The Giant Magnetoresistance (GMR) effect occurs in nanoscale multilayer stacks of ferromagnetic and non-magnetic metals. When adjacent ferromagnet layers are parallel, electrons with matching spin pass with low scattering (low resistance). When antiparallel, all electrons encounter high scattering in at least one layer — resistance rises dramatically.
R_↑ = R₀(1 − P) // majority channel
R_↓ = R₀(1 + P) // minority channel
R_P = 2·R_↑·R_↓/(R_↑+R_↓)
R_AP = (R_↑+R_↓)/2
GMR = (R_AP−R_P)/R_P
ω_L = γ·B (γ ≈ 1.76×10¹¹ rad/s/T)
GMR was discovered in 1988 independently by Albert Fert (France) and Peter Grünberg (Germany). They shared the 2007 Nobel Prize in Physics. The discovery enabled a 1000× increase in hard drive storage density within 15 years. Your smartphone likely contains several GMR sensors.
This simulation visualises giant magnetoresistance (GMR): the way electrical resistance through a ferromagnet–spacer–ferromagnet stack changes depending on whether the two magnetic layers point the same way or opposite ways. It follows the two-current model, in which spin-up and spin-down electrons form separate conduction channels with resistances R↑ = R₀(1 − P) and R↓ = R₀(1 + P), so a parallel alignment gives low total resistance and an antiparallel alignment gives high resistance. Small arrows on each layer also show electron spins undergoing Larmor precession around the applied field at ω_L = γB.
A ferromagnet/spacer/ferromagnet stack with a fixed pinned layer and a switchable free layer. Electrons carrying spin up or spin down flow through the stack and scatter more or less depending on alignment, while live bars for the parallel (R_P) and antiparallel (R_AP) resistances and the GMR ratio update in real time.
Drag Spin Polarisation P to change how strongly spin affects scattering, Field Strength B to speed up the Larmor precession shown on each layer, and Voltage V to change the applied bias. Click the free layer (bottom) or press Flip Layer to switch between parallel and antiparallel states, and use Pause, Reset or Info for more detail.
GMR was discovered independently in 1988 by Albert Fert and Peter Grünberg, who shared the 2007 Nobel Prize in Physics for it. Their finding let hard-disk read heads shrink dramatically, increasing storage density roughly a thousandfold within about fifteen years.
GMR is a quantum effect in which the electrical resistance of a ferromagnet/spacer/ferromagnet stack is much lower when the two magnetic layers are aligned parallel than when they are antiparallel. It was discovered in 1988 by Albert Fert and Peter Grünberg, work recognised with the 2007 Nobel Prize in Physics.
Spin-up and spin-down electrons are treated as two independent conduction channels, each with its own resistance depending on whether it is the majority or minority spin in a given ferromagnet. In the parallel state one channel stays low-resistance in both layers; in the antiparallel state every channel meets high resistance in at least one layer, raising the total.
P sets how strongly a layer's magnetisation favours one spin direction, controlling the gap between the majority resistance R↑ = R₀(1 − P) and minority resistance R↓ = R₀(1 + P). A higher P widens that gap, producing a bigger difference between the parallel and antiparallel resistances and hence a larger GMR ratio.
The pinned layer's magnetisation is held fixed, exchange-biased against an antiferromagnet in real devices, while the free layer can be switched by clicking it or pressing Flip Layer. Comparing the free layer's direction with the fixed pinned layer determines whether the stack sits in its low- or high-resistance state.
GMR read heads let hard-disk drives detect much weaker magnetic fields from recorded bits than earlier technologies, driving a huge jump in storage density through the 1990s and 2000s. The same physics underlies modern MRAM memory and a wide range of magnetic field sensors used today.