  In many applications, the ability to measure the vector information of a
magnetic field with high spatial resolution and low cost is essential, but it
is still a challenge for existing magnetometers composed of multiple sensors.
Here, we report a single-device based vector magnetometer, which is enabled by
spin-orbit torque, capable of measuring a vector magnetic field using the
harmonic Hall resistances of a superparamagnetic ferromagnet (FM)/heavy metal
(HM) bilayer. Under an ac driving current, the first and second harmonic Hall
resistances of the FM/HM bilayer show a linear relationship with the vertical
and longitudinal component (along the current direction) of the magnetic field,
respectively. By employing a L-shaped Hall device with two orthogonal arms, we
can measure all the three field components simultaneously, so as to detect both
the amplitude and direction of magnetic field in a three-dimensional space. As
proof of concepts, we demonstrate both angular position sensing on the three
coordinate planes and vector mapping of magnetic field generated by a permanent
magnet, both of which are in good agreement with the simulation results.
Crosstalk between vertical and longitudinal field components at large field is
discussed using theoretical models.
