Article
pubs.acs.org/JPCC

Magnetic Interactions of Vanadyl Phthalocyanine with
Ferromagnetic Iron, Cobalt, and Nickel Surfaces
Keitaro Eguchi,† Yasumasa Takagi,†,‡ Takeshi Nakagawa,†,‡ and Toshihiko Yokoyama*,†,‡†

Department of Structural Molecular Science, The Graduate University for Advanced Studies (SOKENDAI), Myodaiji-cho, Okazaki444-8585, Japan‡
Department of Materials Molecular Science, Institute for Molecular Science, Myodaiji-cho, Okazaki 444-8585, JapanS Supporting Information*

ABSTRACT: We have investigated the molecular orientation and magnetic properties of vanadyl
phthalocyanine (VOPc) deposited on ferromagnetic Fe, Co, and Ni ﬁlms, which were epitaxiallygrown on Cu(001) using X-ray absorption spectroscopy and X-ray magnetic circular dichroism. The
results reveal that the VOPc framework lies ﬂat on the surfaces with oxygen-up conﬁgurations. The
spin of the central V atoms in VOPc is antiferromagnetically coupled with those of Fe or Co atoms in the ferromagnetic surface.
In contrast, the magnetic coupling between V and Ni is not eﬀective, exhibiting simple paramagnetism of VOPc.

1. INTRODUCTION
Magnetic interactions of the central metal ions in metal
phthalocyanines (MPcs) and metal porphyrins (MPs) withferromagnetic surfaces have attracted signiﬁcant attention fromthe viewpoint of scientiﬁc interests at the interfaces and also fortechnological applications, such as chemical switches1,2 andgiant magnetoresistance.3 The ferromagnetic coupling between
the central Mn ion in Mn porphyrin and the ferromagnetic Co
ﬁlm at the interface has been shown element speciﬁcally using
X-ray magnetic circular dichroism (XMCD) by Scheybal andco-workers.4 The study revealed that the coupling is eﬀective at
the interface between the adsorbed molecule and ferromagnetic
ﬁlm. Similar ferromagnetic couplings have been reported inseveral systems, including Fe porphyrin on Co and Ni,5,6 MnPc
on Co(001),7 Co porphyrin on Ni,1 and Cu porphyrin on
Fe3O4(100).8 On the other hand, Ni porphyrin deposited
directly on Co does not show any magnetic coupling due to theabsence of the net spin in the central Ni ion.9 Based ontheoretical calculations, Wende et al. ascribed the mechanism offerromagnetic coupling to the superexchange interaction
between the central ion and ferromagnetic surfaces via nitrogenin the ligand.5 Furthermore, Chylarecka et al. experimentally
substantiated the mechanism of the superexchange coupling
using rough and smooth Co surfaces in combination with thetheoretical calculation.10
Antiferromagnetic coupling of the central metal ions with theferromagnetic surfaces has been realized in Fe porphyrin11,12
and Mn porphyrin13 deposited on oxygen-covered ferromagnetic ﬁlms. In these systems, the central metal ions are coupled
antiferromagnetically to the ferromagnetic surfaces, which issimilar to the superexchange interaction via oxygen atoms in
the antiferromagnetic metal oxides. Another kind of antiferromagnetic coupling was observed in TbPc2 adsorbed on the
ferromagnetic Ni substrate.14 In this system, the Tb spin iscoupled antiferromagnetically with that of the Ni surface atom
via the phthalocyanine ligand. Furthermore, exchange bias was© 2014 American Chemical Society

