Hydrogen-plasma-induced magnetocrystalline anisotropy ordering in self-assembled magnetic nanoparticle monolayers

• Alexander Weddemann,
• Judith Meyer,
• Anna Regtmeier,
• Irina Janzen,
• Dieter Akemeier and
• Andreas Hütten

Beilstein J. Nanotechnol. 2013, 4, 164–172, doi:10.3762/bjnano.4.16

• σII = 1.14 nm. According to Hütten et al. [3], the smaller species are superparamagnetic while the larger contain a certain degree of ferromagnetic components. Sample preparation Both samples were prepared in a procedure introduced by Puntes et al. [14] under airless conditions. For the synthesis of

• homogeneously magnetized along their volume. Therefore, each individual particle may be approached by its magnetic moment , with MS being the saturation magnetization of the material, VP the particle volume and the angular components. The equilibrium state of a system of ferromagnetic components is a solution

Sub-10 nm colloidal lithography for circuit-integrated spin-photo-electronic devices

• Adrian Iovan,
• Marco Fischer,
• Roberto Lo Conte and
• Vladislav Korenivski

Beilstein J. Nanotechnol. 2012, 3, 884–892, doi:10.3762/bjnano.3.98

• ][24][25], and consisted of a spin-majority/minority ferromagnetic bi-layer Fe0.7Cr0.3(10 nm)/Fe(15 nm) [25] capped with Cu(10 nm), for spin-population-inversion injection. Even though the deposition technique is not highly directional, we find that the angle of incidence through the 10 nm openings in

• behaviour and showed that the fabricated nanocontact arrays are of high quality. We next demonstrate a point-contact array with the contacts having a magnetic core. More specifically, the core material is a majority/minority ferromagnetic bi-layer of Fe/Fe0.7Cr0.3 [28], where due to the opposite spin

• exchange splitting in the ferromagnetic point contact core (10–100 mV, see [24][25] for more details). Such high-bias, high-density, spin-polarized injection produces large nonequilibrium spin accumulation in the contact core, which allows spin-flip photon-emission transitions, vertical in the momentum of

Highly ordered ultralong magnetic nanowires wrapped in stacked graphene layers

• Abdel-Aziz El Mel,
• Jean-Luc Duvail,
• Eric Gautron,
• Wei Xu,
• Chang-Hwan Choi,
• Benoit Angleraud,
• Agnès Granier and
• Pierre-Yves Tessier

Beilstein J. Nanotechnol. 2012, 3, 846–851, doi:10.3762/bjnano.3.95

• the quality of the nickel nanowires after annealing attributed to a decrease of the roughness of the nickel surface and to a reduction of the defect density. This new type of graphene–ferromagnetic-metal nanowire appears to be an interesting building block for spintronic applications. Keywords

• : carbon; ferromagnetic; graphene; nanofabrication; nanowires; nickel; phase separation; Introduction Magnetic nanowires have been widely investigated during the last two decades for fundamental physics [1][2][3][4][5][6][7], and nano-engineering [7][8][9][10]. The various properties of these

• template methods [1][2][3][4][5][6][7][8][9][10][11][12], ferromagnetic nanowires still suffer from their relatively short length, which cannot reach up to the macroscopic scale. In addition, the manipulation of such one-dimensional (1D) nanostructures is often considered as a complicated process and a

Tuning the properties of magnetic thin films by interaction with periodic nanostructures

• Ulf Wiedwald,
• Felix Haering,
• Stefan Nau,
• Carsten Schulze,
• Herbert Schletter,
• Denys Makarov,
• Alfred Plettl,
• Karsten Kuepper,
• Manfred Albrecht,
• Johannes Boneberg and
• Paul Ziemann

Beilstein J. Nanotechnol. 2012, 3, 831–842, doi:10.3762/bjnano.3.93

• ferromagnetic at room temperature down to a Co concentration of about 15 atom % [34]. MOKE remanence curves were measured by saturating the sample, subsequently applying a reverse field and recording the remanent magnetization (Figure 9). The angle θ of the external magnetic field with respect to the sample

Focused electron beam induced deposition: A perspective

• Michael Huth,
• Fabrizio Porrati,
• Christian Schwalb,
• Marcel Winhold,
• Roland Sachser,
• Maja Dukic,
• Jonathan Adams and
• Georg Fantner

Beilstein J. Nanotechnol. 2012, 3, 597–619, doi:10.3762/bjnano.3.70

• to the next section. Co–Pt FEBID structures As a second example of a binary FEBID experiment recent results on the Co–Pt system are reviewed [33]. The binary phase diagram of Co–Pt features several ferromagnetic intermetallic compounds. The most prominent of these is the L10 phase of CoPt, which has

