In 1988 Albert Fert and Peter Grünberg independently discovered that stacking ultra-thin alternating layers of a ferromagnet (like cobalt) and a non-magnetic metal (like copper) produces a resistance that depends dramatically on whether the magnetic layers point the same way or opposite ways. The effect — Giant Magnetoresistance (GMR) — won them the 2007 Nobel Prize in Physics and let engineers shrink hard-drive read heads enough to enable the gigabyte- and terabyte-capacity drives we use today.
Commercial GMR read heads reached hard drives by 1997, just nine years after the discovery — an unusually fast lab-to-product turnaround that let areal density keep climbing well past what older inductive heads could sense.
A 3D magnetic multilayer stack lets you sweep an external field and watch the layers' magnetizations swing from antiparallel to parallel, while electrons flowing through the stack show, in real time, how spin-dependent scattering turns that magnetic alignment into a measurable change in electrical resistance.
A two-current (Mott) resistor model computes separate spin-up and spin-down channel resistances from each layer's magnetization angle; the channels combine in parallel, so a mismatched majority-spin channel dominates and resistance spikes in the antiparallel state.
Drag the external field slider past the coupling threshold to flip the stack from antiparallel to parallel and watch the relative resistance readout fall. Adjust spacer thickness to change how much field it takes, or click auto-sweep to watch it switch continuously.
Fert and Grünberg's 1988 discovery of GMR reached commercial hard-drive read heads by 1997 and won the 2007 Nobel Prize in Physics — it remains one of the fastest lab-to-industry transitions in condensed-matter physics.