Friday 30 March 2012

Chirality in artificial spin ice

Emerging Chirality in Artificial Spin Ice.
W. R. Branford, S. Ladak, D. E. Read, K. Zeissler, L. F. Cohen
Science 335, 1597 (2012)
Magnetic vertex configurations and equilibrium phase diagram for artificial spin ice honeycombs. The background (A to D) is a SEM of a small section of the array. (A) The magnetic charge ±q = ±m/l dumbbell representation of a magnetic moment m of length l on a honeycomb of lattice parameter a. Deviations from ideal Ising behavior are characterized by ε = 1 – l/a. (B) Charges on neighboring dumbbells reside on the circumference of a circle of diameter εa. This is equivalent to (C) a point charge Q = Σq and a vertex dipole moment (VDM) of magnitude εaΔq/2 colocated at the vertex center. (Δq = qmax qmin at the vertex.) In connected arrays, the local magnetic structure at the vertex minimizes the VDM (21). (D) The eight possible configurations of magnetic moments (black arrows) at a kagome spin ice vertex. Vertices a to f obey the ice rule and have Q = ±q; VDM = εaq (purple arrows) and spin chirality Ω = –1/3; vertices g and h are ice rule defects with Q = ±3q; VDM = 0 and Ω = +1 (21). (E) The predicted phase diagram for artificial spin ice honeycombs (6, 8) (only the Ice I phase is observed in zero-field). There are four distinct phases: the gas-like Ising paramagnet; the liquid-like short-range spin ice (Ice I) phase; the long-range spin ice (Ice II) phase where the near order extends to second nearest neighbor macrospins, giving favored vertex pairs [ab], [cd], and [ef]; and the long-range ordered macrospin solid state.

DW on helical magnets

Vortex Domain Walls in Helical Magnets.
Fuxiang Li, T. Nattermann, and V. L. Pokrovsky
Phys. Rev. B 108, 107203 (2012)
DWs in centrosymmetric helical magnets. Cross section parallel to the x-y plane of (a) a Hubert wall, (b) a vortex wall parallel to the helical axis in a system where the magnetization rotates in the x-y plane, (c) a vortex wall tilted
with respect to the helical axis.

Review on topological effects on nanomagnetism

Topological effects in nanomagnetism: from superparamagnetism to chiral quantum solitons.
Hans-Benjamin Braun

Advances in Physics 61, 1 (2012)

Chirality switching of a vortex DW

Chirality switching and propagation control of a vortex domain wall in ferromagnetic nanotubes.
J. A. Otálora, J. A. López-López, P. Vargas, and P. Landeros
Appl. Phys. Lett. 100, 072407 (2012)
Illustration of a h2h VDW in MNTs. Counterclockwise (p = 0) and clockwise (p =pi) are the possible vortex chiralities. The magnetization components can be expressed through the angles theta and p, and the main properties of the DW are cast by the position in the z axis, the wall width w, and the DW magnetization angle p.

Transport of a SP bead by DWs

Dynamics of superparamagnetic microbead transport along magnetic nanotracks by magnetic domain walls.
Elizabeth Rapoport and Geoffrey S. D. Beach
Appl. Phys. Lett. 100, 082401 (2012)
Micromagnetically computed DW structure in a 400nm wide, 40 nm thick Permalloy track, with schematic of trapped bead and relevant forces during translation in a fluid. Magnetostatic potential energy versus lateral position is shown for a bead at the track surface with radius (b) 50 nm and (c) 1000 nm.

