Model of orbital populations for voltage-controlled magnetic anisotropy in transition-metal thin films

Zhang, Jia; Lukashev, Pavel; Jaswal, S. S.; Tsymbal, Evgeny Y.

doi:10.1103/physrevb.96.014435

Cited by 88 publications

(79 citation statements)

References 46 publications

(49 reference statements)

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“…Here, E soc =<¯h L and S are orbital and spin operators, respectively. The expectation value of E soc is twice the actual value of the total energy correction to the second-order in SOC, i.e., MAE ≈ 1/2∆E soc [45,50]. Our test calculations indicate that the second-order perturbation theory is a reasonable approximation as the total MAE overall agree within a few percent accuracy with those obtained from the atom and orbital projected calculations.…”

Section: Resultssupporting

confidence: 52%

“…To anticipate this phenomenon, we have performed electrostatic doping calculations by changing the number of valence electrons (n e ) in the whole system (4×4 unit cell of ZnO monolayer) from n e = −1.5 to +1.5e − . This approach reflects to the charge carrier density that is confined over the metallic surface rather than exceeding to a vacuum region, which is analogues to the electric field effect by the positive and negative gating as well as chemical doping with the neighboring elements (e.g., Cu or Ga for Zn, and N or F for O site) [50].…”

Section: Resultsmentioning

confidence: 99%

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Inducing and manipulating magnetization in 2D zinc–oxide by strain and external voltage

Taivansaikhan¹,

Tsevelmaa²,

Rhim³

et al. 2018

J. Phys.: Condens. Matter

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Two-dimensional (2D) structures that exhibit intriguing magnetic phenomena such as perpendicular magnetic anisotropy and its switchable feature are of great interests in spintronics research. Herein, the density functional theory studies reveal the critical impacts of strain and external gating on vacancy-induced magnetism and its spin direction in a graphene-like single layer of zinc oxide (ZnO). In contrast to the pristine and defective ZnO with an O-vacancy, the presence of a Zn-vacancy induces significant magnetic moments to its first neighboring O and Zn atoms due to the charge deficit. We further predict that the direction of magnetization easy axis reverses from an in-plane to perpendicular orientation under a practically achievable biaxial compressive strain of only ~1-2% or applying an electric field by means of the charge density modulation. This magnetization reversal is mainly driven by the strain- and electric-field-induced changes in the spin-orbit coupled d states of the first-neighbor Zn atom to a Zn-vacancy. These findings open interesting prospects for exploiting strain and electric field engineering to manipulate magnetism and magnetization orientation of 2D materials.

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Section: Resultssupporting

confidence: 52%

Section: Resultsmentioning

confidence: 99%

Inducing and manipulating magnetization in 2D zinc–oxide by strain and external voltage

Taivansaikhan¹,

Tsevelmaa²,

Rhim³

et al. 2018

J. Phys.: Condens. Matter

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show abstract

“…13 To date there are two major bottlenecks in optimizing the performance of MeRAM devices: (1) Large perpendicular magnetic anisotropy (PMA) (higher than 2 erg/cm 2 ) to ensure the stability of the magnetic bit at room temperature; and (2) High VCMA efficiency (β ≥ 1,000 fJ/Vm) in order to replace DRAM at 7 nm node. 14,15 In recent years intense experimental 8,11,12,[15][16][17] and theoretical 9,10,[18][19][20][21][22][23] efforts have focused on understanding the possible mechanisms that govern the VCMA and identifying materials to achieve both high PMA and VCMA efficiency. Nevertheless, experimental works in Ta/Co 40 F e 40 B 20 /MgO 16,24 , Au/FeCo/MgO 25 , and Irdoped Fe/MgO 26 have reported overall rather limited values of PMA (< 2 erg/cm 2 ) and VCMA (100-300 fJ/Vm) efficiency.…”

Section: Introductionmentioning

confidence: 99%

Colossal electric field control of magnetic anisotropy at ferromagnetic interfaces induced by iridium overlayer

et al. 2019

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Voltage-induced magnetization switching can lead to a new paradigm enabling ultralow-power and high density instant-on nonvolatile magnetoelectric random access memory (MeRAM) devices. Two major challenges for future MeRAM devices are to achieve large perpendicular magnetic anisotropy (PMA) and high voltage-controlled magnetic anisotropy (VCMA) coefficient of heavymetal/ferromagnet/insulator heterostructures (HM/FM/I). Employing ab initio electronic structure calculations we have investigated the effect of epitaxial strain and thickness of both FeCo and Ir layers as design parameters to optimize the PMA and VCMA of Ir/FeCo/MgO. We predict that the Ir cap layer can induce both large PMA and colossal VCMA efficiency which depend on the stain. More importantly, we predict that a single Ir cap monolayer gives rise to a VCMA efficiency one order of magnitude higher than that of thicker Ir layers. The underlying mechanism is the synergistic effects of the emergence of Ir local moments, the large Ir spin orbit coupling (SOC), and the large modulation of the magnetic anisotropy at the Ir/vacuum interface. These results provide useful guiding rules in the design of the next-generation of high performance MeRAM memory devices.

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“…Furthermore, we can see that the MAEs change rapidly near the E F for (Pb 2 /Fe 1 /) 2 /Pb and (Pb 2 /Fe 1 /) 3 /Pb, which is associated with the significant change of the electron occupancies on the orbitals near the E F . [38,42] Therefore, if the E F can be controlled to shift upwards or downwards, then the MAEs will be reduced or enhanced. Usually, this can be achieved by applying external electric field or injecting charge.…”

Section: Resultsmentioning

confidence: 99%

Large Perpendicular Magnetocrystalline Anisotropy at the Fe/Pb(001) Interface

2018

ACS Appl. Mater. Interfaces

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The search for ultrathin magnetic films with large perpendicular magnetocrystalline anisotropy (PMA) has been inspired for years by the continuous miniaturization of magnetic units in spintronics devices. The common magnetic materials used in research and applications are based on Fe because the pure Fe metal is the best yet simple magnetic material from nature. Through systematic first-principles calculations, we explored the possibility to produce large PMA with ultrathin Fe on non-noble and non-magnetic Pb(001) substrate. Interestingly, huge magnetocrystalline anisotropy energy (MAE) of 7.6 meV was found in the Pb/Fe/Pb(001) sandwich structure with only half monolayer Fe. The analysis of electronic structures reveals that the magnetic proximity effect at the interface is responsible for this significant enhancement of MAE. The MAE further increases to 13.6 meV with triply repeated capping Pb and intermediate Fe layers. Furthermore, the MAE can be tuned conveniently by charge injection.

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Model of orbital populations for voltage-controlled magnetic anisotropy in transition-metal thin films

Cited by 88 publications

References 46 publications

Inducing and manipulating magnetization in 2D zinc–oxide by strain and external voltage

Inducing and manipulating magnetization in 2D zinc–oxide by strain and external voltage

Colossal electric field control of magnetic anisotropy at ferromagnetic interfaces induced by iridium overlayer

Large Perpendicular Magnetocrystalline Anisotropy at the Fe/Pb(001) Interface

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