Proximity effects and exchange bias in Co/MnF₂(111) heterostructures studied by x-ray magnetic circular dichroism

Abstract

Cobalt nano-structured ultrathin films were grown on orthorhombic MnF(2) by molecular beam epitaxy on CaF(2) epitaxial layers deposited on Si(111) substrates. The Co film was grown at room temperature. It was found to be polycrystalline, forming nano-islands with height≈diameter≤10 nm. X-ray absorption evidences the chemical stability of the Co/MnF(2) interface. Remarkably, x-ray magnetic circular dichroism (XMCD) demonstrates that the Co induces a net magnetization on the Mn ions close to the interface. The magnetic moments of these Mn ions couple antiparallel to the Co and rotate upon field reversal following the magnetization of the Co both below and high above the Néel temperature of MnF(2) (T(N) = 67 K). The density of coupled Mn moments is found to be temperature dependent, with an equivalent thickness of ~1.5 MnF(2) monolayers at 20 K, decreasing to about ~0.5 ML as the temperature is raised to 300 K. Interestingly, the intensity of the Mn XMCD signal appears to be related to the coercivity of the Co layer. This behavior is interpreted in terms of the competition between thermal fluctuations, exchange coupling between Co and Mn at the interface and, at low temperature, the antiferromagnetic order in MnF(2).

A look inside epitaxial cobalt-on-fluorite nanoparticles with three-dimensional reciprocal space mapping using GIXD, RHEED and GISAXS

“…One of the possible technologies to produce such systems is epitaxial deposition of ferromagnetic metals (Co, Ni, Fe) on nonmagnetic (CaF 2 ) and antiferromagnetic (MnF 2 , NiF 2 ) insulating fluoride layers grown on Si. Such heterostructures provide a suitable framework to study properties of the twodimensional magnetically ordered nanoscale systems (Suturin et al, 2013).…”

An advanced three-dimensional RHEED mapping approach to the diffraction study of Co/MnF2/CaF2/Si(001) epitaxial heterostructures

“…Cobalt nanoparticles were deposited on top of the MnF 2 layer using an e-beam evaporation source at a rate of $0.2 nm min À1 . A total of 3-5 nm of cobalt was deposited on MnF 2 at room temperature to perform a comparison with the similar samples of MnF 2 /CaF 2 /Si(111) studied previously (Suturin, Fedorov, Banshchikov et al, 2013). Small cobalt nanoparticles may be recognized in Figs.…”

“…Growth of ferromagnetic Co layers and Co island arrays on fluoride surfaces has been recently studied by Suturin, Fedorov, Banshchikov et al (2013) and Suturin, Fedorov, Korovin et al (2013). Magnetic proximity effects in Co/MnF 2 / CaF 2 (111)/Si(111) heterostructures have been reported by Suturin, Fedorov, Banshchikov et al (2013).…”

Hysteresis enhancement on a hybrid Dy(iii) single molecule magnet/iron oxide nanoparticle system

“…36,49,81 Exchange bias has been observed in core-shell NP, 49 in coupled aggregates of SMMs 82,83 or on SMMs coupled to a magnetic surface 33,84 additionally to the seminal studies on biasing on heteromagnetic multilayers. 81,85,86 To ascertain the origin of the enhanced hysteresis in NP-Dy12 X-ray magnetic circular dichroism (XMCD) data were collected at the Fe L2,3 and Dy M4,5 edges, which reveal the element specific contributions to the magnetic properties. The strength of the XMCD signal is known to be proportional to the total, spin and orbital, magnetic moment localized in the Fe 3d and the Dy 4f shells, respectively.…”