Figure 3: Ac-magnetricity and monopole diffusion in spin ice, Dy2Ti2O7.
From: Brownian motion and quantum dynamics of magnetic monopoles in spin ice
A representative fit to the ac-magnetization data at 
: (a) real and (b) imaginary susceptibilities and (c) Cole–Cole plot (an argand diagram). The lines (red, T=4.5 
; blue, T=8 
; green, T=14 
) fit all data with the same set of four parameters at a given temperature: 
, 
, 
and 
, as defined in the text. (d) Monopole mobility measured at applied fields 
(full black circles), 3 (full dark grey), 10 (full light grey), 18.5 (open black) and 38.5 (open grey) 
. Error bars represent the s.d. The red line is 
where 
 
. This is characteristic of Brownian diffusion of monopoles with a temperature-independent diffusion constant (inset). The blue line is 
where 
 
, 
 
, characteristic of a previously identified Orbach-like spin flip process arising from the coupling to excited crystal field states. This process is extinct below 
 
, giving way to monopole diffusion as the cause of magnetic relaxation in spin ice.
