  Using detailed first principles calculations, we have found a new class of
stable organic molecular magnets based on zwitterionic molecules possessing
donor, $\pi$ bridge, and acceptor groups. These molecules are organic molecules
containing only C, H and N. The quantum mechanical nature of the magnetic
properties originates from the conjugated $\pi$ bridge (involving only p
electrons) where the exchange interactions between electron spin are relatively
strong and local and are independent of the length of the $\pi$ bridge,
enabling the easy construction of a molecular magnetic device with specified
length.
