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Regensburg 2000 – scientific programme

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AM: Magnetismus

AM 13: Postersitzung: Dünne Schichten (1–22), Magnetowiderstand (23–40), Phasenübergänge (41–55), Mikromagnetismus (56–68), Spektroskopie (69–77), Nanokristalline Materialien (78–82), Anisotropie (83–86), Schmelzen (87–90), Weitere Bereiche (91–100)

AM 13.96: Poster

Tuesday, March 28, 2000, 16:00–20:00, A

New methods of magnetic heat capacity measurements based on SQUID magnetometry — •A. Kharkovski, Ch. Binek und W. Kleemann — Angewandte Physik, Gerhard-Mercator-Universität Duisburg, 47048 Duisburg

We measure the temporal relaxation of the field induced magnetic moment m of an antiferromagnetic FeBr2 sample. It relaxes into a new equilibrium state on applying a steplike increase of the optical heating power W of a Laser light source. The power is optimized in order to obtain a small stationary temperature growth of ΔT<0.1 K. A SQUID magnetometer detects the resulting exponential relaxation of m. It is characterized by a single time constant τ=C R. Its value is determined by the absolute heat capacity C of the sample and the heat resistance R=ΔT/W between the sample and the surrounding He-heat bath. Using the sample itself as a temperature sensor, the light-induced temperature change δT is determined from m(T) and m(T+ΔT) with and without light exposure, respectively. The heat capacity is then calculated according to C=τW/ΔT. This relaxation method is compared with the thermal SQUID susceptometry, which is based on a periodic modulation of the light power. In accordance with the temporal exponential relaxation, the frequency dependence of m=m’- im” is well described in the framework of a Debye-model. Both methods are used to clarify subtle details of the magnetic heat capacity of FeBr2 in axial magnetic fields.
Work supported by DFG.

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