Magnetic structure of dysprosium in epitaxial Dy films and in Dy/Er superlattices

Abstract

We present a magnetization and neutron-diffraction study of the basal plane magnetic structure of Dy epitaxial films and Dy/Er superlattices. The thermal evolution of the magnetic phases, the stability of the helical phase under a magnetic field, the thermal variation of the dysprosium in-plane and c parameters, and of the dysprosium turn angle are successively shown. In Dy/Er superlattices, the dysprosium helix propagates coherently through paramagnetic erbium; at low temperature, individual dysprosium layers undergo a ferromagnetic transition and are coupled antiferromagnetically to each other for erbium layers thicknesses larger than 20 Å. In dysprosium films, as expected from the epitaxy effect, the Curie temperature of dysprosium is reduced if dysprosium is grown on yttrium and increased if it is grown on erbium, whereas it is unexpectedly close to the bulk value in Dy/Er superlattices. This amazing value of the Curie temperature in superlattices is correlated to two main experimentally observed effects: ͑i͒ the magnetoelastic driving force is reduced compared to bulk dysprosium because of the clamped ␥ distortion; ͑ii͒ the difference between the exchange energies in the helical and the ferromagnetic phases is increased compared to the bulk value.

Elastic and inelastic neutron scattering for the study of magnetic thin films and heterostructures

“…the modulated order is less favored by exchange than in bulk Dy. Such feature is consistent with conclusions drawn from measurements of turn angle in Dy/Er bilayers [13]. It could be related to changes in the Dy Fermi surface and likely contributes to the increase of T c in SL's.…”

“…At the difference of Dy, bulk Er exhibits an axial anisotropy along the c-axis. It orders at 85 K in a c-axis modulated phase, develops an in-plane component below 52 K and presents a transition to a conical phase with c-axis ferromagnetic component at 20 K. In this specific system with competing anisotropies, the issue of coherent propagation of Dy in-plane modulated order could be addressed both through paramagnetic and magnetic Er [13,25,26]. Figure 2 presents two elastic neutron scattering spectra that have been measured at 110 K and 10 K with the scattering vector along the c-direction for a [Dy(3.5 nm)/Er(2.3 nm)] 50 superlattice.…”

“…Beyond the investigation of Dy/non-magnetic systems, the study of Dy/Er superlattices comprising two magnetic RE was undertaken [13]. At the difference of Dy, bulk Er exhibits an axial anisotropy along the c-axis.…”

“…We will focus on epitaxially grown dysprosium-based nanosystems [13], chosen to explore the effect of epitaxial strains, reduced dimension and magnetic coupling on magnetic properties. We will also essentially focus on the results that we could obtain from neutronbased investigations.…”

Strain-induced modification of magnetic structure and new magnetic phases in rare-earth epitaxial films

“…Therefore, the modulated magnetic order, intimately correlated with the geometry of the Fermi surface, can be modified in epitaxial films [3]. Moreover, the magnetic properties can be modified via the magnetoelastic interaction.…”