demonstrated in TbPc2 deposited on the antiferromagnetic Mnﬁlm.15The magnetic interaction of the 3d-transition metal series in
the MPcs and MPs adsorbed on bare (oxygen-covered)ferromagnetic surfaces has always been ferromagnetic (antiferromagnetic). However, the experimental observations ofthese magnetic interactions are limited in the cases of MPcs andMPs (M = Mn, Fe, Co, Cu). For early transition elements, suchas V and Cr, the magnetic interactions with the ferromagnetic
surfaces have been veiled. Therefore, in the present study, toreveal the underlying magnetic interactions, we have considered
vanadyl phthalocyanine (VOPc) that has a spin (S = 1/2) inthe central V ion.16,17
In this study, we have investigated the molecular orientationand magnetic properties of VOPc deposited on ferromagnetic
Fe, Co, and Ni surfaces using element speciﬁc X-ray absorption
spectroscopy (XAS) and XMCD measurements. VOPc is foundto lie ﬂat on the ferromagnetic surfaces with an oxygen-up
conﬁguration. The results indicate eﬀective antiferromagnetic
coupling of the central V ions with the ferromagnetic Fe andCo surfaces. On the contrary, VOPc deposited on the Ni
surface exhibits almost no eﬀective magnetic interaction at themeasurement temperature of 5 K.

2. EXPERIMENTAL SECTION
The sample preparation was performed under ultrahigh vacuum
conditions (P ≈ 4 × 10−8 Pa). A Cu(001) substrate was cleanedby repeating a cycle of Ar ion sputtering and annealing at 800
K. Low-energy electron diﬀraction (LEED) of the Cu substrateexhibited a sharp (1 × 1) pattern which is shown in the
Supporting Information. The amount of carbon contamination,
estimated using Auger electron spectroscopy, was found to beless than 2% (see the Supporting Information). Subsequently, aReceived: April 20, 2014
Revised: July 13, 2014
Published: July 14, 2014
17633

dx.doi.org/10.1021/jp503851k | J. Phys. Chem. C 2014, 118, 17633−17637

The Journal of Physical Chemistry C

Articleferromagnetic Fe ﬁlm was prepared on the Cu(001) by electron
bombardment evaporation. During this process, the substrate
was maintained at a relatively low temperature (T ≈ 110 K) to
avoid the formation of an Fe−Cu alloy. The Fe ﬁlm was
epitaxially grown on the substrate for up to 3 ML (monolayer)
thickness, as conﬁrmed from the reﬂection high-energy electron
diﬀraction oscillations (see Supporting Information). Co andNi ﬁlms were also prepared using the above-mentioned
procedure, but the substrate temperature was kept at room
temperature during the evaporation. The thickness of the Co
and Ni ﬁlms thus obtained was estimated to be 3 and 4 ML,
respectively.
Subsequently, sublimation-puriﬁed VOPc was deposited on
the ferromagnetic ﬁlms at room temperature using a homemade Knudsen cell evaporator ﬁtted with an alumel−chromel(K-type) thermocouple. The deposition rate of VOPc wascontrolled at ∼0.1 ML/min by adjusting the cell temperature to530 K. LEED images of the samples were taken and LEED
spots originating from VOPc were observed for VOPc on Co
and Ni, while those of VOPc on Fe were unclear (see theSupporting Information). Details of the sample preparation
procedure have been reported in the literature16 and is also
given in the Supporting Information.
The in situ XAS and XMCD measurements were performed
using an XMCD system (P < 1 × 10−8 Pa, μ0H = 7 T, T = 3.8
K) at the end station of the bending magnet Beamline 4B of
UVSOR−III of Institute for Molecular Science (IMS), Okazaki,
Japan. Details of the XMCD measurement system have beenreported elsewhere.18,19 Angle-dependent N K-edge XAS
measurements were performed using linearly polarized X-rays,
incident at an angle θ of 0°, 30°, and 55° with respect to thesurface normal. The samples were rotated around the [110]axis, ensuring that the X-ray electric ﬁeld vector was always inthe (110) plane. Furthermore, circularly polarized XAS andXMCD spectra were obtained by the total electron yielddetection mode in a magnetic ﬁeld of 0 or ±5 T, at thetemperature of 5 K and X-ray incidence angles of 0° and 55°.
The circular polarization degree of the X-rays was estimated tobe ∼0.6 from the beamline parameters. The magnetic ﬁeld wasapplied to the sample in parallel or antiparallel geometries withrespect to the X-ray beam. The X-ray energy was calibratedusing L-edge XAS of metallic V, Fe, Co, and Ni ﬁlms. The
nominal energy resolution (ΔE) was estimated to be 0.8 eV at
the V L edge and 1.0 eV at the Fe, Co, and Ni L edges. The
reproducibility of XAS and XMCD spectra was conﬁrmed bytheir repeated measurements.

