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SUPPLEMENTARY INFORMATIONDOI: 10.1038/NMAT4361

NATURE MATERIALS | www.nature.com/naturematerials 1

Exchange bias and room temperature magnetic orderin molecular layers

Manuel Gruber1,2, Fatima Ibrahim1, Samy Boukari1, Hironari Isshiki2, Loïc Joly1,Moritz Peter2, Michał Studniarek1,3, Victor Da Costa1, Hashim Jabbar1, VincentDavesne1,2, Ufuk Halisdemir1, Jinjie Chen2, Jacek Arabski1, Edwige Otero3, FadiChoueikani3, Kai Chen3, Philippe Ohresser3, Wulf Wulfhekel2,4, Fabrice Scheurer1,Wolfgang Weber1, Mebarek Alouani1, Eric Beaurepaire1 & Martin Bowen1

1 Institut de Physique et Chimie des Matériaux de Strasbourg, Université de Strasbourg,CNRS UMR 7504, 23 rue du Loess, BP 43, F-67034 Strasbourg Cedex 2, France2 Physikalisches Institut, Karlsruhe Institute of Technology, Wolfgang-Gaede-Str. 1, 76131Karlsruhe, Germany3 Synchrotron SOLEIL,L’Orme des Merisiers, Saint-Aubin - BP 48, 91192 Gif-sur-Yvette,France4 Institute of Nanotechnology, Karlsruhe Institute of Technology, 76021 Karlsruhe, Ger-many

Exchange bias and room-temperature magnetic order in molecular layers

© 2015 Macmillan Publishers Limited. All rights reserved

http://dx.doi.org/10.1038/nmat4361

2 NATURE MATERIALS | www.nature.com/naturematerials

SUPPLEMENTARY INFORMATION DOI: 10.1038/NMAT4361

1 Thickness-dependent orientation of molecules relative tothe Co substrate

We detail in this section how we use x-ray natural linear dichroism (XNLD) of x-rayabsorption spectroscopy (XAS) to determine the orientation of MnPc molecules28 as afunction of film thickness when deposited onto Co(100). In our experimental geometry,the Co(100) film is positioned vertically so as to intersect the horizontal x-ray beam (seeFig. S1 a). By rotating the sample about a vertical axis, one may thus achieve either normalor grazing x-ray incidence. In the present geometry, the x-ray beam makes an angle of 40◦

with the surface of the sample. Thus, for linear vertical (LV) polarization the electric fieldoscillates within the sample’s plane, whereas for linear horizontal (LH) polarization theelectric field has components both in and out of plane (Fig. S1a). Absorption is promotedwithin unoccupied orbitals that are spatially oriented parallel to the electric field.

MnPc molecules are, to first approximation,29 two-dimensional. The unoccupied σ∗

(π∗) orbitals of the nitrogren sites in MnPc are directed in (out of) the molecule’s plane.If the molecules have the same orientation, the orbital anisotropy can be maintained andrevealed by XNLD. Thus, in our experimental geometry, the molecules lying flat on theunderlying substrate lead to a higher efficiency of the transition into the π∗ (σ∗) unoccupiedstate for linear horizontal (vertical) x-ray polarization (see Fig S1a).30–33

The XAS spectra for linear horizontal (LH) and linear vertical (LV) x-ray polarizationsshown in Fig. S1b, measured on a sample of 3.5 ML MnPc on Cu(100)//Co indicatethat the π∗ (σ∗) orbitals of the nitrogen atoms are mainly perpendicular (parallel) tothe surface, revealing a mostly flat adsorption of the molecule onto the surface. LV andLH XAS spectra for three different MnPc thicknesses exhibit strong linear dichroism (seeFig S1c) that is indicative of a preferred flat absorption of the molecule onto the Co surface.

To more quantitatively determine the proportion of molecules that lie within the sub-strate plane, we extracted the XNLD intensity for each MnPc thickness and normalized itto that found for 0.7 ML (see Fig S1d). We justify this normalization as follows. As wedescribe in the main manuscript, the presence of strong Mn coupling to the Co substrate,the nearly identical shape of the Mn and Co hysteresis loops, and the absence of indicationsof Mn paramagnetism for this coverage, all indicates that the first-ML molecules lie flatonto the Co substrate. It is therefore against this reference that we compare the XNLDamplitude for higher coverages.

