Suchergebnisse

Through a combination of atomistic spin-lattice dynamics simulations and relativistic ab initio calculations of electronic transport we shed light on unexplained electrical measurements in nickel nanocontacts created by break junction experiments under cryogenic conditions (4.2 K). We implement post-self-consistent-field corrections in the conductance calculations to account for spin-orbit coupling and the noncollinearity of the spins, resulting from the spin-lattice dynamics. We find that transverse magnetic domain walls are formed preferentially in (111)-oriented face-centered-cubic nickel atomic-sized contacts, which also form elongated constrictions, giving rise to enhanced individual domain wall magnetoresistance. Our calculations show that the ambiguity surrounding the conductance of a priori uniformly magnetized nickel nanocontacts can be traced back to the crystallographic orientation of the nanocontacts, rather than spontaneously formed magnetic domain walls "pinned" at their narrowest points. ; This work was supported by the Generalitat Valenciana through Grant No. PROMETEO2017/139. C.S. gratefully acknowledges financial support from the Dean Fellowship of the Weizmann Institute of Science and Generalitat Valenciana (Grant No. CDEIGENT2018/028). O.T. appreciates the support of the Harold Perlman family, and acknowledges funding by a research grant from Dana and Yossie Hollander, the Israel Science Foundation (Grant No. 1089/15), the Minerva Foundation (Grant No. 120865), and The Ministry of Science and Technology of Israel (Grant No. 3-16244). J.J.P. acknowledges financial support from Spanish MINECO through Grants No. FIS2016-80434-P and No. PID2019-109539GB-C43, the Fundación Ramón Areces, the María de Maeztu Program for Units of Excellence in R&D (Grant No. CEX2018-000805-M), the Comunidad Autónoma de Madrid through the Nanomag COST-CM Program (Grant No. S2018/NMT-4321), the European Union Seventh Framework Programme under Grant Agreement No. 604391 Graphene Flagship, the Centro de Computación Científica of the Universidad Autónoma de Madrid and the computer resources at MareNostrum and the technical support provided by the Barcelona Supercomputing Center (Grant No. FI-2019-2-0007). The SLD and DFT calculations in this paper were performed on the high-performance computing facilities of the University of Alicante and the University of South Africa.

Atomic-sized contacts of iron, created in scanning tunneling microscope break junctions, present unusually high values of conductance compared to other metals. This result is counterintuitive since, at the nanoscale, body-centered-cubic metals are expected to exhibit lower coordination than face-centered-cubic metals. In this work we first perform classical molecular dynamics simulations of the contact rupture, using two different interatomic potentials. The first potential is isotropic, and produces mostly single-atom prerupture contacts. The second potential accounts for the directional bonding in the materials, and produces mostly highly coordinated prerupture structures, generally consisting of more than one atom in contact. To compare the two different types of structures with experiments, we use them as input to density functional theory electronic transport calculations of the conductance. We find that the highly coordinated structures, obtained from the anisotropic potential, yield higher conductances which are statistically in better agreement with those measured for body-centered-cubic iron. We thus conclude that the directional bonding plays an important role in body-centered-cubic metals. ; This work was supported by the Generalitat Valenciana through PROMETEO2017/139 and GENT (CDEIGENT2018/028), the Spanish government through Grants No. MAT2016-78625-C2-1-P and No. FIS2016-80434-P, and the Spanish Ministry of Science and Innovation, through the "María de Maeztu" Programme for Units of Excellence in R&D (CEX2018-000805-M), by Comunidad Autónoma de Madrid through Grant No. S2018/NMT-4321 (NanomagCOST-CM), by the Fundación Ramón Areces, and by the European Union Graphene Flagship under Grant No. 604391.