Transition-metal dimers and physical limits on magnetic anisotropy

Abstract

Interest 2 in magnetic nanoparticles, which typically contain tens of thousands of magnetic atoms, has been spurred both by the crucial role that they play in advanced magnetic information storage devices, and by the light that investigating magnetism at the nanoscale sheds on the fundamental interactions responsible for the magnetic state.As the frontier advances, interest is shifting to still smaller size scales. Dimers represent the small size end point in the transition metal cluster crossover from nanoparticle 2 to molecular magnetic properties. The magnetic moments per atom in clusters of the 3d

Extremely large perpendicular magnetic anisotropy of an Fe(001) surface capped by5dtransition metal monolayers: A density functional study

“…For instance, in a Co atom, a large MCA of 9.3 meV/atom (about 200 times larger than that in bulk Co) was observed in Co adsorbates on a Pt substrate. 23 Theoretical studies predict that extremely low-dimensional 4d and 5d TM systems, such as atomic dimers 24,25 and atomic chains, 18,19 can have fairly large MCAs on the order of tens of meV/atom, which are enhanced even more as the interatomic distances increase. Moreover, the small MCAs of Co and Fe are enhanced when Co monolayers (ML) on Au(111) 26 and Fe MLs on Pt(001) surfaces 27 are capped by additional Au and Pt layers, respectively.…”

Anisotropic magnetoresistance in nanocontacts

“…As a result, the orbital moment of magnetic atoms and their magnetic anisotropy energy ͑MAE͒ depend strongly on their atomic coordination. 1,2 The transport counterpart of MAE is anisotropic magnetoresistance ͑AMR͒, i.e., the dependence of the resistance on the angle between the magnetization and the current flow. Whereas AMR in bulk was known back in the 19th century and is a rather small effect, the recent observation of AMR in a variety of low dimensional systems, [3][4][5][6][7][8][9][10][11][12] largely exceeding bulk values, has opened a new research venue in the field of spin-polarized quantum transport.…”

“…Here, we consider two different transport regimes: coherent and sequential. In the coherent regime, we use the Landauer formalism that, at zero temperature, relates the zero-bias conductance G to the quantum mechanical transmission of the electrons at the Fermi energy, G = e 2 h T͑⑀ F ͒. This approach accounts for AMR both in the tunneling regime ͑TAMR͒ 20 and in the contact or ballistic regime ͑BAMR͒ 14 in the absence of sharp resonances near the Fermi energy.…”

Giant magnetic anisotropy and tunnelling of the magnetization in Li2(Li1−xFex)N

“…Whereas these are small magnetic units, they are still finite in extent and need to carefully balance coupling between magnetic atoms and isolation of one molecule from the next. Dimers of transition metals, as the small-size end point of SMMs, have been theoretically proposed to be promising candidates for novel information storage devices 6 . An alternative approach for the design of magnetic materials based on a few or even single atoms as magnetic units is ad-atoms on metallic surfaces 7,8 .…”