Europhys. Lett.
Volume 63, Number 1, July 2003
Page(s) 56 - 62
Section Condensed matter: structure, mechanical and thermal properties
Published online 01 June 2003
DOI: 10.1209/epl/i2003-00477-3
Europhys. Lett., 63 (1) , pp. 56-62 (2003)

Observation of spin-lattice coupling in the critical region of $\chem{Fe_{65}Ni_{35}}$

S. V. Grigoriev1, S. V. Maleyev1, A. I. Okorokov1 and H. Eckerlebe2

1  Petersburg Nuclear Physics Institute - Gatchina, St. Petersburg 188300, Russia
2  GKSS Forchungszentrum - 21502 Geesthacht, Germany

(Received 4 July 2002; accepted in final form 8 May 2003)

The nuclear-magnetic interference in the critical small-angle scattering of polarized neutrons from invar $\chem{Fe_{65}Ni_{35}}$ near $T_{\ab{C}}=485$ $\un{K}$ was investigated. The interference caused by the spin-lattice coupling revealed the correlation between critical fluctuations of magnetization and fluctuations of the nuclear density. The magnetic scattering allowed one to unambiguously identify a shape of the scattering objects as one of the critical fluctuation. The q-dependence of the interference scattering revealed that the shape of the scattering nuclear objects is essentially the same as the magnetic one. Therefore, the shape and lifetime of the scattering nuclear object are correlated with and terminated by that of the magnetic fluctuation. It was found that the expansion of the lattice is $(\delta a/a)\approx 0.004$. The range of this expansion is of order 50 $\un{\AA}$ and depends on the temperature and magnetic field.

61.12.Ex - Neutron scattering techniques (including small-angle scattering).
75.40.-s - Critical-point effects, specific heats, short-range order.
75.50.Bb - $\chem{Fe}$ and its alloys.

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