The giant planar Hall effect

Is a new type of magnetoresistance (MR) seen in a ferromagnetic semiconductor by a team of physicists from Caltech and the University of California, Santa Barbara. In the usual Hall effect, current flowing along a planar conductor is slightly swept to the side when a magnetic field, oriented perpendicular to both the current and the plane, is turned on. In the new experiment, the applied magnetic field lies in the conducting plane, at some angle to the current. The physicists found that, for all nonzero angles—except those aligned with directions of high crystallographic symmetry—there were always two large and abrupt jumps in the Hall voltage as the magnetic field strength was varied. This type of anisotropic MR switching behavior was previously seen in magnetic metals, but the effect in the magnetic semiconductor (GaMnAs) is a factor of 10⁴ stronger. MR effects are important in the huge magnetic read-head industry and are also central to the development of spintronics, in which an electron’s spin, not just its charge, is instrumental in carrying out high-speed operations. ( H. X. Tang et al. , Phys. Rev. Lett. 90, 107210, 2003.)