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M. Cao et al. / Physica B 364 (2005) 150–156
magnetization measured from these ‘undoped’
CaB as a function of Fe content measured by
ICP method. They lie below the line expected if all
the Fe impurities are stabilized as FeB, i.e. the
amount of ‘native’ Fe content in the ‘undoped’
material chemistry of CaB6 with Fe impurity
allows significant magnetization behaviors to be
observed. This shows the importance of taking
into account the trace magnetic elements in
studying the weak ferromagnetism in metallo-
boron compounds.
6
CaB materials is more than enough to account
6
for the observed ferromagnetism. In Fig. 6, the
hysteresis loop of the undoped CaB sample is also
6
shown, its shape is almost similar with those of the
doped Fe samples, so we may conclude that weak
ferromagnetism observed in CaB6 is mostly of
extrinsic origin caused by FeB particles. This
phase identification is consistent with the Curie
temperature measurement of 600 K for weak
ferromagnetism reported in CaB6 and in FeB
whose Curie temperature is 598 K. Lofland et al.
Acknowledgements
This work is supported by the Hundred-Talent
Fund of Tsinghua University and the Postdoctoral
Research Foundation of the Chinese Education
Ministry.
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