Magnetism and local order in dilute FeCo alloys

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Abstract
The coupling between magnetism and chemical short-range order (SRO) is investigated in ferromagnetic alloys through an experimental investigation of the temperature dependence of the local order in both ferromagnetic and paramagnetic phases around the Curie temperature. Experiments were carried out in quenched dilute FeCo alloys through zero-field NMR at 59Co nuclei. The conditions which allow the equilibrium SRO parameters to be obtained and their temperature variation to be measured from low-temperature NMR spectra are carefully discussed. An abrupt change in the behaviour of the local order is observed at the Curie temperature. The authors use a very simple theoretical model based on an Ising-Heisenberg Hamiltonian to account qualitatively for the experimental results. They point out the importance of the magnetic coupling on the chemical SRO so that measurement of local order in equilibrium states allows only a combination of chemical and magnetic pair interactions to be determined.