Dipolar interactions of NP in cells

Modeling magnetic nanoparticle dipole-dipole interactions inside living cells.
Michael Lévy, Florence Gazeau, Jean-Claude Bacri, Claire Wilhelm, and Martin Devaud

Phys. Rev. B 84, 075480 (2011)
Model of spherical lysosome with a magnetization Mlys under an applied magnetic field B0. The Lorentz cavity around a particular (SP) NP (in dark) is displayed and the surface currents I and i on the surface of the lysosome and of the cavity, respectively, are also represented.
Take a look also to the related articles by the same group:

Nanomagnetism reveals the intracellular clustering of iron oxide nanoparticles in the organism.
Michael Levy , Claire Wilhelm , Nathalie Luciani , Vanessa Deveaux , François Gendron , Alain Luciani , Martin Devaud and Florence Gazeau
Nanoscale 3, 4402 (2011)

Long term in vivo biotransformation of iron oxide nanoparticles.
Michael Levy, Nathalie Luciani, Damien Alloyeau, Dan Elgrabli, Vanessa Deveaux, Christine Pechoux, Sophie Chat, Guillaume Wang, Nidhi Vats, François Gendron,Cécile Factor, Sophie Lotersztajn, Alain Luciani, Claire Wilhelm, Florence Gazeau
Biomaterials 32, 3988 (2011)

3D observation of DWs in NiO by XMCD

Three-dimensional spin orientation in antiferromagnetic domain walls of NiO studied by x-ray magnetic linear dichroism photoemission electron microscopy.
Kuniaki Arai, Taichi Okuda, Arata Tanaka, Masato Kotsugi, Keiki Fukumoto, Takuo Ohkochi, Tetsuya Nakamura, Tomohiro Matsushita, Takayuki Muro, Masaki Oura, Yasunori Senba, Haruhiko Ohashi, Akito Kakizaki, Chiharu Mitsumata, and Toyohiko Kinoshita
Phys. Rev. B 85, 104418 (2012)
(a) XMLD-PEEM image in a single T domain. Three S domains, S1, S2, and S3, are observed. (b) Line profile of the solid line shown in (a). This corresponds to the contrast along S1 to S2 to S3. (c) Spin structures estimated from the contrast in (a). The spin axes gradually change from S1 to S2 to S3.

Wednesday 28 March 2012

Limits on data storage based on thermal error

Thermally induced error: Density limit for magnetic data storage.
R. F. L. Evans, R. W. Chantrell, U. Nowak, A. Lyberatos, and H.-J. Richter
Appl. Phys. Lett. 100, 102402 (2012)
Schematic of the “quadrilemma” of magnetic recording. The decrease of grain volume requires an increase in the anisotropy constant K for thermal stability and also maximisation of the saturation magnetisation Ms to ensure thermal writability.

Magnetic particle imaging

X-Space MPI: Magnetic Nanoparticles for Safe Medical Imaging.
Patrick William Goodwill, Emine Ulku Saritas, Laura Rose Croft,Tyson N. Kim, Kannan M. Krishnan, David V. Schaffer, Steven M. Conolly
Advanced Materials Early view (2012)
Magnetic particle imaging (MPI) is an emerging medical imaging technique that could be a safer alternative to X-ray and CT using iodinated contrast agents, especially for patients with chronic kidney disease. Here we describe the overall technique, detail the latest advances in MPI theory, and discuss the optimal nanoparticle characteristics for MPI. We also show images taken using our latest MPI hardware, demonstrating MPI's already superb contrast and high sensitivity.

Artificial Frustrated Systems

The New Journal of Physics has opened a new Focus section on Artificial Frustrated Systems edited by
John Cumings, Laura Jane Heyderman, Christopher Marrows, Robert Stamps 
Focus on Artificial Frustrated Systems

The special section includes a growing collection of articles that will be published during 2012. Up to now it includes  the following:


Gibbsianizing nonequilibrium dynamics of artificial spin ice and other spin systems
Paul E Lammert, Vincent H Crespi and Cristiano Nisoli 
2012 New J. Phys. 14 045009
A network model for field and quenched disorder effects in artificial spin ice
 Zoe Budrikis, Paolo Politi and R L Stamps2012 New J. Phys. 14 045008

Dynamics of artificial spin ice: a continuous honeycomb network 
Yichen Shen, Olga Petrova, Paula Mellado, Stephen Daunheimer, John Cumings and Oleg Tchernyshyov 
2012 New J. Phys. 14 035022