The XNLD amplitude decreases only slightly when going from 0.7 ML to 1.9 ML.This indicates that almost all second-ML MnPc molecules lie flat. At a MnPc coverageof 3.5 ML, the XNLD intensity is decreased by about 30% compared to that found for0.7 ML. The loss in XNLD intensity at 3.5 ML is due to a proportion of molecules thatdoes not lie flat onto the Co surface. We infer that this proportion of MnPc moleculesin turn accounts for the partial paramagnetic signal observed in the magnetic hysteresisloop (see Fig. 2b of the manuscript). We note that, due to the angle of 40◦ instead of 0◦

between the photon-incidence vector and the surface, the amplitude of the linear dichroismshown in Figs. S1b and S1c is limited.

XNLD results give us information about the angle between the molecular plane and thesurface, i.e. whether the molecules have a tendency to lie flat or vertically on the surface.To gain further insight into the adsorption geometry of the molecules, we performed scan-ning tunneling microscopy (STM) experiments. In Fig. S2a we show a STM topographyof low MnPc coverage on Cu(100)//Co(10ML). Note that the Cu(100)//Co(10ML) wasannealed to 100 ◦C for 10 min. Molecules were then deposited onto the substrate held atroom temperature.

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T = 295 KT = 295 K

Figure S1: XNLD as a function of molecular coverage. a, Schematic view of a MnPcmolecule lying flat on the Co substrate where iso-density of nitrogen π∗ orbitals are rep-resented in green for clarity. For incoming x-rays at an angle of 40◦ to the surface, theefficiency of the core-state to π∗-state absorption is higher if the electric field oscillates par-allel to the unoccupied π∗ orbitals (linear horizontal polarization represented in blue). Thelinear vertical polarization (represented in red) is more efficient to probe core-state to σ∗-state transitions that require higher photon energy than core-state to π∗-state transitions.b, XAS performed at the nitrogen K edge (1s to 2p transitions) at a MnPc thickness of3.5 ML at RT for two different linear polarizations of the photons. The absorption comingfrom π∗ (σ∗) orbitals is higher for linear horizontal (vertical) polarization of the photonsrevealing a mostly flat absorption of the molecules on the cobalt surface. c, XAS at thenitrogen K edge normalized by the white line intensity at 402.3 eV for MnPc coverages of0.7 ML, 2.2 ML and 3.5 ML. d, Normalized XNLD as a function of MnPc coverage. Thenormalization procedure is done by calculating LH−LV

(LH+LV )/2 at 402.3 eV, and then dividingby the XNLD found for 0.7 ML.





1 Thickness-dependent orientation of molecules relative tothe Co substrate

We detail in this section how we use x-ray natural linear dichroism (XNLD) of x-rayabsorption spectroscopy (XAS) to determine the orientation of MnPc molecules28 as afunction of film thickness when deposited onto Co(100). In our experimental geometry,the Co(100) film is positioned vertically so as to intersect the horizontal x-ray beam (seeFig. S1 a). By rotating the sample about a vertical axis, one may thus achieve either normalor grazing x-ray incidence. In the present geometry, the x-ray beam makes an angle of 40◦

with the surface of the sample. Thus, for linear vertical (LV) polarization the electric fieldoscillates within the sample’s plane, whereas for linear horizontal (LH) polarization theelectric field has components both in and out of plane (Fig. S1a). Absorption is promotedwithin unoccupied orbitals that are spatially oriented parallel to the electric field.

MnPc molecules are, to first approximation,29 two-dimensional. The unoccupied σ∗

(π∗) orbitals of the nitrogren sites in MnPc are directed in (out of) the molecule’s plane.If the molecules have the same orientation, the orbital anisotropy can be maintained andrevealed by XNLD. Thus, in our experimental geometry, the molecules lying flat on theunderlying substrate lead to a higher efficiency of the transition into the π∗ (σ∗) unoccupiedstate for linear horizontal (vertical) x-ray polarization (see Fig S1a).30–33

The XAS spectra for linear horizontal (LH) and linear vertical (LV) x-ray polarizationsshown in Fig. S1b, measured on a sample of 3.5 ML MnPc on Cu(100)//Co indicatethat the π∗ (σ∗) orbitals of the nitrogen atoms are mainly perpendicular (parallel) tothe surface, revealing a mostly flat adsorption of the molecule onto the surface. LV andLH XAS spectra for three different MnPc thicknesses exhibit strong linear dichroism (seeFig S1c) that is indicative of a preferred flat absorption of the molecule onto the Co surface.

