Critical behaviour of nanoparticles

Pseudocritical behavior of ferromagnetic pure and random diluted nanoparticles with competing interactions: Variational and Monte Carlo approaches.
E. A. Velásquez, J. Mazo-Zuluaga, J. Restrepo, and Òscar Iglesias

Phys. Rev. B.83,184432 (2011)

Particle with diameter D = 10 having 1067 atoms

and bcc structure. Atoms with different coord. #

are colored differently.

Dependence of the ordering temperature
on diameter for Ni nanostructures.

Spin pumping by excited magnons

Spin Pumping by Parametrically Excited Exchange Magnons. 
C. W. Sandweg, Y. Kajiwara, A. V. Chumak, A. A. Serga, V. I. Vasyuchka, M. B. Jungfleisch, E. Saitoh, and B. Hillebrands
Phys. Rev. Lett. 106, 216601 (2011)

Viewpoint: Spin-magnon transmutation.
Gerrit E. Bauer, Yaroslav Tserkovnyak
Physics.4.40 (2011)

Generation of a magnon  by the spin-transfer torque.

Dipolar spin-ice on the kagomé

Two-Stage Ordering of Spins in Dipolar Spin Ice on the Kagome Lattice.
Gia-Wei Chern, Paula Mellado, and O. Tchernyshyov
Phys. Rev. Lett.106,.207202 (2011)

 Magnetic configurations of the dipolar kagome ice and their alternative representations. (a) A spin-ice microstate lacking spin order but possessing charge order. The latter is manifested in the dumbbell representation (b). (c) One of the ground states exhibiting the magnetic order and its depiction in terms of dimers (d) . Monte Carlo results of specific heat and entropy signalign the PM/spin-ice, charge-order and spin-order transitions as T decreases.

DW motion by Rashba effect

Fast current-induced domain-wall motion controlled by the Rashba effect.
Ioan Mihai Miron, Thomas Moore, Helga Szambolics, Liliana Daniela Buda-Prejbeanu, Stéphane Auffret, Bernard Rodmacq, Stefania Pizzini, Jan Vogel, Marlio Bonfim, Alain Schuhl and Gilles Gaudin.
Nature Mater.10, 419 (2011)

Effects of magnetic field and electric current on DWs.

MQT of spin chirality in molecular clusters

Macroscopic quantum dynamics of toroidal moment in Ising-type rare-earth clusters.
D. I. Plokhov, A. K. Zvezdin, A. I. Popov
Phys. Rev. B 83, 184415 (2011)

Rabi-type oscillations between states.

EB in multiferroic NPs

Exchange bias in BiFe0.8Mn0.2O3 nanoparticles with an antiferromagnetic core and a diluted antiferromagnetic shell.
P. K. Manna and S. M. Yusuf, R. Shukla and A. K. Tyagi
Phys. Rev. B 83, 184412 (2011)

(a) ZFC and FC under 1-T cooling field curves at 5K, (b) Same as (a) under
5-T cooling field, (c) Cooling field dependence of the horizontal (Heb) and vertical (Meb) loop shifts.

Magneric dipoles in a plane

Kosterlitz-Thouless transition of magnetic dipoles on the two-dimensional plane.
Seung Ki Baek, Petter Minnhagen, and Beom Jun Kim
Phys. Rev. B 83, 184409 (2011) 

Staggered magnetization and susceptibility for squared (left) and honeycomb (right) lattices.

Spin-transfer dynamics of a DW

Dynamics of domain wall driven by spin-transfer torque.
P. Chureemart, R. F. L. Evans, and R. W. Chantrell
Phys. Rev B 83, 184416 (2011)

The critical spin-transfer-torque field for different temperatures.

The time-dependent variation of the domain-wall displacement for different current-induced magnetic fields at T=0.

Nanostructure of magnetic monopole defects

Nanoscale structure of the magnetic induction at monopole defects in artificial spin-ice lattices.
C. Phatak, A. K. Petford-Long, O. Heinonen, M. Tanase, and M. De Graef
Phys. Rev. B 83, 174431 (2011)

Magnetic induction color maps reconstructed after (a) the first demagnetization cycle, showing the formation
of defect strings and two magnetic monopole defects, and (b) after the second demagnetizing loop.

Vortex mode splitting due to dipolar interactions in disks

Dynamics of Coupled Vortices in a Pair of Ferromagnetic Disks.
Satoshi Sugimoto, Yasuhiro Fukuma, Shinya Kasai, Takashi Kimura, Anjan Barman, and YoshiChika Otani
Phys. Rev. Lett. 106, 197203 (2011)

(a) Experimental setup. (b) Frequency dependence of the normalized dc voltage Vdc=Iac measured for an isolated disk (green triangles) and for the paired disks with different polarities; black squares for p1p2= 1, and red circles for p1p2=-1.

All optical magnetization reversal in Gd

Hot-Electron-Driven Enhancement of Spin-Lattice Coupling in Gd and Tb 4f Ferromagnets Observed by Femtosecond X-Ray Magnetic Circular Dichroism.
Marko Wietstruk, Alexey Melnikov, Christian Stamm, Torsten Kachel, Niko Pontius, Muhammad Sultan, Cornelius Gahl, Martin Weinelt, Hermann A. Dürr, and Uwe Bovensiepen.