On thermalization of magnetic nano-arrays at fabrication 
Cristiano Nisoli
 2012 New J. Phys. 14 035017
 
Magnetic dipole configurations in honeycomb lattices: order and disorder 
Alexandra Schumann, Philipp Szary, Elena Y Vedmedenko and Hartmut Zabel
2012 New J. Phys. 14 035015

Domain dynamics and fluctuations in artificial square ice at finite temperatures 
Z Budrikis, K L Livesey, J P Morgan, J Akerman, A Stein, S Langridge, C H Marrows and R L Stamps
2012 New J. Phys. 14 035014

Melting artificial spin ice
 Vassilios Kapaklis, Unnar B Arnalds, Adam Harman-Clarke, Evangelos Th Papaioannou, Masoud Karimipour, Panagiotis Korelis, Andrea Taroni, Peter C W Holdsworth, Steven T Bramwell and Björgvin Hjörvarsson
2012 New J. Phys. 14 035009

Multi-step ordering in kagome and square artificial spin ice 
C J Olson Reichhardt, A Libál and C Reichhardt
2012 New J. Phys. 14 025006

Thermodynamics of elementary excitations in artificial magnetic square ice 
R C Silva, F S Nascimento, L A S Mól, W A Moura-Melo and A R Pereira
2012 New J. Phys. 14 015008

Magnetic reversal of an artificial square ice: dipolar correlation and charge ordering 
J P Morgan, A Stein, S Langridge and C H Marrows
2011 New J. Phys. 13 105002

Skyrmion lattice generated by DM interaction

Effect of anisotropy and dipole interaction on long-range order magnetic structures generated by Dzyaloshinskii–Moriya interaction
H.Y. Kwon, K.M. Bu,Y.Z Wu, C. Won
J. Magn. Magn. Mater. 324, 2171 (2012)
(a) Magnetic structure of the stripe domain and (b) skyrmion lattice domain. The black-and-white scales show the out-of-plane part of the magnetization and the arrows show the in-plane part of the magnetization of a grid at the location of the arrows. (c) Change of magnetic structure with increasing external field. The field strength is 0.0, 0.2, 0.4, 0.6, and 0.9J/ς2 from left to right.

Magnetic cactus

Static and Dynamical Phyllotaxis in a Magnetic Cactus.
Cristiano Nisoli, Nathaniel M. Gabor, Paul E. Lammert, J. D. Maynard, and Vincent H. Crespi
Phys. Rev. Lett. 102, 186103 (2009)
A specimen of Mammillaria elongata displaying a helical morphology ubiquitous to nature, a magnetic cactus of dipoles on stacked bearings, and a schematic of a wrapped Bravais lattice showing the angular offset (screw angle) and the axial separation a between particles.

Tuesday 27 March 2012

Magnonics in antidots with perpendicular magnetization

High-symmetry magnonic modes in antidot lattices magnetized perpendicular to the lattice plane
R. Bali, M. Kostylev, D. Tripathy, A. O. Adeyeye, and S. Samarin
Phys. Rev. B 85, 104414 (2012)
Calculated modal profiles for modes MF, M1, M2, and M3 from Figs. 2 and 3.

Unexpected EB in La manganite films

Exchange-bias effect at La0.75Sr0.25MnO3/LaNiO3 interfaces
J. C. Rojas Sánchez, B. Nelson-Cheeseman, M. Granada, E. Arenholz, and L. B. Steren
Phys. Rev. B 85, 094427 (2012)
(a) Ni L2,3 and (b) Mn L2,3 XAS and XMCD spectra for LSMO tLSMO/LNO 8nm/LSMO//STO trilayers with (dash) tLSMO = 2.2 nm, (dot) tLSMO = 4.2nmand(solid) tLSMO = 8.1 nmrespectively. (c)Ni and (d)Mn normalized XMCD asymmetry vs. magnetic field.

