We developed a new method of fabricating a divalent copper ion (Cu2+) modified DNA thin film on a glass substrate and studied its magnetic properties. We evaluated the coercive field (Hc), remanent magnetization (Mr), susceptibility (χ), and thermal variation of magnetization with varying Cu2+ concentrations [Cu2+] resulting in DNA thin films. Although thickness of the two dimensional DNA thin film with Cu2+ in dry state was extremely thin (0.6 nm), significant ferromagnetic signals were observed at room temperature. The DNA thin films with a [Cu2+] near 5 mM showed the distinct S-shape hysteresis with appreciable high Hc, Mr and χ at low field (≤600 Oe). These were primarily caused by the presence of small magnetic dipoles of Cu2+ coordination on the DNA molecule, through unpaired d electrons interacting with their nearest neighbors and the inter-exchange energy in the magnetic dipoles making other neighboring dipoles oriented in the same direction.
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