Spin valve
![A schematic diagram of a pseudo spin valve. The free layer is magnetically soft and the fixed layer is magnetically hard. When the magnetic layers are antiparallel the electrical resistance is higher than when they are aligned.](/Images/godic/202502/12/Spin_valve_schematic.svg2019.png")
A spin valve is a device, consisting of two or more conducting magnetic materials, whose electrical resistance can change between two values depending on the relative alignment of the magnetisation in the layers. The resistance change is a result of the Giant Magnetoresistive effect. The magnetic layers of the device align "up" or "down" depending on an external magnetic field. In the simplest case, a spin valve consists of a non-magnetic material sandwiched between two ferromagnets, one of which is fixed (pinned) by an antiferromagnet which acts to raise its magnetic coercivity and behaves as a "hard" layer, while the other is free (unpinned) and behaves as a "soft" layer. Due to the difference in coercivity, the soft layer changes polarity at lower applied magnetic field strength than the hard one. Upon application of a magnetic field of appropriate strength, the soft layer switches polarity, producing two distinct states: a parallel, low-resistance state, and an antiparallel, high-resistance state.