Phys. Rev. Lett. 106, 127401 (2011)

Time-dependent XMCD signals for Gd (top) and Tb (bottom) measured by 10 ps x-ray probe and 50 fs
laser pump pulses.

Plasmonic nanostructures

Building plasmonic nanostructures with DNA.
Shawn J. Tan, Michael J. Campolongo, Dan Luo & Wenlong Cheng
Nature Nanotechnology 6, 268 (2011)

Schematic of plasmonic nanostructures assembled from libraries of plasmonic atoms with various DNA motifs.

Magnets tackle kinetic questions

Biosensors: Magnets tackle kinetic questions.
Shawn P. Mulvaney
Nature Nanotechnology 6, 266 (2011)

Quantification of protein interactions and solution transport using high-density GMR sensor arrays
Richard S. Gaster, Liang Xu, Shu-Jen Han , Robert J. Wilson , Drew A. Hall , Sebastian J. Osterfeld , Heng Yu ,and Shan X. Wang
Nature Nanotechnology 6, 314 (2011)

GMR sensors can also be used to detect biomolecules that have been labelled with magnetic beads (left). Here one of the four antibodies (blue) attached to a magnetic bead (red) binds to a protein antigen (yellow) immobilized on top of a GMR sensor in a proteomic microarray. The change in the resistance of the GMR wire caused by the magnetic field of the bead allows the kinetics of the protein–antibody interaction to be studied.

Finite-size and surface effects in NPs

Finite size and surface effects on the magnetic properties of cobalt ferrite nanoparticles.
C. Vázquez-Vázquez, M. A. López-Quintela, M. C. Buján-Núñez and J. Rivas
 J. Nanoparticle Research 13, 1663 (2011)

(a) Thermal dependence of a the anisotropy constant, K,and (b) the saturation magnetization, MS, for the different
CoFe2O4 samples.

Excitations in Core/shell NPs

Low-energy magnetic excitations in Co/CoO core/shell nanoparticles.
M. Feygenson, X. Teng, S. E. Inderhees, Y. Yiu, W. Du, W. Han, J. Wen, Z. Xu, A. A. Podlesnyak, J. L. Niedziela, M. Hagen, Y. Qiu, C. M. Brown, L. Zhang, and M. C. Aronson.
Phys. Rev. B 83, 174414 (2011)

(a) The q-integrated scattered intensity I (E) at different temperatures for Co/CoO nanoparticles. Dashed lines indicate the onset of antiferromagnetic order at TN and the dynamical blocking of the Co cores at the blocking temperature
TB. (b) Energy dependence of χ(E) for a constant wave-vector cut 0.12 °A−1 wide and centered at q = 1.27 °A−1 (c) The scattered intensity I (q,E) at 150 K. Dark curved lines are shadows from the radial collimator.

Self-assembled FeO NP arrays

Structural and magnetic characterization of self-assembled iron oxide nanoparticle arrays.
M J Benitez, D Mishra, P Szary, G A Badini Confalonieri, M Feyen, A H Lu, L Agudo, G Eggeler, O Petracic and H Zabel
J. Phys.: Condens. Matter, 23 126003 (2011)

(a), (b) TEM images of as-prepared iron oxide NPs with a diameter of 20 nm. SEM images of (c) a multilayer and (d) a monolayer of NPs on Si substrates dried at 80 ◦C and (e) a multilayer and (f) a monolayer of NPs annealed at 230 ◦C in vacuum, respectively.

Size-Dependent Spin Structures in NPs

Size-Dependent Spin Structures in Iron Nanoparticles.
A. Fraile Rodríguez, A. Kleibert, J. Bansmann, A. Voitkans, L. J. Heyderman, and F. Nolting
Phys. Rev. Lett. 104, 127201 (2010)

(a) Size dependence of the absolute value of the in-plane canting angles between the film and the
upper particle magnetization. White dots: experimental data. Solid and dashed: calculated curves for two values of Ku.    (b) Sketch of the spin structure of a Wulff-shaped 10-nm particle and Ku=50 10-6eV=atom. (c) Size dependence of
the experimental spread.

Magnetic hysteresis of individual NPs

Element-Specific Magnetic Hysteresis of Individual 18 nm Fe Nanocubes
Florian Kronast, Nina Friedenberger, Katharina Ollefs, Sebastian Gliga, Logane Tati-Bismaths, Ronja Thies, Andreas Ney, Ramona Weber, Christoph Hassel, Florian M. Romer, Anastasia V. Trunova, Christian Wirtz, Riccardo Hertel, Hermann A. Dürr, and Michael Farle 
Nano Lett. 11, 1710 (2011)

Magnetic imaging and spectromicroscopy of individual Fe
nanocubes in an applied magnetic field of up to 33 mT.

Finite-size effects in NPs characterized by correlations

Spin-spin correlations in ferromagnetic nanosystems.
E. Y. Vedmedenko, N. Mikuszeit, T. Stapelfeldt, R. Wieser, M. Potthoff, A. I. Lichtenstein and R. Wiesendanger

European Physical Journal B,Volume 80, 331 (2011)

Model G(r) as obtained by fitting the parameters to results of MC simulations.
(a) Temperature dependence of the virtual distance r_v.
(b) Virtual correlation length ε(T).
(c) G(r) as a function of r and T. The temperatures
∞ > TC(∞) > TC(L) > Tb(L) > 0 are highlighted.