Magnetism in thin films of CaB6 and SrB6

Dorneles, L. S.; Venkatesan, M.; Moliner, M.; Lunney, J. G.; Coey, J. M. D.

doi:10.1063/1.1840113

Cited by 76 publications

(46 citation statements)

References 18 publications

(7 reference statements)

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“…Ferromagnetic hysteresis in proton irradiated graphite with the Curie temperature ranging between 500 and 800 K was observed and reported [1][2][3][4]. Permanent giant magnetic moments were detected at the surface layers of thin films of oxides and borides [5][6][7]. Ferromagnetic hysteresis at room temperature was measured in 1.7 nm gold nanoparticles (NPs) surrounded by thiols [8].…”

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confidence: 99%

Origin of Orbital Ferromagnetism and Giant Magnetic Anisotropy at the Nanoscale

2006

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The origin of orbital magnetism recently observed in different nanostructured films and particles is discussed as a consequence of spin-orbit coupling. It is shown that contact potentials induced at the thin film surface by broken symmetries, as domain boundaries in self-assembled monolayers, lead to orbital states that in some cases are of large radius. The component of the angular momentum normal to the surface can reach very high values that decrease the total energy by decreasing spin-orbit interaction energy. Intraorbital ferromagnetic spin correlations induce orbital momenta alignment. The estimated values of the magnetic moments per atom are in good agreement with the experimental observations in thiol capped gold films and nanoparticles.

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confidence: 99%

Origin of Orbital Ferromagnetism and Giant Magnetic Anisotropy at the Nanoscale

2006

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“…[12]. Although the magnetization mechanism reported here has an electrostatic origin similar to the one proposed in bulk CaO, new ingredients are present: the localization of the spin moments close to the surface, and the extended character of the polarized 2p valence band states.…”

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confidence: 80%

Magnetism and half-metallicity at the O surfaces of ceramic oxides

Gallego

Beltrán

Cerdá

et al. 2005

J. Phys.: Condens. Matter

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The occurence of spin-polarization at ZrO2, Al2O3 and MgO surfaces is proved by means of abinitio calculations within the density functional theory. Large spin moments, as high as 1.56 µB, develop at O-ended polar terminations, transforming the non-magnetic insulator into a half-metal. The magnetic moments mainly reside in the surface oxygen atoms and their origin is related to the existence of 2p holes of well-defined spin polarization at the valence band of the ionic oxide. The direct relation between magnetization and local loss of donor charge makes possible to extend the magnetization mechanism beyond surface properties.PACS numbers: 75.70. Rf, 73.20.At, When dimensions are reduced to the nanoscale, we are faced to a new understanding of the physical properties of matter: bulk insulators and semiconductors exhibit metallic surfaces [1], non-magnetic materials get spin polarization when forming nanoparticles [2], unstable bulk structures exist in ultrathin film form [3,4], etc. At the origin of these phenomena are the reduced dimensionality and the enhanced role of the surfaces or boundaries in the final properties of the system. Together with its inherent fundamental interest, this has important technological consequences, auspicating the birth of new technologies [5,6]. Special attention is devoted to magnetic low dimensional structures, in particular as sources of spin current in the emerging field of spintronics [5].In this letter, we report on the existence of large magnetic moments and half-metallicity at the O-rich surfaces of ceramic oxides, focusing on ZrO 2 , Al 2 O 3 and MgO. These are non-magnetic ionic insulators widely applied in bulk and thick film form, that have also been grown as ultrathin films and nanometric grains [7]. Their electronic structure can be roughly described as a valence band formed by the filled O 2p orbitals and a conduction band formed by the empty metal levels. When a M x O y unit -M being the metal donor and x,y accounting for the particular metal to oxygen ratio-is broken to form the surface, the loss of coordination of the surface O atoms originates 2p holes in the valence band of the oxide. Our results show that this generates high spin moments at the topmost O layer, which induce magnetization at the adjacent planes and, remarkably, alter the electronic structure of the oxide from insulating to half-metallic.Very recently unexpected ferromagnetism has been measured in thin films of undoped non-magnetic oxides, like HfO 2 and ZrO 2 , possibly assigned to the presence of lattice defects concentrated at the film interface. [8,9]. Here we prove the existence of a magnetization mechanism rooted in the loss of donor charge of the O atoms, something that can also occur in films with cation vacancies. This provides an explanation for the origin of the magnetic moments of these so called 'd-zero' ferromagnets. Furthermore, we predict that this kind of magnetism can be extended to a wider class of non-magnetic oxides, like MgO and Al 2 O 3 , where the cation is not necessarily...

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“…We also find that highly desirable half-metallicity can be achieved in such an electronic structure, which exhibits a strong tunability against gate voltage, strain, and magnetic field. It will be interesting to study thin-films 42,43 and nanowire/nanotube 44 of EuB 6 , which provide a platform for tuning the electronic and magnetic properties via these external stimuli.…”

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confidence: 99%

Spin-split conduction band in EuB6and tuning of half-metallicity with external stimuli

Kim

Lee

et al. 2013

Phys. Rev. B

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We report Eu L3-edge resonant inelastic x-ray scattering (RIXS) investigation of the electronic structure of EuB6. We observe that the RIXS spectral weight around 1.1 eV increases dramatically when the system is cooled below the ferromagnetic ordering temperature and follows the magnetic order parameter. This spectral feature is attributed to the inter-site excitation from the local 4f orbital to the spin-split 5d orbital on the neighboring site, illustrating the essential role of exchange splitting of the conducting electrons. Based on our density functional theory calculations and the RIXS data, EuB6 at low temperature can be consistently described with a semi-metallic electronic structure with incomplete spin-polarization. We propose that half-metallicity in EuB6 can be achieved utilizing the strong tunability of the electronic structure against gate voltage, strain, and magnetic field.

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Magnetism in thin films of CaB6 and SrB6

Cited by 76 publications

References 18 publications

Origin of Orbital Ferromagnetism and Giant Magnetic Anisotropy at the Nanoscale

Origin of Orbital Ferromagnetism and Giant Magnetic Anisotropy at the Nanoscale

Magnetism and half-metallicity at the O surfaces of ceramic oxides

Spin-split conduction band in EuB6and tuning of half-metallicity with external stimuli

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