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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
Dienstag, 28. März 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.