Dynamic hysteresis of ferromagnetic NPs

Damping dependence in dynamic magnetic hysteresis of single-domain ferromagnetic particles
H. El Mrabti, P. M. Déjardin, S. V. Titov, and Yu. P. Kalmykov
Phys. Rev. B 85, 094425 (2012)
DMH loops [m(t ) = MH (t )/MS vs h(t ) = (ξ/2σ) cos ωt] at quasistatic and intermediate frequencies for various values of the damping parameter α.

Monday 26 March 2012

Skyrmions in magnets

Here is a collection of articles on skyrmions in magnets, an increasingly hot topic:

1) Spontaneous skyrmion ground states in magnetic metals.
U. K. Rös zligler, A. N. Bogdanov and C. Pfleiderer
Nature 442, 797 (2006)
Three chiral modulated structures for noncentrosymmetric ferromagnets and comparison of their energy density.
2) Spin chirality on a two-dimensional frustrated lattice.
Daniel Grohol, Kittiwit Matan, Jin-Hyung Cho, Seung-Hun Lee, Jeffrey W. Lynn, Daniel G. Nocera and Young S. Lee
Nature Materials 4, 323 (2005)
Measurements of the field-induced transition to a state with non-zero scalar chirality.
3) Skyrmion lattice in a two-dimensional chiral magnet.
Jung Hoon Han, Jiadong Zang, Zhihua Yang, Jin-Hong Park, and Naoto Nagaosa 
Phys. Rev. B 82, 094429 (2010)
(a) A typical Skyrme-crystal spin configuration given by Eq. 19 with B=D2 /J, with the optimized lattice spacing lH= 3/ 2. (b) Skyrme-crystal spin configuration obtained by Monte Carlo method from the lattice spin model

4) Skyrmions and anomalous Hall effect in a Dzyaloshinskii-Moriya spiral magnet.
Su Do Yi, Shigeki Onoda, Naoto Nagaosa, and Jung Hoon Han
Phys. Rev. B 80, 054416 (2009)
A plot of the spin configuration projected on the xy plane Si x ,Si y in the three spin crystal ground states: a SC1 at A2 ,H = 2.0, 0.0 , b SC2 at A2 ,H = 3.0, 0.0 , and cSCh at A2 ,H = 0.0, 2.0 . At the bottom left of each figure are the plots of the Bragg intensity Sk 2 showing two SC1,SC2 and three SCh sets of modulation vectors. Shown at the bottom right
are the plots of the local chirality r. Bright dark regions correspond to Skyrmions anti-Skyrmions

.
5) Condensed-matter physics: Single skyrmions spotted.
Christian Pfleiderer, Achim Rosch
 Nature 465, 880 (2010) N&V

When an electron moves through a special type of magnetic texture called a skyrmion, its magnetic moment (spin) twists to adjust to the skyrmion's local spin structure (ribbon-like pattern). This twisting changes the electron's direction of travel and pushes the electron and the skyrmion in opposite directions (not shown).

Real-space observation of a two-dimensional skyrmion crystal.
X. Z. Yu, Y. Onose, N. Kanazawa, J. H. Park, J. H. Han, Y. Matsui, N. Nagaosa, Y. Tokura
Nature 465, 09124 (2010)

Topological spin textures in the helical magnet Fe0.5Co0.5Si. a, b, Helical (a) and skyrmion (b) structures predicted by Monte Carlo simulation. c, Schematic of the spin configuration in a skyrmion. d–f, The experimentally observed real-space images of the spin texture, represented by the lateral magnetization distribution as obtained by TIE analysis of the Lorentz TEM data: helical structure at zero magnetic field (d), the skyrmion crystal (SkX) structure for a weak magnetic field (50 mT) applied normal to the thin plate (e) and a magnified view of e (f).

6) Giant Skyrmions Stabilized by Dipole-Dipole Interactions in Thin Ferromagnetic Films.
Motohiko Ezawa
Phys. Rev. Lett. 105, 197202 (2010)
(a) Illustration of a giant Skyrmion ( 1 m) in a thin ferromagnetic film. The simplest spin texture has naturally a nontrivial Pontryagin number. It can be created by applying femtosecond optical pulse irradiation focused on a micrometer spot and thus destroying the magnetic order locally. (b) Illustration of magnetic flux lines around a Skyrmion due to magnetic dipoles. When the magnetic order is destroyed locally, a new order is generated which is opposite to that of the environs, so that the magnetic flux closes by itself as short as possible.



