Individual Atomic-Scale Magnets Interacting with Spin-Polarized Field-Emitted Electrons

Anika Schlenhoff, Stefan Krause, Andreas Sonntag, and Roland Wiesendanger

Phys. Rev. Lett. 109, 097602 – Published 28 August 2012

Abstract

We resonantly inject spin-polarized field-emitted electrons in thermally switching nanomagnets. A detailed lifetime analysis as a function of the spin-polarized emission current reveals that considerable Joule heating is generated, and spin-transfer torque results in a directed switching. A trend of higher switching efficiency per electron is observed with an increasing emission current, probably due to the excitation of Stoner modes. On a quasistable nanomagnet, a spin-polarized emission current in the low nA regime already triggers magnetization reversal, thereby demonstrating the high impact of hot-electron spins onto atomic-scale magnets.

Received 30 April 2012

DOI:https://doi.org/10.1103/PhysRevLett.109.097602

Authors & Affiliations

Anika Schlenhoff^*, Stefan Krause, Andreas Sonntag, and Roland Wiesendanger

Institute of Applied Physics and Microstructure Research Center, University of Hamburg, Jungiusstr. 11, 20355 Hamburg, Germany

^*aschlenh@physnet.uni-hamburg.de

Article Text (Subscription Required)

Click to Expand

Supplemental Material (Subscription Required)

Click to Expand

References (Subscription Required)

Click to Expand

Issue

Vol. 109, Iss. 9 — 31 August 2012

Reuse & Permissions

Access Options

Author publication services for translation and copyediting assistance advertisement

Images

Figure 1
Injecting spin-polarized field-emitted electrons into a nanomagnet. (a) Physical picture of resonantly injecting spin-polarized field-emitted electrons for the parallel (left) or antiparallel (right) alignment of tip and sample magnetization. (b) Situation for conventional SP-STM. (c) Sketch of the experimental setup and topography of a Fe/W(110) nanomagnet, textured with a magnetic map. The nanomagnet frequently switches between two states (red and green). The fast scanning direction of the tip is along $x$ . (d) $Δ z (U)$ and $d I / d U (U)$ , revealing the first six field-emission resonances. (e) First FER peak. It changes as the nanomagnet switches its magnetization. $I = 2 nA$ , $T = 38.8 K$ .Reuse & Permissions
Figure 2
Magnetic imaging using spin-polarized field emission. (a) SP-SFEM topography and magnetic map, recorded at $U = 4.6 V$ . Characteristic stripe patterns evolve on the nanomagnets. The fast scanning direction is along $x$ . (b) Zoom to one nanomagnet, imaged with spin-polarized field-emitted electrons (left) and conventional SP-STM (right). The topography line sections show an increase of apparent height and lateral dimension. $I = 2 nA$ , $T = 38.8 K$ . (c) Trace section of the magnetic telegraph noise recorded on the nanomagnet of (b) using SP-SFEM (top) and SP-STM (bottom). $I = 2 nA$ , $T = 39.4 K$ .Reuse & Permissions
Figure 3
Manipulation of the magnetic switching behavior using spin-polarized field-emitted electrons. (a) Mean lifetimes as a function of current (top) and respective lifetime asymmetry (bottom). (b) Temperature increase $Δ T (I)$ of the nanomagnet. (c) Modification $Δ E (I)$ of $E_{b}$ . For comparison, the results using low-energy tunneling electrons on the same nanomagnet are indicated by dashed lines. $U = 4.9, \dots, 5.1 V$ , $T = 35.4 K$ . (d) Spin-flip of electrons: (i) within the FER spin states, generating magnons or (ii) when relaxing from the FER spin state into the sample, resulting in Stoner excitations.Reuse & Permissions
Figure 4
Magnetization reversal triggered by field-emitted electrons. SP-STM topography textured with magnetic map of the sample. (a) Before and (b) after ramping a field-emission current on one individual nanomagnet (marked by arrow). $U = 0.1 V$ , $I = 2 nA$ , $T = 31.5 K$ . (c) $d I / d U (I)$ signal while ramping $I$ on the nanomagnet using field-emitted electrons. A jump is observed at $I = 63 nA$ , indicating magnetization reversal. Red and green lines indicate the $d I / d U$ signal for state $0$ and $1$ , respectively. $U = 5 V$ .Reuse & Permissions

Physical Review Letters