Only three elements are ferromagnetic at room temperature: the transition metals iron, cobalt and nickel. The Stoner criterion explains why iron is ferromagnetic but manganese, for example, is not, even though both elements have an unfilled 3d shell and are adjacent in the periodic table: according to this criterion, the product of the density of states and the exchange integral must be greater than unity for spontaneous spin ordering to emerge1,2. Here we demonstrate that it is possible to alter the electronic states of non-ferromagnetic materials, such as diamagnetic copper and paramagnetic manganese, to overcome the Stoner criterion and make them ferromagnetic at room temperature. This effect is achieved via interfaces between metallic thin films and C60 molecular layers. The emergent ferromagnetic state exists over several layers of the metal before being quenched at large sample thicknesses by the material’s bulk properties. Although the induced magnetization is easily measurable by magnetometry, low-energy muon spin spectroscopy3 provides insight into its distribution by studying the depolarization process of low-energy muons implanted in the sample. This technique indicates localized spin-ordered states at, and close to, the metal–molecule interface. Density functional theory simulations suggest a mechanism based on magnetic hardening of the metal atoms, owing to electron transfer4,5. This mechanism might allow for the exploitation of molecular coupling to design magnetic metamaterials using abundant, non-toxic components such as organic semiconductors. Charge transfer at molecular interfaces may thus be used to control spin polarization or magnetization, with consequences for the design of devices for electronic, power or computing applications (see, for example, refs 6 and 7).
Subscribe to Journal
Get full journal access for 1 year
only $3.90 per issue
All prices are NET prices.
VAT will be added later in the checkout.
Rent or Buy article
Get time limited or full article access on ReadCube.
All prices are NET prices.
Stoner, E. C. Collective electron ferromagnetism. Proc. R. Soc. London Ser. A 165, 372–414 (1938)
Stoner, E. C. Collective electron ferromagnetism. II. Energy and specific heat. Proc. R. Soc. London Ser. A 169, 339–371 (1939)
Drew, A. J. et al. Direct measurement of the electronic spin diffusion length in a fully functional organic spin valve by low-energy muon spin rotation. Nature Mater. 8, 109–114 (2009)
Vandewal, K. et al. Efficient charge generation by relaxed charge-transfer states at organic interfaces. Nature Mater. 13, 63–68 (2014)
Callsen, M., Caciuc, V., Kiselev, N., Atodiresei, N. & Bluegel, S. Magnetic hardening induced by nonmagnetic organic molecules. Phys. Rev. Lett. 111, 106805 (2013)
Moodera, J. S., Koopmans, B. & Oppeneer, P. M. On the path toward organic spintronics. MRS Bull. 39, 578–581 (2014)
Raman, K. V. Interface-assisted molecular spintronics. Appl. Phys. Rev. 1, 031101 (2014)
Beeler, M. C. et al. The spin Hall effect in a quantum gas. Nature 498, 201–204 (2013)
Eerenstein, W., Mathur, N. D. & Scott, J. F. Multiferroic and magnetoelectric materials. Nature 442, 759–765 (2006)
Powell, A. K. Molecular magnetism: a bridge to higher ground. Nature Chem. 2, 351–352 (2010)
Geng, Y. et al. Direct visualization of magnetoelectric domains. Nature Mater. 13, 163–167 (2014)
Warner, M. et al. Potential for spin-based information processing in a thin-film molecular semiconductor. Nature 503, 504–508 (2013)
Maccherozzi, F. et al. Evidence for a magnetic proximity effect up to room temperature at Fe/(Ga,Mn) As interfaces. Phys. Rev. Lett. 101, 267201 (2008)
Vobornik, I. et al. Magnetic proximity effect as a pathway to spintronic applications of topological insulators. Nano Lett. 11, 4079–4082 (2011)
Barraud, C. et al. Unravelling the role of the interface for spin injection into organic semiconductors. Nature Phys. 6, 615–620 (2010)
