  We obtained steady solutions of optically thin, single temperature,
magnetized black hole accretion disks assuming thermal bremsstrahlung cooling.
Based on the results of 3D MHD simulations of accretion disks, we assumed that
the magnetic fields inside the disk are turbulent and dominated by azimuthal
component. We decomposed magnetic fields into an azimuthally averaged mean
field and fluctuating fields. We also assumed that the azimuthally averaged
Maxwell stress is proportional to the total pressure. The radial advection rate
of the azimuthal magnetic flux $\dot \Phi$ is prescribed as being proportional
to $\varpi^{- \zeta}$, where $\varpi$ is the radial coordinate and $\zeta$ is a
parameter which parameterizes the radial variation of $\dot \Phi$. We found
that when accretion rate $\dot M$ exceeds the threshold for the onset of the
thermal instability, a magnetic pressure dominated new branch appears. Thus the
thermal equilibrium curve of optically thin disk has a 'Z'-shape in the plane
of surface density and temperature. This indicates that as the mass accretion
rate increases, a gas pressure dominated optically thin hot accretion disk
undergoes a transition to a magnetic pressure dominated, optically thin cool
disk. This disk corresponds to the X-ray hard, luminous disk in black hole
candidates observed during the transition from a low/hard state to a high/soft
state. We also obtained global steady transonic solutions containing such a
transition layer.
