Europhys. Lett.
Volume 73, Number 3, February 2006
Page(s) 396 - 400
Section Condensed matter: electronic structure, electrical, magnetic, and optical properties
Published online 23 December 2005
Europhys. Lett., 73 (3), pp. 396-400 (2006)
DOI: 10.1209/epl/i2005-10409-3

Experimental critical exponents of "pure" ferromagnets: The cost of excessive proximity to $\mth{T_{\ab{C}}}$ may be too high

M. D. Kuz'min1 and A. M. Tishin2

1  IFW Dresden - PF 270116, D-01171 Dresden, Germany
2  M. V. Lomonosov Moscow State University - 119992 Moscow, Russia

received 10 November 2005; accepted in final form 5 December 2005
published online 23 December 2005

The limited purity of available ferromagnetic materials may turn into a pitfall in experimental studies of critical phenomena. In pursuit of asymptotic critical behaviour it is not uncommon to approach the Curie point too closely, violating the condition $\vert \varepsilon \vert \gg \Delta
T/T_{\ab{C}}$, $\varepsilon = (T-T_{\ab{C}})/T_{\ab{C}}$ (here $\Delta T \sim \Delta x \times 10^{3}\un{K}$ is the width of the critical region, $\Delta x$ being the fractional impurity content). If this happens, the presence of what is normally regarded as a tiny amount of impurity can no longer be neglected. One of the consequences is that the critical exponent $\beta$ is noticeably over-estimated in comparison with its value in the pure material (which is the quantity sought in such studies). This problem does not occur if the excessive proximity to the Curie point is avoided.

75.40.Cx - Static properties (order parameter, static susceptibility, heat capacities, critical exponents, etc.).
75.50.Cc - Other ferromagnetic metals and alloys.

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