Strategies to perform magnetization reversals in ferromagnets

A method for performing magnetization reversals in ferromagnets, the method comprising:

• providing a cylindrical ferromagnetic sample having a height dimension along a z-axis that is larger than a diameter dimension in an x-y plane that is perpendicular to the z-axis, the x-y plane defined by an x-axis that is perpendicular to the z-axis and a y-axis that is perpendicular to both the z-axis and the x-axis;
• applying a temporally-varying external field comprising a constant-frequency r.f. Pi pulse to the ferromagnetic sample along a direction perpendicular to the z-axis in the x-y plane, an x-axis component and a y-axis component of the temporally-varying external field each having a magnitude that temporally varies according to a different function of time to cause the temporally-varying external field to continuously rotate a precession magnetization vector around the z-axis, the precession magnetization vector being inclined at an angle with respect to the z-axis;
• applying a temporally-varying external field comprising a temporally-varying magnitude of a z-axis component to the ferromagnetic sample along a direction of the z-axis;
• and
• sweeping a magnitude of the constant-frequency r.f. Pi pulse based on an instantaneous precession frequency and a corresponding angle of inclination of the precession magnetization vector.

A system for reversing a magnetization in a ferromagnet, the system comprising:

• a cylindrical ferromagnetic sample having a height dimension along a z-axis that is larger than a diameter dimension in an x-y plane that is perpendicular to the z-axis, where the x-y plane is defined by an x-axis that is perpendicular to the z-axis and a y-axis that is perpendicular to both the z-axis and the x-axis;
• a first magnetic field generator is configured to apply a temporally-varying external field comprising an r.f. Pi pulse to the ferromagnetic sample along a direction perpendicular to the z-axis in the x-y plane, an x-axis component and a y-axis component of the temporally-varying external field each having a magnitude that temporally varies according to a different function of time to cause the temporally-varying external field to continuously rotate a precession magnetization vector around the z-axis, the precession magnetization vector being inclined at an angle with respect to the z-axis;
• and
• a computer configured to control the magnetic field generator to continuously vary one or more parameters of the temporally-varying external field comprising an r.f. Pi pulse to the ferromagnetic sample along a direction perpendicular to the z-axis in the x-y plane, based on an angular dependence of a precession frequency of the ferromagnetic sample.