Unpaired spin refers to a property of a single electron inhabiting an orbital shell by itself. A single unpaired electron is more volatile and easier to get to react in chemical processes.
Most electrons spin in pairs; with paired electrons, the spin is more stable and the electron is more likely to stay with the atom it is currently orbiting. But when an electron is unpaired, the electron is much more likely to jump to another atom with another unpaired electron, creating a chemical bond.
Electron spin is studied in radicals that form in solid materials because a radical generally produces an unpaired spin on the molecule an atom is removed from. Study of these radicals helps scientists understand how radiation damage occurs and the locations and mechanism of radiation damage on even complex molecules.
Unpaired electron spin is studied with external magnet fields; in addition, unpaired electron spin generates its own magnetic field, and can be used in the production of magnets. In an isolated electron spin, only two orientations are possible. When these spins are lined up in an orderly fashion in a substance, the combined forces make that substance into a magnet.
Web Resources On Unpaired Spin
Electron Spin Resonance
Unpaired Spin Density
Book Resources On Unpaired Spin
Spin Dynamics: Basics of Nuclear Magnetic Resonance by Malcolm H. Levitt
Nuclear Magnetic Resonance by P. J. Hore