Figure 1. Angle-dependent linearly polarized N K-edge XAS of 0.9 ML
VOPc on (a) 3 ML Fe, (b) 3 ML Co, and (c) 4 ML Ni ﬁlms grown
epitaxially on Cu(001). The measurement temperature was 5 K. Theenergy resolution (ΔE) was 0.3 eV at the photon energy of 400 eV.

in MnPc physisorbed on Cu(001) and is further shifted to alower energy side in MnPc chemisorbed on Co(001) due tocharge transfer from Co to ligand N.7 On the other hand, in thecases of FePc22 and ZnPc23 on TiO2(110), such satellite peaks
appear at a higher photon energy side of the main π* peaks due
to charge transfer from the molecules to the substrates. In thepresent study, peak S can thus be attributed at least partially tothe transition to the σ* orbital of V−N, which is shifted towarda lower energy side than peak A due to chemical interaction,
probably a charge transfer eﬀect, between the N atoms in VOPc
and Fe surface. Polarization dependence of peak S is however
found to be quite weak in Figure 1, indicating somecomplicated nature of the origin of peak S. We can supposethat the peak originates from the V−N σ* resonance and also
some π* transition.
The XAS results indicate that VOPc adsorbs with an oxygenup conﬁguration. This is conﬁrmed by the V L- and O K-edge
XAS of VOPc on Fe because the spectral shape and the peak
position in the XAS of VOPc on Fe (Figure 2a) is similar tothat of VOPc on Ag, where the oxygen atom is known to be
directed upward.16 In the cases of the Co and Ni surfaces, thespectral shape and the peak position in the XAS of VOPc (seeFigures 3a and 4a) are almost similar to those of VOPc on Fe,

3. RESULTS AND DISCUSSION
Figure 1 shows the angle-dependent N K-edge XAS of VOPc.
All the samples exhibit peaks A, B, and C attributed mainly tothe transition from N 1s to π* molecular orbitals.20,21 On theother hand, peak S is detected only in the XAS of VOPc
deposited on the Fe surface. The intensity of the π* peaks
increases gradually with the tilting of the X-ray electric ﬁeld
vector from the surfaces. This indicates that the phthalocyanine
framework in the samples lies almost ﬂat with respect to thesurfaces. Satellite peaks such as peak S in VOPc on Fe havebeen observed in the system of adsorbed molecules oninteractive surfaces7,22,23 and peak S resembles the spectrumof MnPc on Co(001).7 In the MnPc/Co system, the satellite
peak has been ascribed to the transition from the N 1s orbitalto the σ* orbital of Mn−N by the theoretical calculation.7 This
peak appears at almost the same energy of the lowest π* peakFigure 2. (a) V L-, O K-, and (b) Fe L-edge XAS and the XMCD
spectra of 0.9 ML VOPc on 3 ML Fe/Cu(001) at a temperature of 5K, magnetic ﬁeld of ±5 T, and X-ray incidence angles of 0° (normal
incidence) and 55° (grazing incidence). The green dashed line
represents the integral of μ+−μ− from 507 to 527 eV.
17634

