Magnetic structures of Laves phase superlattices

Abstract

We present a determination of the magnetic structuresof three Laves phase superlattice samples of structure[70/30]60,[150/100]50,and [50/70]60,where the structure is given as [t1 Å DyFe2/t2 Å YFe2]N,grown by molecular beam epitaxy. The experiments were performed usingmagnetization measurements and neutron scattering measurements at the NRUreactor at Chalk River in Canada.For the [70/30]60sample, a magnetic field parallel to the scattering vector, Q,was applied to determine the nuclear component of the scattered intensity. Themagnetic structure with the field aligned along the [001] had all the momentsaligned along the field direction and the magnitude of the moment on the iron sitewas temperature independent with a value of 2.3(0.3) μB.The moment on the dysprosium site was found to decreasewith temperature from about 10 μBto a value of 6(0.5) μBat 300 K. When the field was applied in the [11̄0]direction the magnetic moments were found to rotate out of the(110)epitaxial plane towards the [110] direction by an angle ψ = 10°at 300 K, which increased at 4 K to an angle of ψ = 40° close tothe [100]out-of-plane direction.For the [150/100]50sample, when a 6 T magnetic field was applied along the [11̄0]direction, the main peak of the magnetically sensitive (111̄)reflection was found to decrease in intensity while the scatteringat the satellite peaks increased. This change in intensity is due tothe formation of magnetic exchange springs in the ‘soft’ YFe2layers of the superlattice. Detailed measurements around the (111̄)reflection and calculations for an exchange spring model give excellent agreementbetween the model and the experiment.Finally, the [50/70]60sample showed unexpected behaviour because the moments aligned largelyperpendicular to an applied field. This is similar to a spin-flop phase of anantiferromagnet and it is argued that this occurs because the net moments on the DyFe2 andYFe2layers are nearly equal.