Correlation-Mediated Processes for Electron-Induced Switching between Néel States of Fe Antiferromagnetic Chains

Abstract

The controlled switching between two quasistable Néel states in adsorbed antiferromagnetic Fe chains has recently been achieved by Loth et al. [Science 335, 196 (2012)] using tunneling electrons from an STM tip. In order to rationalize their data, we evaluate the rate of tunneling electron-induced switching between the Néel states. Good agreement is found with the experiment, permitting us to identify three switching mechanisms: (i) The search for nanoscale electronic devices has prompted intense research in the field of nanomagnetism. The use of spin as the information conveying entity has stirred much excitement due to its extraordinary properties of information storage, speed, and low-energy consumption [1][2][3]. Miniaturization is quickly proceeding, reaching very small domain-wall devices [4], atomic-size devices [5], and the realm of molecular devices [2,[6][7][8][9]. Among all these possibilities, antiferromagnetically (AFM) coupled devices have recently received a lot of attention. The AFM characteristics make these devices very well fitted for quantum computation since they naturally involved entangled states [10,11]. Moreover, the storage in AFM devices is particularly robust due to the lack of a total magnetic moment. However, this robustness has deterred their use because changing their magnetic state becomes difficult [12].Recently, Loth and co-workers succeeded in controllably switching the spin states of AFM atomic chains [12]. Two quasistable Néel states, exhibiting alternating spin directions on the atoms along the chain, were evidenced in Fe chains adsorbed on a CuN=Cuð100Þ surface. Loth and co-workers showed that the Néel states can be switched by tunneling electrons injected from a polarized scanning tunneling microscope (STM) tip into one of the atoms of the chain. This demonstrated the possibility of storing information on the atomic-scale antiferromagnet. Theoretical predictions show that writing and reading spin states entail fundamental problems associated with the quantum nature of the process [13]. Spin manipulation by tunneling electrons has been pictured as due to a spintorque mechanism where spin angular momentum from the electron is transferred into the atomic spin system [14][15][16]. However, due to the lack of magnetic moment in AFM systems, spin manipulation must follow a different mechanism. Unavoidably, spin manipulations and excitations are closely related [17]. Indeed, switching between Néel states has been experimentally associated with overcoming an activation energy [12]. However, in the case of degenerate Néel states, resonant transitions should be expected. Hence, the experimental data raise many questions regarding the possibility of resonant switching, the efficiency of activated switching, the nature of the involved excitations, and the physics at play in AFM spin torque. In summary, a complete view of the switching process is missing.In this Letter, we reveal the switching mechanisms at play in the experiment of Ref. [12]. The mechanisms turn out to be rich and ...

Spin-polarised edge states in atomic Mn chains supported on Cu2N/Cu (100)

“…This is contrary to the case of antiferromagnetic Fe chains where Néel states are revealed by spin-polarised STM [5]. Indeed, the small magnetic anisotropy of Mn chains leads to very entangled spin structures different from the Fe chains [17,32].…”

Structural and magnetic properties ofFeMnxchains(x=1–6)supported onCu2Choi1, Robles2, Gauyacq3 et al. 2016Phys. Rev. BSelf Cite171150View full textAdd to dashboardCite

“…[11][12][13][14][15][16] Fe chains are also well known both experimentally and theoretically. 4,5,15,[17][18][19][20][21] . The work by Lin and Jones 13,22 on Fe, Co and Mn atoms on Cu 2 N/Cu (100) reveals that atomic spins maintain their nominal values on the surface (S F e = 2, S M n =5/2 and S Co = 3/2), showing the interest of using Cu 2 N to preserve much of the magnetic identity of transition-metal (TM) atoms.…”

Dynamical Negative Differential Resistance in Antiferromagnetically Coupled Few-Atom Spin Chains

“…where n i (t) is the average occupation of each spin state and r ij is the transition rate from whereˆ S is the vector spin operator of the magnetic atom with which the electron interacts,ˆ σ is the vector spin operator of the tunneling electron andÎ is the identity operator accounting for spin-independent scattering with strength u. This scattering Hamiltonian was previously found to quantitatively account for elastic and inelastic electron tunneling at magnetic atoms and molecules [18,[42][43][44][45][46][47][48][49][50]. To first order, the transiton rates are given by the product of this operator's transition matrix elements between the spin states of Fe trimer |i and |j [24].…”