Giant Magnetoresistance (GMR) is a quantum mechanical effect observed in certain materials, where their electrical resistance changes significantly in response to an external magnetic field. This phenomenon occurs in layered structures of magnetic and non-magnetic materials, allowing for the manipulation of electron spin and charge. GMR is widely used in modern technology, particularly in hard disk drives and magnetic sensors. By detecting small changes in resistance, devices can read data more efficiently, leading to advancements in data storage and processing. This effect has played a crucial role in the development of spintronics, a field that explores the use of electron spin in electronic devices.