Emerging magnetic order in platinum atomic contacts and chains

Abstract

The development of atomic-scale structures revealing novel transport phenomena is a major goal of nanotechnology. Examples include chains of atoms that form while stretching a transition metal contact or the predicted formation of magnetic order in these chains, the existence of which is still debated. Here we report an experimental study of the magneto-conductance (MC) and anisotropic MC with atomic-size contacts and mono-atomic chains of the nonmagnetic metal platinum. We find a pronounced and diverse MC behaviour, the amplitude and functional dependence change when stretching the contact by subatomic distances. These findings can be interpreted as a signature of local magnetic order in the chain, which may be of particular importance for the application of atomic-sized contacts in spintronic devices of the smallest possible size.

Magnetism in Pd: Magnetoconductance and transport spectroscopy of atomic contacts

“…All observations made here so far are comparable with earlier results on atomic Pt contacts [21] but in stark contrast to the features reported for nanoscale Pd contacts [ 19] where the effects are monotonous, much larger, and occur at larger contact sizes and lower magnetic fields. These discrepancies may be due to the different sample design, since the samples investigated in Ref.…”

“…[ 19] large magnetoconductance effects at field scales of only a few tens of millitesla have been reported in Pd nanojunctions and were interpreted as a sign of magnetic order. Similarly, our study on the magnetoconductance of Pt atomic contacts evidenced the existence of magnetic order at the atomic scale [21]. In contrast to the findings in nanometer-sized Pd, the effects in Pt vanished for contacts larger than a few nanometers.…”

“…The microscopic origin ofthese differences may be understood considering the atomic and electronic configuration of the junctions and their effect on the MC behavior. In a minimal model, similar to the one reported for Pt [21], the junction consists of three distinct parts, i.e., the central atom, the apex atoms, and the tips of the electrodes (see also The magnetic state in an atomic-size contact is defined by contributions of different parts: the electrodes (blue), the apex atoms (magenta), and the central atom (cyan). Each of these parts is characterized by a different magnetic moment and magnetic anisotropy energy, which depend on the electronic and geometric environment.…”

“…This value is chosen below the bulk phonon modes of Pd (16 me V) [71] in order to account for phonon softening in the atom-sized contact [72,73]. The results of the analysis are compared to those of Au contacts, where conductance fluctuations were intensively studied before [5,21]. Calculations reported in literature [62,[64][65][66] (5) where e is the electron charge, h Planck's constant, a the diameter of the sample, and le the electron mean free path.…”

“…The voltages as well as the differential voltages over the sample and reference resistor are measured simultaneously with multimeters and by means of the lock-in technique. After cooldown in a cryogenic vacuum to 4.2 K we perform a soft electromigration process to reduce crystal defects and remove contaminations from the fabrication process in the constriction [21]. Subsequently, a conductance histogram is recorded by repeatedly opening and closing the junction at low applied de voltage of~ I m Vat the sample to determine the preferred conductance values of the Pd atomic contact and verify the purity of the sample.…”