Abstract: A method of preparing magnetically conductive powders based on principle of liquid flow control in a cavitation line, where in a jet tube are evoked, during the rise of a cavitation cloud and implosion of cavitation bubbles with intensity up to ultrasound frequency 24 kHz, pulse shock waves acting on a surface of a substance whereby are released particles in dimensions in range of micrometer or nanometer units. Particles of the substance from a jet tube are carried away by liquid media into a header where they are captured via a magnetic element. A device includes a cavitation line that is equipped for capture of decavitated particles of the substance by at least one header along which is placed a magnetic element.