The invention relates to the identification of molecules using an apparatus which includes: a head module comprising: an electromagnetic write-head configured to magnetically excite the molecule to be identified with an alternating magnetic field; and a magneto-resistive read sensor for measuring a resonant response of the magnetically excited molecule to be identified. The apparatus also includes a processor coupled to the magneto-resistive sensor, the processor being configured to compare the resonant response to a table of known resonant responses to identify a chemical composition of the molecule to be identified.