To more quantitatively determine the proportion of molecules that lie within the sub-strate plane, we extracted the XNLD intensity for each MnPc thickness and normalized itto that found for 0.7 ML (see Fig S1d). We justify this normalization as follows. As wedescribe in the main manuscript, the presence of strong Mn coupling to the Co substrate,the nearly identical shape of the Mn and Co hysteresis loops, and the absence of indicationsof Mn paramagnetism for this coverage, all indicates that the first-ML molecules lie flatonto the Co substrate. It is therefore against this reference that we compare the XNLDamplitude for higher coverages.

The XNLD amplitude decreases only slightly when going from 0.7 ML to 1.9 ML.This indicates that almost all second-ML MnPc molecules lie flat. At a MnPc coverageof 3.5 ML, the XNLD intensity is decreased by about 30% compared to that found for0.7 ML. The loss in XNLD intensity at 3.5 ML is due to a proportion of molecules thatdoes not lie flat onto the Co surface. We infer that this proportion of MnPc moleculesin turn accounts for the partial paramagnetic signal observed in the magnetic hysteresisloop (see Fig. 2b of the manuscript). We note that, due to the angle of 40◦ instead of 0◦

between the photon-incidence vector and the surface, the amplitude of the linear dichroismshown in Figs. S1b and S1c is limited.

XNLD results give us information about the angle between the molecular plane and thesurface, i.e. whether the molecules have a tendency to lie flat or vertically on the surface.To gain further insight into the adsorption geometry of the molecules, we performed scan-ning tunneling microscopy (STM) experiments. In Fig. S2a we show a STM topographyof low MnPc coverage on Cu(100)//Co(10ML). Note that the Cu(100)//Co(10ML) wasannealed to 100 ◦C for 10 min. Molecules were then deposited onto the substrate held atroom temperature.

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ts)

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mal

ized

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LD (

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T = 295 K

T = 295 KT = 295 K

Figure S1: XNLD as a function of molecular coverage. a, Schematic view of a MnPcmolecule lying flat on the Co substrate where iso-density of nitrogen π∗ orbitals are rep-resented in green for clarity. For incoming x-rays at an angle of 40◦ to the surface, theefficiency of the core-state to π∗-state absorption is higher if the electric field oscillates par-allel to the unoccupied π∗ orbitals (linear horizontal polarization represented in blue). Thelinear vertical polarization (represented in red) is more efficient to probe core-state to σ∗-state transitions that require higher photon energy than core-state to π∗-state transitions.b, XAS performed at the nitrogen K edge (1s to 2p transitions) at a MnPc thickness of3.5 ML at RT for two different linear polarizations of the photons. The absorption comingfrom π∗ (σ∗) orbitals is higher for linear horizontal (vertical) polarization of the photonsrevealing a mostly flat absorption of the molecules on the cobalt surface. c, XAS at thenitrogen K edge normalized by the white line intensity at 402.3 eV for MnPc coverages of0.7 ML, 2.2 ML and 3.5 ML. d, Normalized XNLD as a function of MnPc coverage. Thenormalization procedure is done by calculating LH−LV

(LH+LV )/2 at 402.3 eV, and then dividingby the XNLD found for 0.7 ML.





We can clearly observe the four-fold symmetry of the molecules. This independentlyconfirms that the first-ML molecules lie flat on the Co(100) surface. This is in agree-ment with similar STM studies of different metal Phthalocyanine molecules on differentsurfaces.31,34–39

When the MnPc coverage is further increased, we can observe first- and second-MLMnPc molecules in the same STM topography (see Fig. S2b). First- and second-MLmolecules both exhibit a four-fold symmetry, implying that both adsorb flat on the surface.Moreover, while first-ML molecules appear with 4 lobes with a cross-like shape, second-MLmolecules reveal a more complicated structure coming from the molecular orbitals with anoverall cross shape (see zoomed images in Fig. S2a and b). This behavior has been similarlyobserved in other Pc-based systems, e.g. FePc40 and YPc2

41 on Au(111). The complexstructure is attributed to the molecular orbitals of the second-ML MnPc molecules thatare decoupled from the substrate by the first-ML MnPc molecules.

