New magnetic phase and magnetic coherence in Nd/Sm(001) superlattices

Abstract

In order to investigate magnetic phenomena in Nd and Sm layers separately, resonant x-raymagnetic scattering experiments have been performed to study Nd/Sm(001) superlatticeswith different relative layers thickness. The samples were grown using molecular beamepitaxy, and optimized to yield dhcp Sm growth and thus a coherent dhcp stacking acrossthe Nd/Sm superlattices. The magnetic phases in Sm layers are very close to the onesevidenced in dhcp thick films. In contrast, the magnetism in Nd layers showsstrong differences with the bulk case. In superlattices with a large Sm thickness(>8 nm), no magnetic scattering usually associated with Nd magneticstructure was detected. In superlattices with smaller Sm thickness(<4 nm), new Nd magnetic phases have been observed. A detailed analysis of the propagationof the magnetic structures in the cubic and hexagonal sublattices of both Sm and Nd ispresented. Both Sm hexagonal and cubic magnetic phases propagate coherently through3.7 nm thick Nd layers but remain confined in Sm layers when the Nd layers are 7.1 nmthick. In contrast, the critical Sm thickness allowing a coherent propagation of Nd magneticorder is different for the hexagonal and cubic sublattices above 5 K. Finally, weshow that: (i) a spin-density wave and a 4f magnetic order with perpendicularpolarization are exclusive on a given crystallographic site (either hexagonal orcubic); (ii) a 4f magnetic order on a crystallographic site does not perturb theestablishment of a spin-density wave with a perpendicular polarization on the other site.