• electron irradiated sample shows an increase by about two orders of magnitude. The conductivity levels off below 50 K and shows only a small residue of the conductance drop at 12 K. The Hall data indicate now a ferromagnetic state at room temperature with increasing coercive field as the sample is cooled

• to low temperatures. This indicates that the phase transformation from an amorphous to the ordered L10 phase is accompanied by a corresponding phase transition from a superparamagnetic to a moderately hard ferromagnetic state. The overall magnetic properties of these samples depend strongly on the

Strong spin-filtering and spin-valve effects in a molecular V–C₆₀–V contact

• Mohammad Koleini and
• Mads Brandbyge

Beilstein J. Nanotechnol. 2012, 3, 589–596, doi:10.3762/bjnano.3.69

• ]. The C60 molecule is considered as an attractive anchoring group for molecular electronics due to its mechanical robustness [8]. Moreover, the lowest unoccupied molecular orbital (LUMO) of C60 is close to the Fermi level of ferromagnetic elements which makes spin injection relatively easy [9], and

• , ferromagnetic (FM) and anti-ferromagnetic (AFM) spin alignment between atoms of tip and adatom, have been considered. The site on the C60 with the highest binding energy for a V adatom is η5, which is roughly over the center of a pentagon of a C60, and due to the symmetric structure of the C60, this site is

P-wave Cooper pair splitting

• Henning Soller and
• Andreas Komnik

Beilstein J. Nanotechnol. 2012, 3, 493–500, doi:10.3762/bjnano.3.56

• effects. The result is the Hamiltonian where represents the resonant level. Throughout the rest of this exposition we use units in which e = = kB = 1 and restrict ourselves to a quantum dot on resonance Δd = 0. Ferromagnetic electrodes are described in the language of electron field operators Ψk,α,σ

qPlus magnetic force microscopy in frequency-modulation mode with millihertz resolution

• Maximilian Schneiderbauer,
• Daniel Wastl and
• Franz J. Giessibl

Beilstein J. Nanotechnol. 2012, 3, 174–178, doi:10.3762/bjnano.3.18

• Maximilian Schneiderbauer Daniel Wastl Franz J. Giessibl Institute of Experimental and Applied Physics, University of Regensburg, 93040 Regensburg, Germany 10.3762/bjnano.3.18 Abstract Magnetic force microscopy (MFM) allows one to image the domain structure of ferromagnetic samples by probing the

• . Regions of aligned spins, called domains, are used, for example, to store bits of information on hard discs. Such ferromagnetic domains have much larger magnetic dipole moments, as many atoms contribute to the resulting moment. To probe magnetic structures on the atomic as well as on the domain-size scale

• between a tip atom with fixed spin orientation and a sample atom is measured (Figure 1c). Imaging magnetic domains by Magnetic Force Microscopy (MFM) [6][7] is nowadays well-established. MFM images the magnetic-dipole interaction of a ferromagnetic tip and a domain-structured sample (Figure 1a). Typically

Analysis of fluid flow around a beating artificial cilium

• Mojca Vilfan,
• Gašper Kokot,
• Andrej Vilfan,
• Natan Osterman,
• Blaž Kavčič,
• Igor Poberaj and
• Dušan Babič

Beilstein J. Nanotechnol. 2012, 3, 163–171, doi:10.3762/bjnano.3.16

• diameter 55 nm [24]) in water. To prevent aggregation of the beads, we coated them with BSA (bovine serum albumin), 10 mg/mL, for 4 h in an ultrasonic bath. One end of the assembled chain was attached to the surface through prefabricated ferromagnetic-nickel anchoring sites. The nickel dots were

Enhancement of the critical current density in FeO-coated MgB₂ thin films at high magnetic fields

• Andrei E. Surdu,
• Hussein H. Hamdeh,
• Imad A. Al-Omari,
• David J. Sellmyer,
• Alexei V. Socrovisciuc,
• Andrei A. Prepelita,
• Ezgi T. Koparan,
• Ekrem Yanmaz,
• Valery V. Ryazanov,
• Horst Hahn and
• Anatolie S. Sidorenko

Beilstein J. Nanotechnol. 2011, 2, 809–813, doi:10.3762/bjnano.2.89

• that ferromagnets strongly suppress superconductivity, and even a small ferromagnetic region can be a strong pin, as was confirmed in experiments with NbTi wires containing nanometer-sized arrays of Ni pins [9]. We placed the ferromagnetic nanoparticles on the surface, instead of in the volume of the