We then used different STM topographies to extract the in-plane orientation of themolecules relative to the [011] crystallographic orientation of the fcc Cu(100)//Co(10ML)substrate. We proceeded as follows: (i) we distinguished first- and second-ML molecules.(ii) We marked the molecules with a cross where the two axes of the cross represent themirror symmetry of the marked molecule. Two examples with higher magnification areshown in the inserts of Fig. S2a and b. Note that the molecules have a four-fold symmetryand thus the two axes of a given cross are equivalent. (iii) The shortest positive anglebetween an axis of the cross and the crystallographic [011] direction is measured for everymolecule. (iv) Histograms of the angles’ distribution are generated for first- (see Fig. S2c)and second-ML (see Fig. S2d) MnPc molecules. According to the histogram for first-MLMnPc molecules, the first-ML molecules have two preferential in-plane orientations: ≈30◦

and ≈60◦ relative to the [011] crystallographic axis (see Fig. S2c). The angles exhibit adistribution with a width of ±6◦. Note that the [011] and [011] crystallographic axes areequivalent. The molecules with angle of 30◦ relative to the [011] axis make an angle of 60◦

with the [011] axis. Yet, second-ML MnPc molecules have the same in-plane orientations asfirst-ML molecules, i.e. ≈30◦ and ≈60◦ relative to the [011] crystallographic axis (see Fig.S2d). Now, by combining the results of the histograms of the angle for first- and second-ML molecules (see Fig. S2c-d), we can consider the in-plane orientation of a second-MLmolecule relative to the in-plane orientation of the first-ML molecule. Since the angledistribution are similar for first- and second-ML molecules (see Fig. S2c-d), a second-MLmolecule has an in-plane orientation that is either i) identical to, or ii) rotated by ≈30◦

relative to, that of the first-ML molecule. STM topographies cannot distinguish betweenthese two scenarii. Note also that from our measurements, we cannot extract the positionof the Mn ion within the second-ML molecule relative to that of the first-ML molecule.

ba c

1st layer

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5

10

15

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Figure S2: STM experiments on two samples with different coverages. a, STMtopography of Cu(100)//Co(10ML) with low coverage of MnPc. We superimposed bluecrosses over molecules to extract the molecules’ orientation relative to the [011] crystallo-graphic axis. We provide a zoom on one molecule to illustrate the orientation. b, STMtopography of higher MnPc coverage on Cu(100)//Co(10ML). Blue (red) crosses indicatethe orientation of first(second)-ML MnPc molecules. We provide a zoom on a second-layer molecule to illustrate the orientation and the different appearance of second-MLmolecules. Histograms of the orientation of the molecules for c first- and d second-MLMnPc molecules. The histograms were built by taking, for each molecule, the shortestpositive angle between an axis of the molecule and the [011] crystallographic axis. Imagessizes are a, 12 × 12 nm2 (V = 1.0V,I = 50 pA) and b, 12 × 12 nm2 (V = 1.0V,I = 100pA). The histograms c and d were realized using topographies of high coverage MnPc suchas in b and with statistic of 41 and 56 molecules, respectively.





2 Electronic structure of Mn site within first- and second-MLMnPc molecules

We discuss in this Section differences in electronic structure between first-ML MnPcmolecules that form the spinterface with Co, and second-ML molecules that are adsorbedonto first-ML molecules. To do so, we examine in Fig. S3a-b the XAS at the Mn L3,2 edgesfor left and right photon helicities that were used to determine the XMCD spectra shownin Fig. 2a of the manuscript. We present in Fig. S3c-d the white line spectra correspond-ing to the average of left and right photon-helicity spectra. We see that the shape of theL3 edge is modified when going from 0.7 ML to 1.9 ML. Indeed, the main peak initiallypositioned at 648.5 eV for a molecular coverage of 0.7 ML is shifted towards a lower energyof 647.1 eV for a coverage of 1.9 ML or higher. This shift in peak position arises from astrong (weak) hybridization of the first-ML (second-ML) molecules with the substrate. Inaddition, this peak shift is consistent with a change in the oxidation state and a reductionof the magnetic moment of the first-ML Mn ion compared to that the free molecule, inagreement with our ab initio calculations.

