Magnetic properties of ultrathin discontinuous Co/Pt multilayers: Comparison with short-range ordered and isotropicCoPt3films

Abstract

Magnetic properties of thin (Co/Pt) multilayers have been investigated in order to study the dependence of magnetization M , uniaxial anisotropy Ku, and Curie temperature TC on the multilayer thickness, composition and structure. A comparison between epitaxial sub-monolayer multilayers and epitaxial fcc CoPt3 alloy films with large perpendicular magnetic anisotropy (PMA) attributed to growth-induced Co clustering reveals significant differences in the temperature dependence of magnetization M (T), despite the presence of thin planar Co platelets in both cases. Even the thinnest discontinuous multilayered structure shows a Langevin-like M (T), while the alloy films with PMA show a broadened and enhanced M (T) indicating a distribution of environments, including monolayer Co platelets separated by only 1-2 layers of Pt. These differences have been reproduced in Monte Carlo simulations, and are shown to be due to different distributions of Co-Co and Co-Pt nearest neighbors. The relatively uniform Co-Co coordination of even a discontinuous rough multilayer produces a Langevin-like M (T), whereas the broader distribution associated with platelets in the PMA films results in a nearly linear T-dependence of M .

Interface-induced phenomena in magnetism

“…are modified whenever its dimensions become comparable to the relevant magnetic correlation length. As a final comment, since isolated atoms are often magnetic where the associated solid is not, reduced coordination at steps, kinks on steps, and isolated adatoms at surfaces or interfaces between thin films are likely to have significantly different moments (including increased orbital moments) and magnetic anisotropy than interior atoms (Freeman and Wu, 1992; Ney et al ., 2001; Charilaou et al ., 2016). …”

“…Notably, this same interfacial symmetry breaking plus spin orbit coupling can also produce perpendicular magnetic anisotropy, as in e.g ., Co/Pt heterostructures and Co-Pt alloys [Charilaou et al ., 2016]. Perpendicular anisotropy, whether interfacially-induced or intrinsic to the structure, in conjunction with long-range dipolar interactions, induces stripe or bubble domains.…”

Magnetic domain propagation in Pt/Co/Pt micro wires with engineered coercivity gradients along and across the wire

“…This is consistent with the thickness profile shown in Fig. 2 and the corresponding PMA variations discussed in Section 3 [38]. In order to explain the peculiarities of the reversal micromagnetic simulations were used.…”

“…The thinning of the MLs in the taper and the subsequent ion bombardment should lead to an intensive alloying in the edge regions. The literature data [38] show that in spite of this the alloyed regions can preserve the magnetic moment as well as perpendicular anisotropy.…”

Unconventional magnetization textures and domain-wall pinning in Sm–Co magnets

“…All material parameters, e.g., exchange stiffness, saturation magnetization, and magnetocrystalline anisotropy, are affected by the reduced dimensions of the platelets and their interfaces 33 . It is known from thin-film studies that the anisotropy is the most sensitive property and changes drastically depending on the thickness and local atomic arrangements 34 . Given the small volume of the Z phase, its internal magnetic field is strongly affected by the strong exchange field of the surrounding Sm–Co.…”