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XRD scan revealing the formation of nanomagnets. Beside the main peaks from Ge(004) and Ge(002), the diffraction peaks of (111), (002), (310), (222), and (004) are clearly visible.
Temperature dependent memory effect in the dc magnetization. The dashed line (red) is measured during cooling in 50 Oe at a cooling rate of 1 K/min, while the solid line (black) is measured in 50 Oe with the same cooling rate but with a stop of 2 h at 200, 150, 100, 50, and 20 K. The field is cut off during stop. The magnetization change before and after stopping is observed at 150 K. The dotted line (blue) is measured with continuous heating at the same rate after the previous cooling protocol. Inset (a): Hysteresis loop measured at 5 K. Inset (b): time dependent remanent magnetization measured after cooling from 300 to 100 K with a field of 50 Oe. Scattered symbols are experimental data and the solid line (blue) is a fitting using the stretched-exponential function [Eq. (1) ].
Magnetic relaxation after field cooling (a) with temporary cooling at and (b) with temporary heating at . The insets plot the same data vs the total time spent at 100 K. The relaxation curve during is the continuation of that during after temporary cooling, but not after temporary heating. After temporary heating, no memory effect is observable.
Comparison between different magnetization quantities depending on temperature (a) ZFC/FC curves using a field of 50 Oe. The magnetic remanence is also shown. To measure the magnetic remanence, a field of 8000 Oe was applied to saturate the magnetization at 5 K and the remanence was measured during warming in a zero field. (b) The differential of magnetic remanence vs temperature revealing a broad minimum indicated by the arrow. (c) The magnetization change before and after stopping ( as shown in Fig. 2 ) and the relaxation time obtained by fitting using Eq. (1) .
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