To obtain organic ferromagnetic material, which is stable for a long period even in air by realizing magnetism at ordinary temperature by the radical salt crystal expressed by a specified chemical structural formula.

Tetrafluoro-tetracyanoquinodimethane (TCNQF4) and lithium iodide are dissolved in acetonitrile and made to react with algon gas being flown in. The formed precipitate is filtered and dried, and Li+TCNQF4 is obtained. After this material is dissolved into water again, the material is added into aqueous solution containing tetramethyl ammonium chloride, and the crude refined material of (CH3)4H+.TCNQF4 is obtained. After filtering and drying, the blue refined crystal, which is obtained by recrystallizing acetonitrile/diethyl ether, and TCNQF4 are recrystallized from acetonitrile/ diethyl ether. Then, radical crystal salt {(CH3)4N+.TCNQF4}1/2 (TCNQF4) expressed by the formula is obtained. In this crystal, the magnetizing curve becomes the S shape at 25°C and in the magnetic field range of ±600Oe, and hysterisis is shown.