7) Comment to previous article.
N. S. Kiselev, A. N. Bogdanov, R. Schäfer, and U. K. Rößler
Phys. Rev. Lett. 107, 179701 (2011)

8) Spin waves in a skyrmion crystal.
Olga Petrova and Oleg Tchernyshyov
Phys. Rev. B.84. 214433 (2011)


9) Chiral skyrmions in thin magnetic films: new objects for magnetic storage technologies?
N S Kiselev, A N Bogdanov, R Schäfer and U K Rößler

J. Phys. D 44, 392001 (2011)
The magnetic phase diagram in reduced variables κ and applied magnetic field H/Ha for fixed values of Q and the reduced layer thickness l indicate the existence region of isolated skyrmions.In the double-hatched area spatially modulated phases (helicoids and skyrmion lattices) correspond to the equilibrium state of the film.


10) Spontaneous atomic-scale magnetic skyrmion lattice in two dimensions.
Stefan Heinze, Kirsten von Bergmann, Matthias Menzel , Jens Brede , André Kubetzka, Roland Wiesendanger, Gustav Bihlmayer and Stefan Blügel
Nature Physics 7, 2045 (2011)
The nanoskyrmion lattice of the Fe ML on Ir(111). a, Sketch of the nanoskyrmion lattice: cones represent atoms of the hexagonal Fe layer and point along their magnetization directions; red and green represent up and down magnetization components, respectively. b, Atomic-resolution STM image of the pseudomorphic hexagonal Fe layer at an Ir step edge. Upper inset: The FT. Lower inset: A side view of the system (tunnel parameters UDC5 mV, ID30 nA). c, SP-STMimage of the Fe ML on Ir(111) with a magnetic tip sensitive to the out-of-plane component of magnetization (Fe-coatedWtip, BDC2 T along the tip axis, UDC50 mV, ID0:5 nA): bright (dark) spots indicate areas with magnetization parallel (antiparallel) to the tip magnetization. Left inset: Simulated SP-STMimage of the nanoskyrmion with out-of-plane magnetic tip. Right inset: FT of the experimental SP-STMimage shown in the two-dimensional Brillouin zone.

11) ChiralityWaves in Two-Dimensional Magnets.
D. Solenov, D. Mozyrsky, and I. Martin
Phys. Rev. Lett. 108,096403 (2012)
(a-e) The optimal magnetic state S(r)=(sinKy cosKx, cosKy, sinKy sinKx) realized at small Kondo coupling, J=   1. Panels (a)-(c) show the spatial dependence of the three magnetization components. (d) Full 3D magnetization pattern. (e) The in-plane magnetization has a ‘‘vortexantivortex’’ structure (vortex points are marked with circles, antivortex points—with squares). The superimposed density plot in e represents scalar chirality. (f ) 1D cut showing the chirality density and the induced charge current density in the lowest energy state,S(r) for J ¼ 0:2 and ¼ 0:5. (g), (h) The 2D periodic magnetization patterns can be naturally mapped onto toroidal surface representing the real-space magnetic unit cell. A simple spiral texture, (g), is unstable with respect to configuration (h) that corresponds to the S(r) texture.