Interaction of spin and vibrations in transport through single-molecule magnets

• Falk May,
• Maarten R. Wegewijs and
• Walter Hofstetter

Beilstein J. Nanotechnol. 2011, 2, 693–698, doi:10.3762/bjnano.2.75

• an isotropic Heisenberg spin-exchange with the conduction band electron spin where τ is the vector of Pauli matrices. The coupling J is assumed to be anti-ferromagnetic, which, as pointed out in [16], depends on the spins of the virtual charge states of the SMM [17][18]. One might expect that

Distinguishing magnetic and electrostatic interactions by a Kelvin probe force microscopy–magnetic force microscopy combination

• Miriam Jaafar,
• Oscar Iglesias-Freire,
• Luis Serrano-Ramón,
• Manuel Ricardo Ibarra,
• Jose Maria de Teresa and
• Agustina Asenjo

Beilstein J. Nanotechnol. 2011, 2, 552–560, doi:10.3762/bjnano.2.59

• , Spain 10.3762/bjnano.2.59 Abstract The most outstanding feature of scanning force microscopy (SFM) is its capability to detect various different short and long range interactions. In particular, magnetic force microscopy (MFM) is used to characterize the domain configuration in ferromagnetic materials

• such as thin films grown by physical techniques or ferromagnetic nanostructures. It is a usual procedure to separate the topography and the magnetic signal by scanning at a lift distance of 25–50 nm such that the long range tip–sample interactions dominate. Nowadays, MFM is becoming a valuable

• every kind of force to the total force measured leads to serious problems for obtaining quantitative information from the measurements [4]. Among those SFM techniques, magnetic force microscopy (MFM) [5] was developed to characterize the domain configuration of ferromagnetic thin films, rather than the

Nanoscaled alloy formation from self-assembled elemental Co nanoparticles on top of Pt films

• Luyang Han,
• Ulf Wiedwald,
• Johannes Biskupek,
• Kai Fauth,
• Ute Kaiser and
• Paul Ziemann

Beilstein J. Nanotechnol. 2011, 2, 473–485, doi:10.3762/bjnano.2.51

• support easily overwhelms the total magnetic moment of the tiny amount of ferromagnetic material in the NPs. In the present system one can benefit from the paramagnetic response of the Pt(111) film and paramagnetic impurities in MgO compensating the diamagnetic signal of the substrate. Since the

• diamagnetism of MgO is temperature independent and the paramagnetic signal follows Curie’s law at low temperatures [40], compensation can be achieved at an appropriate temperature, which is experimentally determined to be around 29 K for our samples. As the non-ferromagnetic background was strongly reduced, a

Effect of large mechanical stress on the magnetic properties of embedded Fe nanoparticles

• Srinivasa Saranu,
• Sören Selve,
• Ute Kaiser,
• Luyang Han,
• Ulf Wiedwald,
• Paul Ziemann and
• Ulrich Herr

Beilstein J. Nanotechnol. 2011, 2, 268–275, doi:10.3762/bjnano.2.31

• with a straight line and has been subtracted from the data. Note that the total ferromagnetic moment of Fe nanoparticles (8.3·10−6 emu) in saturation is only about 2% of the paramagnetic signal of the Ta substrate at 5000 Oe. At this temperature, the particles show a ferromagnetic behaviour. It should

• observed at 300 K compared to 10 K, there is a small remnant magnetization indicating that at least some of the particles show ferromagnetic behaviour at 300 K. This may be attributed to the presence of a small fraction of larger Fe nanoparticles (as indicated by the size distribution given in Figure 1

Extended X-ray absorption fine structure of bimetallic nanoparticles

• Carolin Antoniak

Beilstein J. Nanotechnol. 2011, 2, 237–251, doi:10.3762/bjnano.2.28

• larger lattice parameters, but all the changes are rather small. Similar trends are reported for other ferromagnetic or antiferromagnetic materials, e.g. for bcc and fcc Fe [95]. Experimentally, the magnetic moments of FePt nanoparticles were found to be reduced with respect to the correspondent bulk

Structural and magnetic properties of ternary Fe_1–xMn_xPt nanoalloys from first principles

• Markus E. Gruner and
• Peter Entel

Beilstein J. Nanotechnol. 2011, 2, 162–172, doi:10.3762/bjnano.2.20

• functional devices. Conclusion: Addition of Mn effectively increases the stability of single crystalline L10 particles over multiply twinned morphologies. This, however, compromises the stability of the ferromagnetic phase due to an increased number of antiferromagnetic interactions. The consequence is that

