A magnetic powder is provided composed of particles having a balanced shape and distribution, the particles having a small, uniform volume, making it possible to achieve improved density and reliability of a coating type magnetic recording medium. The water discharge device intermittently forms the large air bubble to change a flow speed of a jet flow. The cover sheet defines at least one low temperature portion formed from a material having low heat conductivity and at least one high temperature portion formed from a material having high heat conductivity. A first rotary drive for rotating said measuring head is comprised within the first and the second modules. According to the invention, the magnetic field in the region of the channel is an inhomogeneous magnetic field. Modulated converter output resistance controls Vout, limits Iout, or improves current sharing.