PURPOSE: To achieve a magnetic measurement by electronic paramagnetic resonance(EPR) by using a specified tetracyanodimethane(TCNQ) derivative.

CONSTITUTION: As regard to a using method of a TCNQ derivative as given by the formula in EPR, AH+ in the formula is a cation derived from a heterocyclic aromatic base which has at least three arromatic nucleuses and a single NH groups contained in at least one of the nucleuses. In the use for a EPR magnetic measurement, it is important that nitrogen atoms of the cation bond to hydrogen atoms. Possible replacement of the atoms can exist on the carbon atoms of the aromatic nucleuses. In this derivative, a large degree of crowding can be obtained by replacing quinolinium cation with the cation having at least three aromatic nucleuses. This leaves a flat structure of one molecule for making an expansion of a π electron cloud to reduce a hf output required to eventually maintain a resonance.