Multiferroics and Toroidal moments in magnets

Some articles on the currently active issue of Mutiferroics and toroidal moments in magnets:

1) Multiferroicity: the coupling between magnetic and polarization orders (A Review).
K.F. Wangab, J.-M. Liuab and Z.F. Renc
Advances in Physics 58, 321(2009)

2) Hypertoroidal moment in complex dipolar structures.
S. Prosandeev, L. Bellaiche
J. Mater. Sci. 44, 5235 (2009)

3) A system exhibiting toroidal order.
A. B. Harris
Phys. Rev. B 82, 184401 (2010)

4) Towards a microscopic theory of toroidal moments in bulk periodic crystals.
Claude Ederer, and Nicola A. Spaldin
Phys. Rev. B B 76, 214404 (2007)

Friday 23 March 2012

Surface stability of maghemite by Cu shell

Increased surface spin stability in  gamma-Fe2O3 nanoparticles with a Cu shell.R D Desautels, E Skoropata, Y-Y Chen, H Ouyang, J W Freeland and J van Lierop
J. Phys.: Condens. Matter 24, 146001 (2012)
(a) Temperature dependence of the Fe magnetization determined from the TEY XMCD signaland the Cu2C interface coating magnetization from the TFY XMCD signal. Cu(0.5 nm)/Fe2O3 and Cu(1.0 nm)/Fe2O3 NPs (b) Temperature dependence of the Fe A- and B-site magnetization.

Hidding from magnetic fields

Experimental Realization of a Magnetic Cloak.
Fedor Gömöry, Mykola Solovyov, Ján Šouc, Carles Navau, Jordi Prat-Camps, Alvaro Sanchez
Science 335, 1466 (2012)
The ferromagnet attracts magnetic field lines (left), the superconductor repels magnetic field lines (middle), and the superconductor-ferromagnetic bilayer cloaks a magnetic field (right). An object inside the cloak would be magnetically undetectable.

Thursday 22 March 2012

Pyrochlore quantum spin ice?

Is the Yb2Ti2O7 pyrochlore a quantum spin ice?
R. Applegate, N. R. Hayre, R. R. P. Singh, T. Lin, A. G. R. Day, and M. J. P. Gingras
ArXiv 1203.4569 (2012)
Specific heat, C(T ), per mole of Yb for the model parameters in Ref. [18], in units of the Boltzmann constant
kB, calculated via NLC (up to 4th order NLC together with Euler extrapolations) are compared with experimental data
for Yb2Ti2O7. The black circles are data from Ref.

Wednesday 21 March 2012

Quantum plasmons in NPs

Plasmons go quantum

F. Javier García de Abajo
Nature 483, 417 (2012)
a, In particles larger than about 10 nanometres, plasmons emerge as collective oscillations of a gas of conduction electrons, and have a frequency that is uncertain (double-headed arrow) because of collisions among the electrons and between the electrons and the particles' atomic lattice. b, In particles smaller than 10 nm, plasmons are associated with quantum electron transitions between occupied and unoccupied energy levels. As a result, the plasmon frequency and its uncertainty, which Scholl et al. accurately measured, are larger than those for bigger particles.

Quantum plasmon resonances of individual metallic nanoparticles.
Jonathan A. Scholl, Ai Leen Koh & Jennifer A. Dionne
Nature 483, 421 (2012)
Comparison of experimental data with quantum theory. Experimental, EELS-determined localized surface plasmon resonance energies of various Ag particle diameters are overlaid on the absorption spectra generated from the analytic quantum permittivity model (a) and the DFTderived permittivity model (b). The experimental bulk resonance energies are
also included (grey dots) along with the theory prediction (grey line). Classical Mie theory peak prediction is given by the dashed white line. The experimental data begin to deviate significantly from classical predictions for particle diameters smaller than 10nm. Horizontal error bars represent 95% confidence intervals, as calculated through curve fitting and bootstrapping techniques.

Spin thermoelectric effects

Spin Caloritronics: Electron spins blow hot and cold.
Sebastian T. B. Goennenwein and Gerrit E. W. Bauer
Nature Nanotech. 7, 145 (2012)
Thermoelectrics with a spin.

Direct observation of the spin-dependent Peltier effect.
J. Flipse, F. L. Bakker, A. Slachter, F. K. Dejene and B. J. vanWees
Nature Nanotech. 7, 166 (2012)

Concept of the spin-dependent Peltier effect. a) A pure spin current is sent through a non-magnetic metal (N)/ferromagnetic metal (F) interface. In N, the Peltier heat current for both spin species is equal. As the flow direction in the two spin channels is opposite, the total heat current is cancelled. In F, the heat currents are different for majority and minority carriers, leading to a net heat current from the interface into F or vice versa. b), Generated temperature profile in the system. Spin relaxation in F reduces the spin current, thereby decreasing the induced heat current.