dx.doi.org/10.1021/jp503851k | J. Phys. Chem. C 2014, 118, 17633−17637

The Journal of Physical Chemistry C

Articlewould not be aﬀected even if a small amount of bilayer stacking
VOPc is formed.
Furthermore, we performed element speciﬁc XMCD
measurements to gain deeper insights on the magnetic
properties of VOPc deposited on the ferromagnetic surfaces.
The XMCD spectra of VOPc on Fe are shown in Figure 2.
Although the strong interaction of ligand N with the Fe ﬁlm
and satellite peak S was observed in N K-edge XAS, nosigniﬁcant change in Fe L-edge XAS/XMCD was detected
between clean Fe and VOPc/Fe (see the Supporting
Information). The V L-edge XMCD signals are clearly observedin both the 0° and 55° conﬁgurations, implying that the V spinis preserved at the interface without losing the spin against to
the case of CoPc on the Fe ﬁlm in which the spin of CoPc
vanishes at the CoPc/Fe interface.24 The Fe ﬁlm is magnetizedalong the magnetic ﬁeld, and the magnetization is saturated at 5
T in both the 0° and 55° conﬁgurations (magnetization curvesof the ferromagnetic ﬁlms are shown in the Supporting
Information). In contrast to the Fe ﬁlm, the V ions in thesystem are magnetized in the direction opposite to themagnetic ﬁeld. This implies that the V spins are coupled
antiferromagnetically with those of the Fe ﬁlm. XAS andXMCD spectra of VOPc on Fe measured at remanence are
given in the Supporting Information. The same result wasobserved in the VOPc/Co system, as shown in Figure 3 (XASand XMCD spectra of VOPc on Co measured at remanence arealso shown in the Supporting Information). The L3 peak in the
XMCD spectrum of Co shows a negative sign, while the L3
peak of V exhibits a positive sign. These results are clearly
diﬀerent from the previous cases of MPcs and MPs (M = Mn,
Fe, Co). In the cases of MPs, such as MnTPP (TPP =tetraphenylporphyrin)10 and FeOEP (OEP = octraethylporphyrin), 5 on the ferromagnetic surfaces, the magnetic
interaction between the central metal ions and ferromagnetic
ﬁlms was found to be ferromagnetic. The origin of theferromagnetic interaction in these systems can be explained on
the basis of the superexchange interaction via N atoms bonded
to the central metal ion, given the fact that the distance
between the metal ion and the surface is too large to show
direct exchange interaction and that the theoretical calculations
have predicted the chemical interactions of ligand N with thesurfaces, although the possibility of direct exchange interaction
cannot be completely eliminated for FeOEP.6 On the other
hand, in the MPcs systems, such as MnPc7 and CoPc,25 on Co,
direct exchange couplings are probable because of the shorter
distance between the metal ion and the surface, as compared tothose in the above-mentioned MPs. In the present study,
XMCD measurements indicate antiferromagnetic coupling of Vwith the Fe and Co surfaces. The coupling mechanism can be
explained on the basis of the superexchange interaction via N
atoms.26,27 However, we cannot completely exclude thepossibility of direct exchange interaction between the central
V ions and the ferromagnetic Fe and Co surfaces.
Figure 4 shows the XMCD spectrum of VOPc on Ni surface.
In contrast to that observed in the cases of Fe and Co, thecentral V ion in VOPc on Ni is magnetized at 5 T in the
direction similar to that of the magnetic ﬁeld and the Ni ﬁlm.
To identify the magnetic interaction, the XMCD spectra werealso recorded at the remanent magnetization (μ0H = 0 T). The
corresponding results are indicated as green solid lines in
Figure 4. The Ni L-edge XMCD was not observed at normal Xray incidence, while the signal was observed at the grazing X-ray
incidence, implying in-plane residual magnetization of the Ni

Figure 3. (a) V L-, O K-, and (b) Co L-edge XAS and the XMCD
spectra of 0.9 ML VOPc on 3 ML Co/Cu(001) at a temperature of 5K, magnetic ﬁeld of ±5 T, and X-ray incidence angles of 0° and 55°.
The green dashed line represents the integral of μ+−μ− from 507 to
527 eV.

Figure 4. (a) V L-, O K-, and (b) Ni L-edge XAS and the XMCD
spectra of 0.9 ML VOPc on 4 ML Ni/Cu(001) at a temperature of 5K, magnetic ﬁeld of ±5 T, and X-ray incidence angles of 0° and 55°.
The XMCD spectra taken at remanent magnetization are depicted as
green solid lines.

