| Autor: |
Heiko Bremers, Klaus Wojczykowski, Inga Ennen, Andreas Hütten, Peter Jutzi, O Michele, Günter Reiss, D. Sudfeld, Jiirgen Hesse |
| Rok vydání: |
2004 |
| Předmět: |
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| Zdroj: |
physica status solidi (c). 1:3596-3602 |
| ISSN: |
1610-1634 |
| DOI: |
10.1002/pssc.200405514 |
| Popis: |
The best way to achieve a virgin state of a magnetized sample is to heat it up to a temperature high enough to destroy every magnetic order and thereafter cooling it down in a zero magnetic field. This procedure is often not possible because high temperatures may cause irreversible changes in the sample's constitution e. g. by crystallization in amorphous systems. Because of magnetic history and memory effects it is difficult to measure the same initial magnetization curves after different demagnetizing procedures for materials consisting of nanoparticles with high Curie temperatur TC. Very often the demagnetization by alternating decreasing magnetic fields (AC demagnetization) is used instead. Ferrofluids offer the possibility to demagnetize the sample by heating it above the melting point of the liquid in zero external field. The brownian motion destroys any “frozen in” magnetic order and relieves single domain particles in the fluid. After zero field cooling the virgin state may be reproducibly achieved. We present an experimental study showing the influence of different demagnetization sequences on the initial magnetization curves in frozen ferrofluids. In this contribution we show the deviation between thermally demagnetized and AC demagnetized samples by substracting both initial curves from each other. We detect a “frozen in“ pattern which shows the “steps” of the AC demagnetization sequences. In a further step we focus on the experimental determination of the switching field distribution (SFD) of the particles. We compare the SFD with a plot proposed by Thamm and Hesse (1996). |
| Databáze: |
OpenAIRE |
| Externí odkaz: |
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