The Giant Planar Hall Effect

The Giant Planar Hall effect is the name for a new type of magnetoresistance (MR) seen in an experiment with ferromagnetic semiconductors performed by a Caltech-UC Santa Barbara team of physicists. MR effects are important in the huge magnetic read-head industry (where a tiny magnetic artifact, such as a magnetic bit written in a storage medium, is transformed into a large electrical artifact signal, such as an abrupt change in resistance) and are also central to the development of spintronics, the new form of electronics in which electron spin and not just electron charge is instrumental in conducting high-speed transactions. In the usual Hall effect, current flowing along a planar conductor is slightly swept to the side when a magnetic field, oriented perpendicular to the current and to the plane, is turned on. In the Caltech-UCSB experiment, the applied magnetic field lies in the conducting plane, and the result is to lower resistivity along several specific directions, encouraging a corresponding pattern of current flow. This type of anisotropic MR has previously been seen in magnetic metals, but the effect was weak. In the present experiment, carried out with a magnetic semiconductor (GaMnAs), the effect is 10⁴ times stronger. For this reason Michael Roukes (626-395-2916) believes that once the temperature at which the materials can no longer retain a magnetic orientation (the "Curie temperature") can be raised to more practical levels (this experiment was carried out at below 45 K), the giant planar Hall effect could hasten the onset of better magnetic resonance microscopy and magnetic random access memory (MRAM) components, advanced magnetic sensors and memory components, and, perhaps ultimately elements for solid-state quantum computers. (Tang et al., Physical Review Letters, 14 March 2003, contact also David Awschalom).