Sample spin distribution

In the mrfmsim package, we can simulate the response of a single spin or an ensemble of spins to an external magnetic field. Use the “spin_density” parameter in the Sample object to adjust the target spins for a given grid. See mrfmsim.Sample for more details.

Uniformly distributed sample

For a uniformly distributed spin sample, input the per \(\mu m^3\) value for “spin_density”.

from mrfmsim.component import Sample
sample = Sample(
    spin='e',
    temperature=4.2,
    T1=1e-3,
    T2=250e-9,
    spin_density=2.41e-2)

Non-uniformly distributed sample

For a non-uniformly distributed spin sample, input the spin distribution array for “spin_density”. The array should have the same shape as the grid. For example, for a (10, 10, 10) shaped grid and an array of (4 \(\times\) 4 \(\times\) 4) single spins in the center, the input should be:

from mrfmsim.component import Sample

# for a (10, 10, 10) shaped grid
import numpy as np
spin_density = np.zeros([10, 10, 10])
spin_density[3:7, 3:7, 3:7] = 1
sample = Sample(
    spin='e',
    temperature=4.2,
    T1=1e-3,
    T2=250e-9,
    spin_density=spin_density)

Note

The Grid object does not handle spin locations that are not on the grid points. The mrfmsim system is capable of handling a non-uniform grid system. A custom Grid class can be implemented to handle this. (The feature is currently unimplemented, but it is on the roadmap.) For a small number of spins, we can manually input the spin locations, shape, and origin to the experiment object by removing the “component_replacement” in the Experiment object.

Single spin directly under a spherical magnet

For a single spin directly under a spherical magnet, the signal can be calculate directly.

mrfmsim.experiment.CermitSingleSpinGroup

Simulates an MRFM experiment in the "hangdown" or SPAM geometry where a single electron spin is located directly below the tip.