Spin Resolution and Evidence for Superexchange on NiO(001) Observed by Force Microscopy

Abstract

The spin order of the nickel oxide (001) surface is resolved, employing noncontact atomic force microscopy at 4.4 K using bulk Fe and SmCo tips mounted on a qPlus sensor that oscillates at sub-50 pm amplitudes. The spin-dependent signal is hardly detectable with Fe tips. In contrast, SmCo tips yield a height contrast of 1.35 pm for Ni ions with opposite spins. SmCo tips even show a small height contrast on the O atoms of 0.5 pm within the 2×1 spin unit cell, pointing to the observation of superexchange. We attribute the increased signal-to-noise ratio to the increased magnetocrystalline anisotropy energy of SmCo, which stabilizes the magnetic moment at the apex. Atomic force spectroscopy on the Ni↑, Ni↓, and O lattice site reveals a magnitude of the exchange energy of merely 1 meV at the closest accessible distance with an exponential decay length of λexc=18 pm.

Subatomic resolution force microscopy reveals internal structure and adsorption sites of small iron clusters

“…2F were thought to originate from a single atom tip oriented in a [111] direction. We found that COFI images of Fe with its bodycentered-cubic (bcc) structure are similar to COFI images of tungsten (also bcc) [see figure S4 in (39)]. It is easier to evaporate Fe on Cu(111) than W because of its lower melting point.…”

Role of exchange interaction in nitrogen vacancy center based magnetometry

“…Therefore, it is important to explore the full nature of electron-electron interaction, i.e., both the dipole coupling and the exchange coupling, when the NVC is placed in close proximity to the FHM. Recently, the exchange interaction between the ferromagnetic tip and the magnetic sample has also been considered in magnetic exchange force microscopy (MExFM) [42][43][44]. However, to the best of our knowledge, the exchange interaction between proximal NVC spins and FMH spins, has not been considered in NV-based magnetometry.…”

Atomic-resolution single-spin magnetic resonance detection concept based on tunneling force microscopy

“…Applying a similar approach to the spin measurement of individual paramagnetic point defects has been proposed [6,7], yet after more than two decades since the first single-spin detection experiments [8], the spatial resolution of various electrical [9][10][11] , optical [12] and even scanning probe based single spin detection techniques [13][14][15] is one to two orders of magnitude above the localization of the paramagnetic states [8,9,11,13,14]. This limitation makes the application of these spin measurement techniques for a selective readout of adjacent paramagnetic states difficultor, as recently demonstrated, they are based on either scanning tunneling microscopy (STM) [15], spinpolarized scanning tunneling microscopy [16,17] or magnetic exchange force microscopy [17,18,19], all of which employ conductive probe tips, with free carriers that could limit spin coherence times of qubits when the spin readout is used for quantum information applications.…”