Engineering - Anisotropic Magnetoresistance

Anisotropic Magnetoresistance Anisotropic Magnetoresistance (AMR) is a phenomenon observed in certain materials where their electrical resistance varies with the angle between the electric current and the direction of an applied magnetic field. In other words, the electrical resistance of the material changes depending on the relative orientation of the magnetic field and the current flow. AMR is typically observed in ferromagnetic materials, such as permalloy (a nickeliron alloy) or some rare-earth compounds. These materials have a preferred magnetic orientation, known as magnetocrystalline anisotropy, which influences their electrical properties. When a magnetic field is applied to an AMR material, the resistance of the material changes due to the scattering of electrons as they move through the material. The resistance is lowest when the direction of the current flow is parallel or antiparallel to the magnetic field direction, and it is highest when the current flow is perpendicular to the magnetic field direction. The relationship between the electrical resistance and the magnetic field orientation follows a cosine-squared or cos²θ dependence, where θ is the angle between the current direction and the magnetic field direction. The underlying mechanism behind AMR is the spin-orbit interaction, which couples the magnetic moments of the electrons to their motion and affects their scattering behavior. As the electrons move through the material, their spin orientation interacts with the local magnetic moments, resulting in a change in resistance. AMR has practical applications in various fields, including magnetic field sensing and data storage. In magnetic field sensing applications, AMR sensors are used to measure and detect magnetic fields based on the changes in electrical resistance. These sensors are commonly used in applications such as compasses, magnetic field measurement devices, and non-contact position sensors. In data storage, AMR is utilized in read heads of hard disk drives (HDDs). The resistance change caused by AMR is used to detect the magnetic fields recorded on the spinning disk, allowing the read head to read the data stored magnetically. Overall, the anisotropic magnetoresistance phenomenon is a valuable property o certain materials that enables the development of magnetic field sensors and data storage devices with improved sensitivity and performance.