despite the absence of satellite peak S in N K-edge XAS.
Comparing the N K-edge XAS of VOPc on Co with that of
VOPc on Ni, we notice that the spectrum in the π* region on
Co is broader than that on Ni and the π* peak on Co starts at
the lower energy side than that on Ni, implying stronger
interaction of VOPc with Co than that of VOPc with Ni.
The possibility of bilayer stacking structures of VOPc cannot
be excluded completely from the XAS and other results.
However, it is understood from the LEED images (see theSupporting Information) that deposited VOPc prefers to form
monolayer structures rather than bilayer stacking structures. In
the LEED images of VOPc on Co and Ni, diﬀused LEED spots
originating from VOPc were clearly observed, which indicatesthe formation of relatively densely packed self-assembled states.
In the case of VOPc on Fe, LEED spots were dim incomparison to the other samples due to stronger interaction of
VOPc with Fe. Therefore, we conclude that most VOPc
deposited on Fe, Co, and Ni favors the formation of monolayer,
although small amounts of VOPc possibly form bilayer.
However, the present conclusions concerning electronic andmagnetic interaction of VOPc with the ferromagnetic ﬁlms
17635

dx.doi.org/10.1021/jp503851k | J. Phys. Chem. C 2014, 118, 17633−17637

The Journal of Physical Chemistry C

Articleunusual LS coupling is attributed to the ligand ﬁeld eﬀect
surrounding the V atom has been suggested by using a modelof VAu4 in the theoretical calculations.31

ﬁlm. On the contrary, the V L-edge XMCD signals at 0 T was
not observed clearly in either the 0° or 55° conﬁgurations.
Besides, the shape of the XMCD spectrum at 0 T was obviously
diﬀerent from that at 5 T. These results suggest that the V Ledge XMCD signals at 5 T mainly originate from the simple
Zeeman eﬀect in the molecule itself, and not from theferromagnetic interaction with the Ni ﬁlm. In addition, theweak antiferromagnetic interaction of V with Ni ﬁlm is
expected due to the small V L-edge XMCD signal.
In order to compare the XMCD intensity, we calculated theintegrated values of the V L-edge XMCD intensity for the threesamples analyzed in this study, as summarized in Table 1. Here,

4. SUMMARY
We have investigated the magnetic properties of VOPc
deposited on the ferromagnetic Fe, Co, and Ni surfaces using
element speciﬁc XMCD measurements to demonstrate themagnetic coupling of V (with less than half 3d electron system)
ions with the ferromagnetic atoms in the Fe, Co and Ni
surfaces. In contrast to the previously reported cases offerromagnetic interactions in MPcs and MPs (M = Mn, Fe, Co)
deposited on oxygen-uncovered (bare) ferromagnetic surfaces,
antiferromagnetic coupling was found to be dominant in
VOPc/Fe and VOPc/Co systems. On the other hand, themagnetic interaction of V ions with the Ni surface was rather
ineﬀective, with the Zeeman eﬀect being dominant at thetemperature of 5 K. Thus, the strength of magnetic interactionof VOPc with the ferromagnetic ﬁlms was reduced in the orderof Fe, Co, and Ni ﬁlms. This trend was in the same order withthe strength of the interaction of V with ferromagnetic surfaces
as observed peak S in N K-edge XAS. It is suggested that thesuperexchange interaction via N coexists with the direct
exchange interaction in a short distance between the central
V and the ferromagnetic surfaces.

Table 1. Integrated V L2,3-edge XMCD Intensities in 0.9 ML
VOPc on the Fe, Co, and Ni Filmsa
incidence angle
0°55°

VOPc/Fe

VOPc/Co

VOPc/Ni

1.00
0.35

0.61
0.31

−0.38
−0.23

a

The values are normalized to that of VOPc/Fe at the 0°
conﬁguration. The sign corresponds to the direction of magnetization;a positive (negative) sign indicates that the direction of magnetizationof the central V ion is antiparallel (parallel) with respect to themagnetic ﬁeld and magnetization of the ferromagnetic ﬁlm.