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µ0H = 0.1 T

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Figure S3: XAS at the Mn edge as a function of molecular coverage. XAS at theMn L3 and L2 edges for left (solid) and right (dashed) photon helicities acquired at a, RTwith 0.1 T and b, 4.8 K with 6.5 T. Helicity averaged spectra corresponding to the whiteline at c, RT with 0.1 T and d, 4.8 K with 6.5 T. For c, and d, vertical dashed lines arepositioned at 647.1 and 648.5 eV. All XAS are normalized to the integral of the white lineintensity in order to obtain spectra independent of the quantity of probed molecules.





3 Density functional theory

3.1 Methods

Our density-functional calculations were performed using the VASP package42 and thegeneralized gradient approximation for exchange-correlation potential as parametrized byPerdew, Burke, and Ernzerhof.43 We used the projector augmented wave (PAW) pseudopo-tentials as provided by VASP.44 Fcc Co(100) surface was modeled by using a supercell of3 atomic monolayers of 8x8 atoms separated by a vacuum region of 3 nm. Since exper-iments used cobalt epitaxially grown on Cu, we used a fcc lattice parameter of 0.36 nmfor cobalt. A kinetic energy cutoff of 450 eV was used for the plane-wave basis set andthe first Brillouin zone was sampled at the Gamma point. The optimized structure of thefirst MnPc layer adsorbed at 2.1 Å away from Co is obtained including the van der Waalsinteractions within the so called GGA-D2 approach developed by Grimme45 and later im-plemented in the VASP package.33 Spin-orbit coupling was included perturbatively in theaugmentation region at each atomic site. Molecular adsorption at 8◦ away from the [011]direction minimized the total energy of the Co/MnPc (1ML) system.

We then explored adding a second and third MnPc layer by taking into account severalgeometries of the relative Pc layers depending on three scenarii to position the top MnPcmolecule’s Mn site onto the bottom MnPc molecule: hollow, on top of N, and on top ofMn with the molecule rotated by 45◦(see Fig. S5a). Here, to draw a trend of magneticcoupling away from the interface, we investigated these multiples geometrical and magneticconfigurations without including vdW forces that are very CPU-intensive for such a largesystem. The adsorption angle of the 1st MnPc molecule remained at 8◦.

Then, to more realistically describe the system, we examined the impact of vdW forcesfor one intermolecular configuration while adopting the 60◦ adsorption angle found fromSTM experiments (see Fig. S2). Including vdW forces, we obtain the correct intermolec-ular distance of around 3.4 Å. A comparison with identical calculations performed for an8◦ adsorption angle reveals that neither the adsorption distance between first ML MnPcand Co, nor the Mn magnetic moment, change upon altering the absorption angle. Thisallows us to draw upon the entire dataset (with/without vdW, at 8◦ or 60◦) to describethe magnetic properties of MnPc molecules adsorbed onto and away from Co.

3.2 Magnetic properties of MnPc on Co

The adsorption and the hybridization-induced ferromagnetic (FM) coupling and high spinpolarization of a single MnPc molecule lying onto a fcc Co(100) surface are discussed indetail in Djeghloul et al. 2013.46 The molecule is calculated to adsorb at 8◦ relative tothe [011] direction of Co(100). The Mn ion lies in a bridge position and the axes of themolecule are slightly rotated compared to the x and y axes defined by the underlyingCo (see Fig. S4a). As a result of the hybridization of the first-ML molecule with the Cosubstrate, the molecule is strongly distorted (see Fig. S4b) compared to the case of a third-ML molecule that is distortion-free (see Fig. S4c). In Fig. S4d, we display for a first-MLMnPc molecule the height of the nitrogen ions relative to the Mn ion. The nitrogen ionsclosest to the Mn ion exhibit a strongly anisotropic height distribution: the nitrogen ionsare on average higher along the x direction than the y direction. For the carbon atomsit is the opposite, the carbon atoms belonging to the lobes along the x direction are onaverage lower then those belonging to the lobes along the y direction.

