When Samuel Goudsmit and George Uhlenbeck proposed the concept of electron spin in 1925, who could have predicted that one day it would revolutionize information technology? In conventional electronics, charges are manipulated by electric fields while spins are ignored. Yet just a decade after Goudsmit and Uhlenbeck’s proposal, Nevill Mott set the stage for the development of spintronics, the control of the electrons’ spin degrees of freedom in devices, which has now emerged as one of the most dynamic fields in condensed-matter physics.

Specifically, Mott realized that spin could influence conduction. In ferromagnetic metals such as iron, nickel, and their alloys, neighboring electrons can lower their energy by aligning their spins. The effect is to split the band structure of the ferromagnet by an amount known as the exchange energy. This exchange splitting of the bands leads to more majority-spin electrons (spin-up, say) at the Fermi level than minority (spin-down)...

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