• effective interlayer coupling and mediates an indirect ferromagnetic (FM) interaction between the adjacent 3d layers, which overrides the smaller direct antiferromagnetic coupling across the Pt layer. The validity of this model has been verified in large scale first principles calculation of a partially

• below for FePt). The ferromagnetic, ordered icosahedron, which is nearly degenerate for Fe265Pt296, has become unstable in the Mn–Pt system for sizes above 147 atoms. During the geometric optimization procedure it transforms downhill to a perfect L10 cuboctahedron. This proves that the Mackay path is a

Structure, morphology, and magnetic properties of Fe nanoparticles deposited onto single-crystalline surfaces

• Armin Kleibert,
• Wolfgang Rosellen,
• Mathias Getzlaff and
• Joachim Bansmann

Beilstein J. Nanotechnol. 2011, 2, 47–56, doi:10.3762/bjnano.2.6

• process might be accompanied by a complex reshaping of the particles. Keywords: epitaxy; iron; magnetic nanoparticles; Ni(111); RHEED; spontaneous self-alignment; STM; W(110); XMCD; Introduction Ferromagnetic clusters and nanoparticles have gained huge interest due to their interesting fundamental

• properties as well as their possible applications in data storage media, chemistry, biotechnology and medicine [1][2][3][4]. First, Stern–Gerlach measurements proved that ferromagnetic particles may exhibit enhanced and strongly size-dependent magnetic moments [5]; and even non-magnetic materials can show

• Experiments on exposed mass-filtered Fe nanoparticles on (ferromagnetic) supports require in situ cluster deposition as well as surface sensitive analysis techniques performed under ultrahigh vacuum conditions. To motivate the need of our combined approach, we first introduce the arc cluster ion source (ACIS

Magnetic interactions between nanoparticles

• Steen Mørup,
• Mikkel Fougt Hansen and
• Cathrine Frandsen

Beilstein J. Nanotechnol. 2010, 1, 182–190, doi:10.3762/bjnano.1.22

• 10.3762/bjnano.1.22 Abstract We present a short overview of the influence of inter-particle interactions on the properties of magnetic nanoparticles. Strong magnetic dipole interactions between ferromagnetic or ferrimagnetic particles, that would be superparamagnetic if isolated, can result in a

• magnetic dipole interactions can have a strong influence on, e.g., the magnetic dynamics in samples containing ferromagnetic or ferrimagnetic nanoparticles. If nanoparticles or thin films are in close proximity, exchange interactions between surface atoms can be significant. An important example of

• magnetic proximity effects is exchange bias, which manifests itself as a shift of the hysteresis curves obtained after field cooling of a ferromagnetic or ferrimagnetic material in contact with an antiferromagnetic material [1][2][3]. This was first observed in nanoparticles consisting of a core of

Magnetic nanoparticles for biomedical NMR-based diagnostics

• Huilin Shao,
• Tae-Jong Yoon,
• Monty Liong,
• Ralph Weissleder and
• Hakho Lee

Beilstein J. Nanotechnol. 2010, 1, 142–154, doi:10.3762/bjnano.1.17

• spin state (typically ferromagnetic or ferrimagnetic). This superparamagnetic property enables MNPs to avoid spontaneous aggregation in solution, a feature that makes them suitable for many biomedical applications. In its simplest form, an MNP is comprised of an inorganic magnetic core and a

• applications. Doped-ferrite nanoparticles The magnetization of ferrite nanoparticles can be further enhanced by doping the ferrite with ferromagnetic elements such as manganese (Mn), cobalt (Co) or nickel (Ni) [23][27][45]. Among the singly-doped ferrite MNPs, MnFe2O4 nanoparticles were found to exhibit the

Ultrafine metallic Fe nanoparticles: synthesis, structure and magnetism

• Olivier Margeat,
• Marc Respaud,
• Catherine Amiens,
• Pierre Lecante and
• Bruno Chaudret

Beilstein J. Nanotechnol. 2010, 1, 108–118, doi:10.3762/bjnano.1.13

• temperature. The gyromagnetic ratio measured by ferromagnetic resonance is of the same order as that of bulk Fe, which allows us to conclude that the orbital and spin contributions increase at the same rate. A large magnetic anisotropy for metallic Fe has been measured up to (3.7 ± 1.0)·105 J/m3. Precise