As a result of the strong hybridization and the electronegativity of the molecule, theMnPc molecule gains about 3.5 electrons from the Co substrate. A Bader analysis reveals

that the manganese ion has a charge of +1.03 |e|, thus lowering its oxidation state. Dueto this charge transfer and the electronic screening of the Mn spin moment, the resultingmagnetic spin moment is reduced from 3.1 to 2.54 µB.

In order to quantify the implications of the topological anisotropy, which arises fromthe Mn adsorption site and the anisotropic N cage around the Mn, on the magnetic prop-erties, we investigated the in-plane magnetic anisotropy. The magnetic anisotropy energywas calculated as the difference in total energies obtained for two different magnetizationdirections (x and y) and is found to be 0.66 meV/supercell. This leads to a magnetizationeasy axis along the x direction. Indeed, the magnetic anisotropy energy per Mn site is 0.39meV, which is the largest contribution to the in plane anisotropy of the supercell.

y

x

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x

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a b c d-0.1972

0.0392

0.1180

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Figure S4: Magnetic anisotropy of the first-ML molecules. a, Single MnPc moleculelying on the Co(100) substrate after atomic relaxations, including van der Waals interac-tions. b, Side-view of the highly distorted first-ML molecule. Increasing z values indicatean increasing distance away from the Co surface. c, Third-ML molecule as computed insection 3.3 with almost no distortion. d, Zoom onto the Mn ion and the nitrogen cage ofa first-ML MnPc molecule. The numbers indicate the relative height with respect to theMn center, expressed in Å.

3.3 The different adsorption geometries and inter-molecule magneticcoupling

In order to support the experimental observations of a second-ML molecule with a magneticreferential that is antiferromagnetically (AF) aligned relative to that of a first-ML molecule,we performed calculations on a system composed of two molecules, one on top of theother, and a Co substrate. As the adsorption site of the MnPc molecules could not beexperimentally resolved, we first considered 3 different adsorption geometries, and did notinclude vdW forces so as to draw a general trend. a) The second-ML molecule is rotated by45◦ relative to the first ML (see Fig. S5a). This configuration corresponds to that observedby Chen et al.47 on first- and second-ML CoPc adsorbed onto a Pb substrate. b) The Mnion of the second-ML molecule is positioned on top of a N site of the first-ML molecule(see Fig. S5b). This configuration is similar to the adsorption geometry between second-and third-ML CoPc adsorbed onto Pb as observed by Chen et al.47 c) The second-ML Mnion lies in a hollow site of the first-ML molecule as represented in Fig. S5c.

The total energy of the system is computed by imposing either a FM or an AF align-ment of the Mn moment of the second ML relative to the first-ML Mn’s spin moment. Asreported in Table 1, the AF coupling is favored for the three configurations we consid-ered. The energetically most favorable geometry corresponds to configuration a, followed





by b and c. However, the difference in total energy between the different configurations isrelatively small. This makes it difficult to unambiguously ascertain the actual experimen-tal configuration. Nevertheless, regardless of the geometry, we find almost identical spinmagnetic moment on the Mn ion, while the strength of the magnetic coupling seems tobe affected. As a note, the large 3.87 Å intermolecular distance that is found for all threeconfigurations reflects the absence of vdW forces in our calculations.

To confirm this trend, and to investigate the impact of molecular adsorption angle,we then included vdW forces on the (a) configuration (see Fig. S5a), but we chose anadsorption angle of ≈60◦ relative to the [011] direction of fcc Co(100). We note thatneither the adsorption distance between first ML MnPc and Co, nor the Mn magneticmoment, change upon this minor alteration to the absorption angle. This allows us tointegrate this calculation into our overall results.

