Estimating Thermally Driven Magnetic Field Fluctuations near Nanoscale Ferromagnets - Understanding Signal Loss in Magnetic Resonance Force Microscopy (MRFM)*

Many spin-based quantum computing proposals involve carrying out electron or proton (spin) magnetic resonance very close to a magnet [1]. Additionally, nitrogen-vacancy center imaging and magnetic resonance force microscopy (MRFM) employ nanoscale magnets close to spins [2,3]. One potential problem in these experiments is loss of signal due to unwanted spin-lattice relaxation caused by stochastic magnetic field fluctuations [4]. We present a novel simulation protocol - ground, excite, ring, Fourier transform (GERFT) - to estimate thermomagnetic fluctuations in nanoscale ferromagnets. Using NIST's Object Oriented Micromagnetic Framework (OOMMF) code, we apply a pulsed magnetic field at a point of interest, calculate the resulting transient change in magnetization at each location in the ferromagnet, and use a Fourier transform fluctuation-dissipation theorem relation to compute the power spectral density of field fluctuations at the point of interest. GERFT estimates spin-lattice relaxation times due to fluctuations from common ferromagnetic materials to be 6-7 orders of magnitude longer than would cause significant signal loss in MRFM experiments. The insights provided by this model will lead to higher resolution spin imaging experiments and better designed quantum spintronic devices.

1. Loss, et al. Physical Review X (2013) 3: 041023

2. Yacoby, et al. Nature Nanotechnology (2014) 9: 279-284.

3. Rugar, et al. PNAS (2009) 106(5): 1313-1317.

4. Rugar, et al. Phys. Rev. Lett. (2001) 87: 277602.