
the predominant phase instabilities are considerable different by analyzing
$\textbf{x}_s$ in density-concentration-magnetization fluctuations space.
Furthermore the spinodal diagrams in the different fixed concentration are
topologically different.
