70
R. Mathieu and P. Nordblad
20
30
40
50
60
70
T(K)
0
5
10
15
20
25
30
M/H (arb. units)
0
log 10 t (s)
0
2
4
M/H (arb. units)
20
40
60
T (K)
-2
-1.5
-1
-0.5
0
0.5
M/H (arb. units)
60
80
100
120
140
160
180
T (K)
0
1
2
3
4
5
6
7
M/H (SI)
0
2
4
log 10 t (s)
0
0.1
0.2
M/M
max FC
60
100
140
T (K)
-0.4
-0.3
-0.2
-0.1
0
0.1
M/H
RCP8, T h /T g = 0.8
Cu(Mn), T h /T g = 0.7
t w = 0
t w = 0
3000 s
10 000 s
Fig. 3.4 M/H versus T (main frames) and M versus log (t) (upper insets) for an archetypal spin glass
(top, Cu(Mn)) and a compacted ensemble of 8 nm maghemite nanoparticles (bottom, RCP8); H =
0.5 Oe. In the latter case, corrections due to demagnetization effects have been made to extract the
internal susceptibility. The main frames illustrate memory behaviour (lower insets show difference
curves = M mem -M ref ) and the upper insets magnetization relaxation curves measured after
two different wait times t w as indicated in the figure