Erratic magnetic hysteresis of TbPc2 molecular nanomagnets

Malavolti, Luigi; Mannini, Matteo; Car, Pierre‐Emmanuel; Campo, Giulio; Pineider, Francesco; Sessoli, Roberta

doi:10.1039/c3tc00925d

Cited by 66 publications

(81 citation statements)

References 50 publications

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“…On the contrary, our data on TbPc 2 multilayers on MgO reveal that vertical interactions accelerate magnetization relaxation. [ 20,21 ] In summary, we have demonstrated that MgO thin fi lms realize the combination of effi cient protection from electron scattering and weak molecule-surface hybridization to achieve optimal properties of SMMs on electrode surfaces. In addition, in the present case of TbPc 2 the molecules are self-assembled into well-ordered islands leading to highly uniform molecular ensembles with out-of-plane easy axes.…”

Section: Communicationmentioning

confidence: 84%

“…We use nonmagnetic, insulating MgO, wellknown in inorganic spintronic applications, [ 17,18 ] which allows to control the electron tunneling rate over many orders of magnitude. [ 19 ] Moreover, we employ the TbPc 2 SMM [ 14,15,[20][21][22][23] as a model system. In the neutral molecule, the Tb(III) ion exhibits an electronic spin state of J = 6.…”

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confidence: 99%

“…[ 21,22 ] Symmetry breaking enables mixing terms in the TbPc 2 spin Hamiltonian that, together with the hyperfi ne interaction, promotes quantum tunneling of magnetization especially around zero fi eld. [ 4,5,21,22 ] Owing to the low hybridization on MgO the upper and lower Pc ligands retain the same electronic structure as in the gas phase, preserving the molecular D 4d symmetry nearly perfectly. By contrast, upon direct adsorption onto metal surfaces the electronic structure of the lower Pc ligand in contact with the surface is slightly altered because of adsorption bonds and molecule-surface charge transfer, reducing the symmetry of the Tb ligand fi eld to C 4v or lower.…”

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confidence: 99%

“…This is attributed to magnetic interactions between the molecules. [ 21 ] In addition to MgO, we also investigated hexagonal boron nitride ( h -BN) [ 28 ] as a tunnel barrier. The hysteresis opening on h -BN is wider than the one reported for most surface-adsorbed TbPc 2 (Supporting Information), however, it is signifi cantly narrower than on the MgO thin fi lm.…”

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Giant Hysteresis of Single‐Molecule Magnets Adsorbed on a Nonmagnetic Insulator

et al. 2016

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metal electrode. We use nonmagnetic, insulating MgO, wellknown in inorganic spintronic applications, [ 17,18 ] which allows to control the electron tunneling rate over many orders of magnitude. [ 19 ] Moreover, we employ the TbPc 2 SMM [ 14,15,[20][21][22][23] as a model system. In the neutral molecule, the Tb(III) ion exhibits an electronic spin state of J = 6. It is sandwiched between two phthalocyanine (Pc) macrocycles (cf. schematic view in Figure 1 a) hosting an unpaired electron delocalized over the Pc ligands. The easy-axis-type magnetic anisotropy imposes an energy barrier of ≈65 meV for magnetization reversal, [ 23 ] which is largest within the whole series of lanthanide-Pc 2 SMMs. [ 14,15 ] On nonmagnetic conducting substrates, only vanishing remanence [6][7][8][9][10] and very narrow hysteresis loops [6][7][8][9] were observed, much smaller than in bulk measurements, [ 20 ] illustrating the disruptive effects of the surface. We note that the adsorption of TbPc 2 on (anti)ferromagnetic materials represents a different situation because of the magnetic exchange interaction with the substrate. [ 24,25 ] In those cases, the SMMs were not shown to exhibit slow relaxation of magnetization. Rather, the hysteresis is linked to the one of the magnetic substrates, i.e., it is not an intrinsic property of the SMMs. Overall, the detailed knowledge on TbPc 2 makes it an ideal candidate to test if a tunnel barrier can boost the magnetic properties of surface-adsorbed SMMs. In this communication we show that the magnetic remanence and hysteresis opening obtained with TbPc 2 on MgO tunnel barriers outperform the ones of any other surface-adsorbed SMM [4][5][6][7][8][9][10][11][12][13]26 ] as well as those of bulk samples of TbPc 2 . [ 20 ] The scanning tunneling microscopy (STM) images in Figure 1 b,c show that TbPc 2 self-assembles by forming perfectly ordered 2D islands on two monolayers (MLs) of MgO on Ag(100). In line with former results, the SMMs are adsorbed fl at on the surface (cf. discussion of our STM and X-ray linear dichroism (XLD) data below). [ 6,27 ] This excludes that the extraordinary magnetic properties observed in this study are due to upstanding molecules having their macrocycles perpendicular to the surface, which would lead to a reduced interaction of the Tb(III) ion with the surface. The high-resolution image in Figure 1 c reveals eight lobes per molecule, reminiscent of the staggered conformation of the two phthalocyanine ligands. [ 27 ] Islands with the identical molecular assembly are formed by TbPc 2 adsorbed directly onto Ag(100), as shown in the Supporting Information.The magnetic properties of the Tb(III) ions in the surfaceadsorbed SMMs are determined by X-ray magnetic circular dichroism (XMCD) measurements at the M 4,5 (3 d → 4 f ) edges of Tb. For sub-MLs of TbPc 2 on MgO we fi nd a strong remanence larger than 40% of the saturation magnetization sat M and Single-molecule magnets (SMMs) [ 1 ] are very promising for molecular spintronics [ 2 ] and quantum information processing, [...

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