Effect of tilted magnetic fields on bistable nanomagnets in hybrid semiconductor/ferromagnet devices

Using the anisotropic Hall effect in a sub-micron lithographically well-defined two-dimensional electron system we measure the stray field of individual ferromagnetic nanoparticles in tilted magnetic fields. Our model calculations and experimental data show that one can map out the particle's hysteresis loop in great detail even if the field H-app is tilted away from the specimen's easy-axis by an angle phi(app) around 90 degrees. The investigated Ni nanomagnets exhibit a well-defined remanent 'up'- and 'down'-state. For the angular-dependent switching we find two different regimes: below a critical angle phi(c), the hysteresis loop is irreversible and squared, for phi(c) < phi(app) less than or equal to 90 degrees it becomes partly reversible, but discontinuous jumps are still resolved. This characteristic switching behavior is found to depend on the nanomagnet's diameter. (C) 2000 Elsevier Science B.V. All rights reserved.