■

the magnetizations of the ferromagnetic ﬁlms were nearlysaturated at 5 T in both the 0° and 55° conﬁgurations, whichwere conﬁrmed from the XMCD intensities of Fe, Co, and Ni
L3-edges. In all the samples, the XMCD intensity of VOPc at 0°
is found to be larger than that at the 55° conﬁguration. The
molecular magnetic anisotropy originates from the spin−orbit
interaction of the 3d-electron in the 3dxy orbital of the V ion.
The integrated values of the V L-edge XMCD intensity show
the reduction trend from Fe to Co and Ni, and the sign of theL3 peak in the XMCD spectrum of VOPc/Ni is reversed whencompared to the other two samples. These imply that theantiferromagnetic interaction of the central V ion with theferromagnetic surfaces weakens in the order of Fe, Co, and Ni
ﬁlms. This tendency is consistent with the cases of FeOEP on
Co and Ni,6 which is related to the strength of the exchangeinteraction of the central V ions with the ferromagnetic
surfaces. In addition, it is found that the order of the strength ofthe magnetic interaction of VOPc with the ﬁlms is in accord
with that of the electronic interaction between ligand N and theferromagnetic surfaces. It is thus expected that the origin of themagnetic interaction is not only direct exchange interaction but
also superexchange interaction via N in the systems of VOPc
on the ferromagnetic ﬁlms.
Finally, we will comment on the direction of the spin andorbital magnetic moments. In the half electron system such as
V, total magnetic momentum J is usually as J = L − S on thebasis of Hund’s third rule and this has been conﬁrmed in manysystems as not only atoms but also molecules, metal complexes,
and bulk materials. In the present study, we cannot
quantitatively evaluate the spin and orbital magnetic momentsfrom the V L-edge XMCD due to the overlap between the V L3and L2 edges and small intensity of the XMCD signal. However,the sign of these magnetic moments can be estimated by using
sum rules related to the XMCD.28,29 The sign of the spin andorbital magnetic moments in the VOPc/Fe and VOPc/Co
systems are same, implying these systems show the coupling of
J = L + S. Similar results obtained by XMCD have been also
reported for VO complexes.30 One interpretation that the

ASSOCIATED CONTENT

S Supporting Information*

Sample preparation, LEED images, and other XAS/XMCD
spectra. This material is available free of charge via the Internet
at http://pubs.acs.org.

■

AUTHOR INFORMATION

Corresponding Author*E-mail: yokoyama@ims.ac.jp. Phone: +81 (564)55 7341. Fax:
+81 (564)55 7337.
Notes

The authors declare no competing ﬁnancial interest.

■

REFERENCES(1) Wackerlin, C.; Chylarecka, D.; Kleibert, A.; Muller, K.; Iacovita,
C.; Nolting, F.; Jung, T. A.; Ballav, N. Controlling Spins in Adsorbed
Molecules by a Chemical Switch. Nat. Commun. 2010, 1, 61.
(2) Ballav, N.; Wäckerlin, C.; Siewert, D.; Oppeneer, P. M.; Jung, T.
A. Emergence of on-Surface Magnetochemistry. J. Phys. Chem. Lett.
2013, 4, 2303−2311.
(3) Schmaus, S.; Bagrets, A.; Nahas, Y.; Yamada, T. K.; Bork, A.;
Bowen, M.; Beaurepaire, E.; Evers, F.; Wulfhekel, W. Giant
Magnetoresistance through a Single Molecule. Nat. Nanotechnol.
2011, 6, 185−189.
(4) Scheybal, A.; Ramsvik, T.; Bertschinger, R.; Putero, M.; Nolting,F.; Jung, T. A. Induced Magnetic Ordering in a Molecular Monolayer.
Chem. Phys. Lett. 2005, 411, 214−220.
(5) Wende, H.; Bernien, M.; Luo, J.; Sorg, C.; Ponpandian, N.;
Kurde, J.; Miguel, J.; Piantek, M.; Xu, X.; Eckhold, P.; et al. SubstrateInduced Magnetic Ordering and Switching of Iron Porphyrin
Molecules. Nat. Mater. 2007, 6, 516−20.
(6) Bernien, M.; Xu, X.; Miguel, J.; Piantek, M.; Eckhold, P.; Luo, J.;
Kurde, J.; Kuch, W.; Baberschke, K. Wende et al., Fe-Porphyrin
Monolayers on Ferromagnetic Substrates: Electronic Structure andMagnetic Coupling Strength. Phys. Rev. B 2007, 76, 214406.
(7) Javaid, S.; Bowen, M.; Boukari, S.; Joly, L.; Beaufrand, J. B.; Chen,
X.; Dappe, Y. J.; Scheurer, F.; Kappler, J. P.; Arabski, J.; Wulfhekel, W.;
Alouani, M.; Beaurepaire, E. Impact on Interface Spin Polarization of