In turn, including vdW forces for the Co(100)/MnPc(2ML) system decreases the in-termolecular distance from 3.87Å to 3.44Å, in line with the literature for bulk MnPc.Furthermore, we find a preferred AF state between the Mn of the two monolayers. Inparticular, we find magnetic moments of 2.47µB and -3.01µB on the 1st and 2nd ML Mnsites. These values are almost identical to the 2.51µB and -3.04µB found without includingvdW forces. This shows that the magnetic trends inferred from our calculations withoutvdW forces ought to be correct.

Performing DFT calculations on a system comprising a Co substrate and three or moreMnPc molecules proved challenging not only because of the sheer number of atoms (over250 sites), but also because of the number of possible adsorption scenarii, some of whichrequire enlarging the unit supercell. We suppose that, much as was found for the similarCoPc molecule,48 most of these scenarii lead to an AF correlation between the Mn sites ofthe molecular planes. To simplify the task here, we considered a Co/MnPc(3 ML) systemin which, starting from Config. a, a third-ML MnPc molecule is adsorbed in a hollow siteas presented in Fig. 3 of the manuscript. We find a preferred AF order of the third-MLMnPc relative to the second-ML MnPc, though with a weak exchange energy of 0.132meV that does not quantitatively reflect the at least 8 meV deduced experimentally fromthe measured blocking temperature of ≈100 K. This discrepancy could arise from havingpicked an incorrect adsorption geometry among the many possible scenarii for three MnPcmolecules.

a b c

Figure S5: The different adsorption geometries calculated for the second-MLMnPc. a, The second-ML molecule is sitting on top of the first ML, rotated by 45◦. b,The second-ML is laterally shifted such that the second-ML Mn ion is positioned on topof an underlying N ion. c, The second-ML molecule is laterally shifted compared to thefirst-ML molecule, such that the Mn ion sits in a hollow position.

Config. a Config. b Config. c

EFM (eV) -2081.873 -2081.879 -2081.858

EAF (eV) -2081.906 -2081.884 -2081.865

EFM − EAF (meV) 33 5 7

EFM − EAF (K) 384 59 79

mMn1s (µB) 2.51 2.54 2.53

mMn2s (µB) -3.04 -3.045 -3.05

dMn1−Mn2 (Å) 3.87 4.36 4.22

∆z (Å) 3.87 3.87 3.87

Table 1: For each of the three different adsorption geometries of Fig. S5, ab-initio calcu-lations yield : the total energy of FM and AF configurations EFM(AF), the spin magneticmoment mMni

s , i = 1, 2 and distance dMn1−Mn2 between the Mn sites of first- and second-ML MnPc, and the distance ∆z perpendicular to the surface between the two Mn atoms.





4 Exchange bias experiments

As described in the main manuscript, we performed magneto-optic Kerr effect measure-ments to unravel the macroscopic magnetic properties of the Cu(100)//Co(20ML)/MnPc-(25ML)/Au(20ML) sample. In Fig. S6 we show a hysteresis loop acquired at 25 K aftercooling in an in-plane magnetic field of +200 mT along [001]. The loop is shifted towardsnegative magnetic fields. This shift switches sign upon reversing the direction of appliedfield upon cooldown (see Fig. S6), which is a signature of EB.

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-0.5

-1.0

Ellipticity

(arb.units)

3002001000-100-200-300

µ0H (mT)

FC +200mT FC -200mT

Figure S6: Magneto-optic Kerr effect measurements onCu(100)//Co(20ML)/MnPc(25ML)/Au(20ML). Magnetic hysteresis loop mea-sured at 25 K after cooling the sample from RT in a in-plane field of +200 mT (blue) and-200 mT (red).

1.0

0.5

0.0

-0.5

-1.0

Ellipticity

(arb.units)

-300 -200 -100 0 100 200 300

µ0H (mT)

T=14 K

Figure S7: Magneto-optic Kerr effect measurements onCu(100)//Co(20ML)/MnPc(25ML)/Au(20ML) field cooled in a out-of-plane magnetic field. Magnetic hysteresis loop measured at 14 K after cooling thesample from RT in a out of plane field of +1.2 T. The loop is horizontally centered andthus reveal no EB.

