Hints for the Control of Magnetic Anisotropy in Molecular Materials

Gatteschi, Dante; Sorace, Lorenzo

doi:10.1006/jssc.2001.9154

Cited by 129 publications

(108 citation statements)

References 56 publications

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“…The d-orbitals of the metal-center are split into the four representations of the group [8]: a 1g (d z 2 ), b 1g (d x 2 −y 2 ), e g (d zx , d yz ), and b 2g (d xy ). Ligand-field models [9] can give the energy levels of the individual orbitals and provide an adequate formalism for describing the ground state and magnetic anisotropy of the individual single molecule magnets [10].…”

Section: Introductionmentioning

confidence: 99%

Mixed configuration ground state in iron(II) phthalocyanine

2015

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We calculate the angular dependence of the x-ray linear and circular dichroism at the L2,3 edges of α-Fe(II) Phthalocyanine (FePc) thin films using a ligand field model with full configuration interaction. We find the best agreement with the experimental spectra for a mixed ground state of 3 Eg(a ) with the two configurations coupled by the spin-orbit interaction. The 3 Eg(b) and 3 B2g states have an easy axis and plane anisotropies, respectively. Our model accounts for an easy-plane magnetic anisotropy and the measured magnitudes of the in-plane orbital and spin moments. The proximity in energy of the two configurations allows a switching of the magnetic anisotropy from easy plane to easy axis with a small change in the crystal field, as recently observed for FePc adsorbed on an oxidized Cu surface. We also discuss the possibility of a quintet ground state ( 5 A1g is 250 meV above the ground state) with planar anisotropy by manipulation of the Fe-C bond length by depositing the complex on a substrate that is subjected to a mechanical strain.

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Section: Introductionmentioning

confidence: 99%

Mixed configuration ground state in iron(II) phthalocyanine

2015

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“…We extract the effective switching rate between the high-spin ground states via all possible spin paths, as experimentally manifested in two-state telegraph noise, utilizing a master equation approach. With comparative analysis we show how a single spin on two-, three-and fourfold symmetric substrates [15] responds to temperature, external magnetic field, as well as inelastic tunneling electrons. Higher symmetries are not part of our discussion since they are difficult to realize experimentally.…”

mentioning

confidence: 99%

Symmetry effects on the spin switching of adatoms

Hübner¹,

Baxevanis

Khajetoorians

et al. 2014

Phys. Rev. B

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Highly symmetric magnetic environments have been suggested to stabilize the magnetic information stored in magnetic adatoms on a surface. Utilized as memory devices such systems are subjected to electron tunneling and external magnetic fields. We analyze theoretically how such perturbations affect the switching probability of a single quantum spin for two characteristic symmetries encountered in recent experiments and suggest a third one that exhibits robust protection against surface-induced spin flips. Further we illuminate how the switching of an adatom spin exhibits characteristic behavior with respect to low energy excitations from which the symmetry of the system can be inferred. Recently, single magnetic atoms on surfaces, or so-called magnetic adatoms, have gained a lot of interest for spin-based information storage and processing [1][2][3]. These concepts are mostly based on strong magnetic anisotropy energy [4,5], which reduces spin degeneracy at zero magnetic field, thereby defining preferential spatial orientations of the spin. While magnetic anisotropy introduces an energy cost for magnetization reversal, countless studies have illustrated that in the presence of strong magnetic anisotropy, individual magnetic adatoms still exhibit rather short lifetimes [6][7][8] owing to the interplay of the hybridization of the moment bearing orbitals and the underlying substrate. Such observations question the role of both tunneling electrons as well as substrate electrons in dynamical processes of the atomic spin [5,[9][10][11][12][13]. In order to enhance the dynamic stability of such adatoms, strong magnetic coupling between individual spins can be utilized to protect the total spin from fluctuations [2,14].A different approach, that stabilizes a single magnetic moment of an adatom, was utilized by a particular choice of both spin and underlying substrate symmetry [3]. In particular for a threefold symmetric system with the net magnetic moment S = 8 of a holmium adatom, it is possible to protect the spin, in the absence of perturbations, from single-electroninduced spin reversal. It is yet unknown how perturbations, like current-based read out or static magnetic fields which break the symmetry of the system, effect the symmetry caused stability of the spin in such quantum systems.Here we approach this question with a focus on the prospects of using a specific symmetry to protect a spin from switching. We extract the effective switching rate between the high-spin ground states via all possible spin paths, as experimentally manifested in two-state telegraph noise, utilizing a master equation approach. With comparative analysis we show how a single spin on two-, three-and fourfold symmetric substrates [15] responds to temperature, external magnetic field, as well as inelastic tunneling electrons. Higher symmetries are not part of our discussion since they are difficult to realize experimentally. We find that the threeand fourfold symmetric systems are both protected against single-electron-induced ground state s...

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“…This situation is the one most often encountered in practice [in this case eqs. (21) and (22) simplify: k r and k u are replaced by 2, s r and s u by s, and remaining indices r,u can be dropped]. The tensors Λ s can be parameterized as usual by D s and E s parameters, and the non-zero components of the corresponding spherical tensors become T (21) is obtained asĤ…”

Section: Effective Spin Hamiltonian*mentioning

confidence: 99%

Many-spin effects in inelastic neutron scattering and electron paramagnetic resonance of molecular nanomagnets

Waldmann

Güdel

2005

Phys. Rev. B

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Many molecular magnetic clusters, such as single-molecule magnets, are characterized by spin ground states with defined total spin S exhibiting zero-field-splittings. In this work, the spectroscopic intensities of the transitions within the ground-state multiplet are analyzed. In particular, the effects of a mixing with higher-lying spin multiplets, which is produced by anisotropic interactions and is neglected in the standard single-spin description, are investigated systematically for the two experimental techniques of inelastic neutron scattering (INS) and electron paramagnetic resonance (EPR), with emphasis on the former technique. The spectroscopic transition intensities are calculated analytically by constructing corresponding effective spin operators perturbationally up to second order and consequently using irreducible tensor operator techniques. Three main effects of spin mixing are observed. Firstly, a pronounced dependence of the INS intensities on the momentum transfer Q, with a typical oscillatory behavior, emerges in first order, signaling the many-spin nature of the wave functions in exchange-coupled clusters. Secondly, as compared to the results of a first-order calculation, the intensities of the transitions within the spin multiplet are affected differently by spin mixing. This allows one, thirdly, to differentiate the higher-order contributions to the cluster magnetic anisotropy which come from the single-ion ligand-field terms and spin mixing, respectively. The analytical results are illustrated by means of the three examples of an antiferromagnetic heteronuclear dimer, the Mn-[3 × 3] grid molecule, and the single-molecule magnet Mn12.

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Hints for the Control of Magnetic Anisotropy in Molecular Materials

Cited by 129 publications

References 56 publications

Mixed configuration ground state in iron(II) phthalocyanine

Mixed configuration ground state in iron(II) phthalocyanine

Symmetry effects on the spin switching of adatoms

Many-spin effects in inelastic neutron scattering and electron paramagnetic resonance of molecular nanomagnets

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