Memory effect and generation-recombination noise of magnetic monopoles in spin ice

We theoretically investigate the generation-recombination processes of magnetic monopoles in spin ices. We calculate the spectrum of the relative fluctuations of the numbers of pairs of magnetic monopoles, directly related to that measurable of the magnetic flux noise, using the Langevin approach, previously proposed. Measurements of spectral density of magnetic-flux noise, recently, gave an experimental confirmation of our theoretical results. The agreement with the experimental results is obtained by suggesting a model for the total spectrum of relative fluctuations, which consists in superimposing the spectra of a set of generation-recombination processes, characterized by different time constants and a given probability density function. (nesmcq18)