In order to observe EB, the AF layer needs to bring an additional unidirectionalanisotropy. The unidirectional character of the anisotropy comes from the homogeneousmagnetic ordering of the AF at the FM/AF interface, which is generally realized using anappropriate magnetic field along the AF easy axis during the cooling process (in the sam-ple’s plane for the investigated system, see Fig. S6). Yet, if the magnetic field is applied

in a normal direction to the easy axis during the cooling process, the magnetic ordering ofthe AF at the FM/AF interface is no longer homogeneous and the sample can no longershow EB. We verified this last point by cooling the sample in an out-of-plane magneticfield of 1.2 T and measured the subsequent in-plane magnetic hysteresis loop at 14 K (seeFig. S7).

1.0

0.5

0.0

-0.5

-1.0

Elli

ptic

ity(a

rb.u

nits

)

-200 -100 0 100 200

µ0H (mT)

300 K54 K14 K

-1.0

-0.5

0.0

0.5

1.0

Elli

ptic

ity(a

rb.u

nits

)

-200 -100 0 100 200

µ0H (mT)

300 K14 K

-60

-40

-20

0

Bia

s(m

T)

12010080604020

Temperature (K)

0ML MnPc10ML MnPc25ML MnPc

a b

c

10ML MnPc 0ML MnPc

Figure S8: Temperature and MnPc thickness dependence ofthe exchange bias. Hysteresis loops acquired at different tem-peratures on a, Cu(100)//Co(20ML)/MnPc(10ML)/Au(20ML) and b,Cu(100)//Co(20ML)/MnPc(0ML)/Au(20ML). c, Temperature dependence of theexchange bias in Cu(100)//Co(20ML)/MnPc(x ML)/Au(20ML) where x = 0, 10 and 25ML. The cooling was proceeded in the presence of a in-plane magnetic field of +200 mTand the sample was warmed up to 150 K between each measurements for reset. The loopsin a were smoothed using a 12-point median filter. The open symbols in c correspond tomeasurement acquired with a 10 times higher field sampling, i.e. an acquisition speed 10times slower.

We also performed MOKE measurements on Cu(100)//Co(20ML)/MnPc(10ML)/Au-(20ML) (see Fig. S8a). When decreasing the temperature, the width of the hysteresis loopdrastically increases and the loop is more and more shifted towards negative fields. Thisbehavior is also observed for the hysteresis loops acquired on Cu(100)//Co(20ML)/MnPc-(25ML)/Au(20ML) presented in Fig. 4a of the main manuscript. If the MnPc layer isentirely omitted, the hysteresis loop remains centered and only a low increase in the widthof the loop is observed at low temperature (see Fig. S8b). This clearly demonstrates thekey role of MnPc molecules for the observed exchange bias. Additionally, the strengthof the exchange bias depends on the MnPc thickness (see Fig. S8c) in analogy to theAF-thickness dependence observed in inorganic systems.49 Indeed, at 14 K the bias isabout 65 mT for 25 ML MnPc, only about 20 mT for 10 ML MnPc and 0 mT for 0 MLMnPC. This also indicates that the minimal MnPc thickness required to pin the FM Colayer is between 0 and 10 ML. For the different samples we investigated, the exchange





bias gradually decreases with increasing temperature and vanishes about 100 K, whichdefines the blocking temperature (see Fig. S8c). This shows the reproducible characterof the experiment. Note that for the sample with 10 ML MnPc, we observe dynamiceffects (i.e. the hysteresis loop depends on the field sweeping speed) close to the blockingtemperature that are out of the scope of this paper. Also, the loop asymmetry could reflectthe manifestation of magnetic disorder upon reversing the magnetization. Indeed, while thefirst magnetization reversal is square-like, the return is significantly canted. Subsequentmeasurements reveal a rapid decrease in the amplitude of exchange bias (see e.g. Fig.S9). This substantial training effect presumably underscores the magnetic fragility of theCo(100)/MnPc interface. Future work should focus on FM/molecule systems that can leadto more robust exchange bias.

-15

-10

-5

0

Bias(mT)

321Loop number

Figure S9: Evolution of the exchange bias with subsequent loops. Bias as a functionof the magnetic hysteresis loop for Cu(100)//Co(20ML)/MnPc(10ML)/Au(20ML), mea-sured at 14 K after cooling from RT in a in-plane magnetic field of 0.2 T. The amplitudeof the bias rapidly decreases indicating a strong training effect.

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