Exchange bias in reduced dimensions: Cobalt nanocluster arrays under the influence of nanometer thin MnPt capping layers

Abstract

The magnetic behavior of cobalt nanocluster arrays arranged on a boron-nitride nanomesh and capped with MnPt layers of varying thickness θMnPt is investigated. The magnetic properties of the arrays are found to be strongly dependent on the cobalt nanocluster size: large 3-dimensional clusters of several nanometers size under the influence of only θMnPt∼5 nm exhibit prototypical exchange bias behavior, whereas small 2-dimensional clusters of about 1 nm in diameter show superparamagnetic behavior, however, with a strong quenching of the average cobalt magnetization. The latter effect is correlated with the formation of a stable antiferromagnetic phase at increasing θMnPt and is discussed in terms of the domain state exchange bias model. The quenching suggests either partial antiferromagnetic alignment of cobalt spins within a cluster or a random orientation of cobalt cluster macrospins with respect to each other.

Magnetism and morphology of Co nanocluster superlattices onGdAu2/Au(111)–(13×13)

“…This strain relief pattern is an ideal template for the self-assembly of magnetic nanocluster superlattices [1] as it features a hexagonal array of preferential nucleation sites with the extremely high density of 53 Tera/inch 2 [2,3]. Previous reports of room-temperature magnetic remanence for Co nanoclusters on this surface [4] spurred further investigation on this system, motivated also by the behavior reported for Co nanocluster arrays grown on other templates, such as Au(788) [5], graphene/Ir(111) [6], and hexagonal-BN/Rh(111) [7], which are superparamagnetic down to 40 K or even below. For a nanocluster, the observation of magnetic remanence at a given temperature critically depends on its magnetic anisotropy energy (MAE), which is influenced by the cluster size and shape, as well as by its interaction with the substrate.…”

High Temperature Magnetic Stabilization of Cobalt Nanoparticles by an Antiferromagnetic Proximity Effect

“…Despite the foreseeable change of recording paradigm from continuous to patterned media, where each bit is recorded in an individual nanostructure [7], the key for sustained storage density increase will remain the introduction of progressively more anisotropic (high K) materials [8], which allow for magnetic stability at very small volumes, V (i.e., blocking temperature, T B ∝ KV, above room temperature, RT). Two main strategies are largely investigated to achieve high K (both of them with implications in other active technologies beyond information storage, such as permanent magnets, magnetic hyperthermia or even sensors [5,[9][10][11]): (i) the use of compounds with intrinsically high magnetocrystalline anisotropy (such as FePt [3,8]) and (ii) the design of exchange-coupled nanocomposites [4,[12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29].…”

Fe-Phthalocyanine Nanoclusters on La0.67Sr0.33MnO3 Ferromagnetic Substrate for Spintronics Application

“…4,5 In the hybrid organic/inorganic interface for spintronics applications both the nano-objects and their magnetic response are the main ingredients with which to play. 6 In particular, the magnetocrystalline anisotropy and the superparamagnetic blocking temperature may vary depending on the nanoobjects' morphologies, compositions, and the magnetic interaction among them and with the supporting medium. For example, it was observed that the low temperature magnetic response depends on the magnetic interface anisotropy in the case of cobalt nanoclusters in contact with metal surface through a buffer Xe layer.…”

“…In the hybrid organic/inorganic interface for spintronics applications both the nano-objects and their magnetic response are the main ingredients with which to play . In particular, the magnetocrystalline anisotropy and the superparamagnetic blocking temperature may vary depending on the nano-objects’ morphologies, compositions, and the magnetic interaction among them and with the supporting medium.…”