PURPOSE: To obtain an organic magnetic material useful as a magnetic component of a toner for electrostatic development or of a magnetic ink.

CONSTITUTION: A magnetic ink composed mainly of a magnetic material, a pigment and a vehicle, wherein the magnetic material comprises a feldazyl- substituted thiophene polymer of the formula. This ink is used to produce a magnetic toner for electrostatic development. In the formula, R1, R2, R3 and R4 may be the same or different and are each at least one of H, a lower or higher alkyl group, a lower or higher alkoxy group, a monocyclic or condensed polycyclic hydrocarbon group and a heterocyclic aromatic group; and (n) is 2 or greater.