A magnetic matrix for magnetic separation of particles in a material feed includes a plurality of grooved plates having first and second sides that both have an alternating series of teeth and grooves therealong, each grooved plate having an offset alignment in which teeth and grooves on a first side of a plate are laterally offset from teeth and grooves on a second side of the same plate. Also provided are methods of using magnetic matrices to separate magnetic ores, with the methods characterized by a negative correlation in which magnetic matrices constructed with grooved plates having larger pitches are used for the separation of ultrafine particles.