• ferromagnetic metals [1][2][3][4]. More surprisingly, the study of small Rh NPs revealed a paramagnetic to ferromagnetic phase transition induced by size reduction for clusters containing less than 40 atoms [5]. Band structure calculations have investigated the role of size reduction and demonstrated that it

• ferromagnetic 3d metals. In the case of free-standing Fe clusters, Billas and coworkers have demonstrated the enhancement of the magnetic moment µFe when the cluster contains less than 1000 atoms [2][3]. In this size range some oscillations of µFe with cluster size have also been revealed. Similarly, supported

Magnetic coupling mechanisms in particle/thin film composite systems

• Giovanni A. Badini Confalonieri,
• Philipp Szary,
• Durgamadhab Mishra,
• Maria J. Benitez,
• Mathias Feyen,
• An Hui Lu,
• Leonardo Agudo,
• Gunther Eggeler,
• Oleg Petracic and
• Hartmut Zabel

Beilstein J. Nanotechnol. 2010, 1, 101–107, doi:10.3762/bjnano.1.12

• cooled, implying that its origin should be ascribed to an antiferromagnetic/ferromagnetic (AF/FM) coupling [31][32][33][34][35]. The magnetic exchange interaction between an AF and an FM layer can usually be observed as a horizontal shift of the magnetic hysteresis loop, when cooling the material from a

• ferrimagnetic maghemite NPs and a ferromagnetic Co thin film, it is necessary to account for the presence of an extra AF component. A possible explanation is that the Co layer is partially oxidized to AF CoO. The Co layer is capped with a protective Cu layer, and therefore, oxidation is more likely to occur at

Review and outlook: from single nanoparticles to self-assembled monolayers and granular GMR sensors

• Alexander Weddemann,
• Inga Ennen,
• Anna Regtmeier,
• Camelia Albon,
• Annalena Wolff,
• Katrin Eckstädt,
• Nadine Mill,
• Michael K.-H. Peter,
• Jochen Mattay,
• Carolin Plattner,
• Norbert Sewald and
• Andreas Hütten

Beilstein J. Nanotechnol. 2010, 1, 75–93, doi:10.3762/bjnano.1.10

• response to an external magnetic field resembles the Langevin behavior of paramagnetic materials but with the high susceptibility and magnetization values of the ferromagnetic materials they are composed of, compare Figure 7. With even smaller particles, surface effects become dominant and a fully quantum

• ferromagnetic particles mutually align their magnetic dipole moments which entails an attractive coupling and may result in different geometrical patterns such as particle chains or rings [55][56]. An example of a dipole interaction dominated arrangement is shown in Figure 10(a): Co particles with a bimodal

• structured sample, a suspension of ferromagnetic particles can be placed on the substrate in the presence of an external magnetic field. For manufacturing of particle layers, a homogeneous magnetic field needs to be employed; inhomogeneous fields result in the accumulation of nanoparticles along the area

Uniform excitations in magnetic nanoparticles

• Steen Mørup,
• Cathrine Frandsen and
• Mikkel Fougt Hansen

Beilstein J. Nanotechnol. 2010, 1, 48–54, doi:10.3762/bjnano.1.6

• of the magnetization in nanoparticles. In this paper we give a short review of the spin dynamics in non-interacting nanoparticles below the blocking temperature. Ferromagnetic and ferrimagnetic nanoparticles First, we consider a ferromagnetic or ferrimagnetic material with cubic crystal structure and

• difference between adjacent spin wave states is small and the quantized states are well approximated by a continuous distribution of energies. Furthermore, the magnetic anisotropy is usually neglected in the calculations [9][10]. In ferromagnetic and ferrimagnetic materials at low temperatures, spin wave

Preparation and characterization of supported magnetic nanoparticles prepared by reverse micelles

• Ulf Wiedwald,
• Luyang Han,
• Johannes Biskupek,
• Ute Kaiser and
• Paul Ziemann

Beilstein J. Nanotechnol. 2010, 1, 24–47, doi:10.3762/bjnano.1.5

• , saturation magnetizations, and Curie temperatures. Technologically important is the report of the last noted group, that after annealing of FePt NPs as small as 4 nm, ferromagnetic behavior is observed even at ambient temperature corresponding to magnetic anisotropies close to those of the bulk material [52

• already mentioned in the introduction, a vast variety of preparation approaches have been developed and more or less successfully tested for their application to fabricate ferromagnetic metal NPs. Success, in this context, may not be an appropriate term, since it critically hinges on the specific