17636

dx.doi.org/10.1021/jp503851k | J. Phys. Chem. C 2014, 118, 17633−17637

The Journal of Physical Chemistry C

ArticleMolecular Bonding to Metallic Surfaces. Phys. Rev. Lett. 2010, 105,
077201.
(8) Klanke, J.; Rentschler, E.; Medjanik, K.; Kutnyakhov, D.;
Schönhense, G.; Krasnikov, S.; Shvets, I. V.; Schuppler, S.; Nagel,
P.; Merz, M.; et al. Beyond the Heisenberg Model: Anisotropic
Exchange Interaction between a Cu-Tetraazaporphyrin Monolayer andFe_{3}O_{4}(100). Phys. Rev. Lett. 2013, 110, 137202.
(9) Wackerlin, C.; Tarafder, K.; Girovsky, J.; Nowakowski, J.; Hahlen,T.; Shchyrba, A.; Siewert, D.; Kleibert, A.; Nolting, F. Oppeneer et al.,Ammonia Coordination Introducing a Magnetic Moment in an onSurface Low-Spin Porphyrin. Angew. Chem., Int. Ed. 2013, 52, 4568−
4571.
(10) Chylarecka, D.; Kim, T. K.; Tarafder, K.; Müller, K.; Gödel, K.;
Czekaj, I.; Wäckerlin, C.; Cinchetti, M.; Ali, M. E.; Piamonteze, C.;et al. Indirect Magnetic Coupling of Manganese Porphyrin to a
Ferromagnetic Cobalt Substrate. J. Phys. Chem. C 2011, 115, 1295−
1301.
(11) Bernien, M.; Miguel, J.; Weis, C.; Ali, M.; Kurde, J.; Krumme,
B.; Panchmatia, P.; Sanyal, B.; Piantek, M.; Srivastava, P.; et al.
Tailoring the Nature of Magnetic Coupling of Fe-Porphyrin Molecules
to Ferromagnetic Substrates. Phys. Rev. Lett. 2009, 102, 047202.
(12) Miguel, J.; Hermanns, C. F.; Bernien, M.; Krüger, A.; Kuch, W.
Reversible Manipulation of the Magnetic Coupling of Single Molecular
Spins in Fe-Porphyrins to a Ferromagnetic Substrate. J. Phys. Chem.
Lett. 2011, 2, 1455−1459.
(13) Chylarecka, D.; Wäckerlin, C.; Kim, T. K.; Müller, K.; Nolting,F.; Kleibert, A.; Ballav, N.; Jung, T. A. Self-Assembly and Superexchange Coupling of Magnetic Molecules on Oxygen-Reconstructed
Ferromagnetic Thin Film. J. Phys. Chem. Lett. 2010, 1, 1408−1413.
(14) Lodi Rizzini, A.; Krull, C.; Balashov, T.; Kavich, J. J.; Mugarza,
A.; Miedema, P. S.; Thakur, P. K.; Sessi, V.; Klyatskaya, S.; Ruben, M.;
et al. Coupling Single Molecule Magnets to Ferromagnetic Substrates.
Phys. Rev. Lett. 2011, 107, 177205.
(15) Lodi Rizzini, A.; Krull, C.; Balashov, T.; Mugarza, A.; Nistor, C.;
Yakhou, F.; Sessi, V.; Klyatskaya, S.; Ruben, M.; Stepanow, S.;
Gambardella, P. Exchange Biasing Single Molecule Magnets: Couplingof Tbpc2 to Antiferromagnetic Layers. Nano Lett. 2012, 12, 5703−
5707.
(16) Eguchi, K.; Takagi, Y.; Nakagawa, T.; Yokoyama, T. Molecular
Orientation and Electronic States of Vanadyl Phthalocyanine on
Si(111) and Ag(111) Surfaces. J. Phys. Chem. C 2013, 117, 22843−
22851.
(17) Assour, J. M.; Goldmacher, J.; Harrison, S. E. Electron Spin
Resonance of Vanadyl Phthalocyanine. J. Chem. Phys. 1965, 43, 159.
(18) Nakagawa, T.; Takagi, Y.; Matsumoto, Y.; Yokoyama, T.
Enhancements of Spin and Orbital Magnetic Moments of Submonolayer Co on Cu(001) Studied by X-Ray Magnetic Circular
Dichroism Using Superconducting Magnet and Liquid He Cryostat.
Jpn. J. Appl. Phys. 2008, 47, 2132−2136.
(19) Yokoyama, T.; Nakagawa, T.; Takagi, Y. Magnetic Circular
Dichroism for Surface and Thin Film Magnetism: Measurement
Techniques and Surface Chemical Applications. Int. Rev. Phys. Chem.
2008, 27, 449−505.
(20) De Francesco, R.; Stener, M.; Fronzoni, G. Theoretical Study ofnear-Edge X-Ray Absorption Fine Structure Spectra of Metal
Phthalocyanines at C and N K-Edges. J. Phys. Chem. A 2012, 116,
2885−2894.
(21) Ahlund, J.; Nilson, K.; Schiessling, J.; Kjeldgaard, L.; Berner, S.;
Martensson, N.; Puglia, C.; Brena, B.; Nyberg, M.; Luo, Y. The
Electronic Structure of Iron Phthalocyanine Probed by Photoelectron
and X-Ray Absorption Spectroscopies and Density Functional Theory
Calculations. J. Chem. Phys. 2006, 125, 34709.
(22) Palmgren, P.; Nilson, K.; Yu, S.; Hennies, F.; Angot, T.; Layet, J.
M.; Le Lay, G.; Göthelid, M. Strong Interactions in Dye-SensitizedInterfaces. J. Phys. Chem. C 2008, 112, 5972−5977.
(23) Yu, S.; Ahmadi, S.; Sun, C.; Adibi, P. T.; Chow, W.; Pietzsch, A.;
Gothelid, M. Inhomogeneous Charge Transfer within Monolayer Zinc
Phthalocyanine Absorbed on Tio2(110). J. Chem. Phys. 2012, 136,
154703.

