 Tunnel magnetoresistance

Tunnel magnetoresistance is the change in resistance of a magnetic tunnel junction when the relative magnetizations of its two electrodes change. A common convention iswhere P and AP denote parallel and antiparallel alignment. This connects quantum tunnelling to the spin dependence of electronic states in the electrodes.

In the Jullière model, assume spin-conserving tunnelling with spin-independent matrix factors, and let the density of states polarizations at the Fermi energy be $P_i=(n_{i\uparrow }-n_{i\downarrow })/(n_{i\uparrow }+n_{i\downarrow })$. Parallel alignment pairs matching spin channels, while antiparallel alignment pairs opposite channels. Hence $G_{\mathrm{P}}\propto 1+P_1{P}_2$ and $G_{\mathrm{AP}}\propto 1-P_1{P}_2$. Using $R=1/G$ givesThis is a consequence of the stated two-channel model, rather than a universal material law.

M. Jullière's 1975 experiment compared the conductance of iron–germanium–cobalt thin-film junctions with parallel and antiparallel magnetizations at low temperature. The thin separating layer, magnetic preparation of the films and conductance measurement together made relative magnetic orientation an experimentally controllable transport variable.^[ref]

Tunnel magnetoresistance (TMR) is a quantum mechanical phenomenon observed in magnetic tunnel junctions (MTJs). These junctions consist of two ferromagnetic layers separated by a thin insulating barrier, typically only a few nanometers thick. TMR arises from the spin-dependent tunneling of electrons through this barrier.