Small angle scattering of neutrons and x-rays were measured in a range of 0.008 ≤ q [= (4π/λ) sinθ] ≤ 0.2 Å-1 for rapidly quenched La-Fe alloys. As-quenched alloys are superparamagnetic at room temperature and ferromagnetic below about 270 K. Both neutron and x-ray scattering show decreases of the intensity proportional to q-3 for the as-quenched specimen. Little effect was observed on decreasing the temperature to 10 K or with the application of an external magnetic field up to 5 kOe. These facts indicate that the scattering is not of magnetic origin. After an annealing at 350°C for 30 min., the alloys change into antiferromagnets. After heat treatment, the scattering intensity decreased considerably and its q-dependence changed to q-4. These results are discussed based on a two-stage solidification process of the alloy, estimated from magnetic measurements, and the "density variation between random boundaries" model caused by nonmagnetic Fe atoms dissolved at the periphery of La grains.
- Small angle scattering