Magnetization and magnetization reversal in epitaxial Fe/Cr/Co asymmetric spin-valve systems

Abstract

We have investigated asymmetric Fe/Cr/Co/Cr superlattices with two magnetic layers of Fe and Co, which are different with respect to their magnetic properties: magnetization, coercivity, and magnetic anisotropy. The magnetic layers are weakly coupled via a mediating Cr spacer layer providing an antiferromagnetic alignment of adjacent layers. The magnetic structure of these spin-valve-like Fe/Cr/Co/Cr superlattices was analyzed from the remanent state up to saturation via polarized neutron scattering and polarized neutron reflectivity (PNR). Furthermore, the domain structure in remanence was imaged via polarized x-ray photoemission electron microscopy (XPEEM). This analysis reveals that the Co magnetization strongly affects the Fe domain structure, while the layer magnetization is collinear from the remanent antiparallel state up to the ferromagnetic saturation state. However, for certain Co layer thicknesses, the as-grown remanent state exhibits a noncollinear antiferromagnetic spin structure, which cannot be recovered after applying a magnetic field. However, the noncollinear structure is reproducible with freshly grown superlattices.

Structural and Magnetic Properties of Epitaxial FexCo100-xAlloys Grown on Cr Substrate

“…This study was also significantly motivated by the surface induced unusual magnetic properties of spin reorientation transition on Cu (100) [5] and order-disorder magnetization on C (100) [6] with the Fe concentration of epitaxial grown ultra thin Fe x Co 100-x alloy. In particular, it has been reported that molecular beam epitaxially (MBE) grown ultra thin film of Fe and Co forms a superlattice structure on the Cr interface layer [7,8]. This report focuses on illustrating a nonmonotonic increase in the H c and relative magnetic moment with Fe concentration on Fe x Co 100-x /Cr (100).…”

Laterally patterned spin-valve superlattice: Magnetometry and polarized neutron scattering study

“…4 In Ref. 5, it was shown that the non-collinearity of the layer magnetization may even be induced by stray fields from already deposited ferromagnetic domains acting on the magnetic alignment of the spins of atoms arriving at the surface of a growing film. Even more complex are asymmetric superlattices of the type [F 1 /N/F 2 /N] Â n with different ferromagnetic layers F 1 and F 2 .…”

“…This was recently demonstrated for laterally extended [Fe/Cr/Co/Cr] superlattices using Polarized Neutron (specular) Reflectivity (PNR) and Polarized Neutron (off-specular) Scattering (PNS) methods. 5 In this contribution, we aim to study the magnetic properties of asymmetric [Fe/Cr/Co/Cr] superlattices which are laterally patterned into an array of parallel stripes. Patterning first of all introduces a uniaxial shape anisotropy, the strength of which depends on the aspect ratio of the stripes (length versus width).…”

“…For extended [Fe/Cr/Co/Cr] superlattices, in particular, the Co layers remain in a ripple domain state induced by the competition between local anisotropy and exchange interaction, reducing severely the layer magnetization. 5 Patterning may overcome this problem and turn the Co layers into a single domain state. Furthermore, we have to consider that neighboring stripes in an array may experience dipolar coupling via stray fields in the gaps between the stripes.…”

SuperADAM: Upgraded polarized neutron reflectometer at the Institut Laue-Langevin

“…The most complete information is then gained if the neutron polarization of the scattered neutrons is analyzed for various spin states of the incident beam with respect to specular reflectivity and offspecular scattering. Polarized neutron reflectivity (PNR) is mainly used for the investigation of magnetic thin films, 14 superconducting thin films, 15,16 magnetic domains in continuous superlattices, [17][18][19][20][21] or laterally micro-and nano-patterned multilayers. [22][23][24][25][26][27] A detailed account on polarized neutron reflectometry is available in recent reviews.…”