Sanvito, S. Molecular spintronics: the rise of spinterface science. Nature Phys. 6, 562–564 (2010)
Raman, K. V. et al. Interface-engineered templates for molecular spin memory devices. Nature 493, 509–513 (2013)
Brede, J. et al. Long-range magnetic coupling between nanoscale organic-metal hybrids mediated by a nanoskyrmion lattice. Nature Nanotechnol. 9, 1018–1023 (2014)
Pai, W. W. et al. Optimal electron doping of a C60 monolayer on Cu(111) via interface reconstruction. Phys. Rev. Lett. 104, 036103 (2010)
Xu, G. et al. Detailed low-energy electron diffraction analysis of the (4 × 4) surface structure of C60 on Cu(111): seven-atom-vacancy reconstruction. Phys. Rev. B 86, 075419 (2012)
Tamai, A. et al. Electronic structure at the C60/metal interface: an angle-resolved photoemission and first-principles study. Phys. Rev. B 77, 075134 (2008)
Cho, S. W. et al. Origin of charge transfer complex resulting in ohmic contact at the C60/Cu interface. Synth. Met. 157, 160–164 (2007)
Zhang, X. et al. Observation of a large spin-dependent transport length in organic spin valves at room temperature. Nature Commun. 4, 1392 (2013)
Moorsom, T. et al. Spin-polarized electron transfer in ferromagnet/C60 interfaces. Phys. Rev. B 90, 125311 (2014)
Tseng, T.-C. et al. Charge-transfer-induced structural rearrangements at both sides of organic/metal interfaces. Nature Chem. 2, 374–379 (2010)
Janak, J. F. Uniform susceptibilities of metallic elements. Phys. Rev. B 16, 255–262 (1977)
Morenzoni, E. et al. Implantation studies of keV positive muons in thin metallic layers. Nucl. Instrum. Methods B192, 254–266 (2002)
Ansaldo, E. J., Niedermayer, C. & Stronach, C. E. Muonium in fullerite. Nature 353, 121 (1991)
Duty, T. L. et al. Zero-field μSR in crystalline C60 . Hyperfine Interact. 86, 789–795 (1994)
Coey, J. M. D. d0 ferromagnetism. Solid State Sci. 7, 660–667 (2005)
Bakule, P. & Morenzoni, E. Generation and applications of slow polarized muons. Contemp. Phys. 45, 203–225 (2004)
Prokscha, T. et al. The new μE4 beam at PSI: a hybrid-type large acceptance channel for the generation of a high intensity surface-muon beam. Nucl. Instrum. Methods A595, 317–331 (2008)
Morenzoni, E. et al. Generation of very slow polarized positive muons. Phys. Rev. Lett. 72, 2793–2796 (1994)
Schwarz, K. & Mohn, P. Itinerant metamagnetism in YCO2 . J. Phys. F Met. Phys. 14, L129–L134 (1984)
Kresse, G. & Furthmuller, J. Efficient iterative schemes for ab initio total-energy calculations using a plane-wave basis set. Phys. Rev. B 54, 11169–11186 (1996)
Perdew, J. P., Burke, K. & Ernzerhof, M. Generalized gradient approximation made simple. Phys. Rev. Lett. 77, 3865–3868 (1996)
Methfessel, M. & Paxton, A. T. High-precision sampling for Brillouin-zone integration in metals. Phys. Rev. B 40, 3616–3621 (1989)
This work was supported by the Engineering and Physical Sciences Research Council through grants EP/K00512X/1, EP/K036408/1, EP/J01060X/1 and EP/I004483/1. Use of the N8 POLARIS (EPSRC EP/K000225/1), ARCHER (via the UKCP Consortium, EP/K013610/1), and the High Performance Computing (HPC) Wales facilities is acknowledged. Use of the National Synchrotron Light Source, Brookhaven National Laboratory, was supported by the US Department of Energy, Office of Science, Office of Basic Energy Sciences, under contract number DE-AC02-98CH10886.
The authors declare no competing financial interests.
The data presented here are available at http://dx.doi.org/10.5518/6.
About this article
Cite this article
Ma’Mari, F., Moorsom, T., Teobaldi, G. et al. Beating the Stoner criterion using molecular interfaces. Nature 524, 69–73 (2015) doi:10.1038/nature14621
Physical Review Materials (2019)
Nano Materials Science (2019)
Physical Review B (2019)
Applied Physics Express (2019)
Controlling Ferromagnetic Ground States and Solitons in Thin Films and Nanowires Built from Iron Phthalocyanine Chains
Advanced Functional Materials (2019)