(24) Brede, J.; Atodiresei, N.; Kuck, S.; Lazić, P.; Caciuc, V.;
Morikawa, Y.; Hoffmann, G.; Blügel, S.; Wiesendanger, R. Spin- andEnergy-Dependent Tunneling through a Single Molecule with
Intramolecular Spatial Resolution. Phys. Rev. Lett. 2010, 105, 047204.
(25) Iacovita, C.; Rastei, M.; Heinrich, B.; Brumme, T.; Kortus, J.;
Limot, L.; Bucher, J. Visualizing the Spin of Individual CobaltPhthalocyanine Molecules. Phys. Rev. Lett. 2008, 101, 116602.
(26) Kanamori, J. Superexchange Interaction and Symmetry
Properties of Electron Orbitals. J. Phys. Chem. Solids 1959, 10, 87−98.
(27) Goodenough, J. B. Magnetism and the Chemical Bond; Wiley:
New York, 1963.
(28) Carra, P.; Thole, B. T.; Altarelli, M.; Wang, X. X-Ray Circular
Dichroism and Local Magnetic Fields. Phys. Rev. Lett. 1993, 70, 694−
697.
(29) Thole, B. T.; Carra, P.; Sette, F.; van der Laan, G. X-Ray
Circular Dichroism as a Probe of Orbital Magnetization. Phys. Rev.
Lett. 1992, 68, 1943−1946.
(30) Gallani, J. L.; Kappler, J. P.; Derory, A.; Ohresser, P.; Turek, P.;
Zangrando, M.; Zacchigna, M.; Parmigiani, F.; Gorecka, E.;
Krowczynski, A. X-Ray Magnetic Circular Dichroism on Vanadium
Molecular Derivatives. Eur. Phys. J. B 2004, 38, 43−48.
(31) Galanakis, I.; Oppeneer, P. M.; Ravindran, P.; Nordström, L.;
James, P.; Alouani, M.; Dreysse, H.; Eriksson, O. Sign Reversal of the
Orbital Moment Via Ligand States. Phys. Rev. B 2001, 63, 172405.

17637

dx.doi.org/10.1021/jp503851k | J. Phys. Chem. C 2014, 118, 17633−17637