Is giant magnetoresistance the same as tunnel magnetoresistance?
That's a common misconception, but they are distinct effects. Giant magnetoresistance, or GMR, occurs in metallic multilayers where electrons travel through non-magnetic spacer layers—like chromium or copper—and scatter at interfaces. Tunnel magnetoresistance, or TMR, uses an insulating barrier, such as magnesium oxide, between two magnetic layers. In TMR, electrons quantum-mechanically tunnel through the barrier, and the resistance change can be even larger—over 100% at room temperature. Both rely on spin-dependent transport, but the physics is different. GMR was discovered first, in 1988, and TMR was later optimized, notably by Stuart Parkin and others. In my view, both are essential for spintronics. GMR revolutionized hard drives, while TMR is now used in magnetic random-access memory, or MRAM. The key is to understand that each has its own advantages: GMR for simplicity and TMR for higher signal. Nature is full of surprises—you just have to be ready to explore both paths.
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