Microhelix magnetized coils

Magnetic Microhelix Coil Structures.
Elliot J. Smith, Denys Makarov, Samuel Sanchez, Vladimir M. Fomin, and Oliver G.Schmidt
Phys. Rev. Lett. 107, 097204 (2011)

Dynamics of radial-magnetized microhelix coils.
Vladimir M. Fomin, Elliot J. Smith, Denys Makarov, Samuel Sanchez, and Oliver G. Schmidt
Phys. Rev. B 84, 174303 (2011)
Obtainable magnetization orientations of a helix coil. Micromagnetic simulations carried out on planar and coiled-up magnetic strips: (a) Initial magnetization is inplane, perpendicular-to-strip (left); hollow-bar-magnetized helix coils can be created (right). (b) Initial magnetization is in-plane, parallel-to-strip (left), results in a corkscrew-magnetized coil (right). (c) An out-of-plane magnetized strip (left) assembles into a radial-magnetized coil (right).

Magnetodielectricity in a Manganites

Near-Room-Temperature Colossal Magnetodielectricity and Multiglass Properties in Partially Disordered La2NiMnO6.
D. Choudhury, P. Mandal, R. Mathieu, A. Hazarika, S. Rajan, A. Sundaresan, U.V. Waghmare, R. Knut,O. Karis, P. Nordblad, and D. D. Sarma
Phys. Rev. Lett. 108, 127201 (2012)

See also:
Charge Hopping in Glassy Magnets.
Gavin Lawes

Physica 5, 35 (2012)
(a) FC ZFC DC magnetization data, with an applied magnetic field (H) of 20 Oe. (b) The imaginary parts of AC susceptibility, with H =4 Oe. (c) Same as in (b), but focusing on the low-temperature region. (d) ZFC data with and without an intermediate wait (TW) at 25 K for 6000 seconds, showing distinct memory effects at TW as illustrated in the inset with a difference plot.


Role of MCD on optical magnetic recording

Role of Magnetic Circular Dichroism in All-Optical Magnetic Recording.
A. R. Khorsand, M. Savoini, A. Kirilyuk, A.V. Kimel, A. Tsukamoto, A. Itoh, and Th. Rasing
Phys. Rev. Lett. 108, 127205 (2012)
Illustration of multiple-shot switching with CP excitation pulses. In the center of the excited area, both magnetic states can switch because of the high fluence, while at the edges (i.e., between the dashed borders) helicity-dependent switching occurs and therefore a single domain state is formed. Hence, by sweeping multiple CP excitation pulses over thesurface, a large area can be switched.

Size dependence of dipolar ineractions in NPs

Size dependent dipolar interactions in iron oxide nanoparticle monolayer and multilayer Langmuir–Blodgett films.

Matthias Pauly Benoit P. Pichon Pierre Panissod Solenne Fleutot Pedro Rodriguez Marc Drillon and Sylvie Begin-Colin
J. Mater. Chem. 22, 6343 (2012)

Magnetization measurements of NP5, NP9 and NP16 dispersed in a polymer matrix: (a) hysteresis loops at 5 K, (b) ZFC/FC curves measured under a permanent field of 75 Oe and (c) imaginary part of the AC susceptibility. Inset: inverse of the
blocking temperature as a function of the measurement time (dots), and fits to the Néel–Brown law (lines).

Monday 19 March 2012

Vortices in spherical shells

Out-of-surface vortices in spherical shells.
Volodymyr P. Kravchuk, Denis D. Sheka, Robert Streubel, Denys Makarov, Oliver G. Schmidt, and Yuri Gaididei
ArXiv 1202.6002 (2012)
All possible vortex states of the spherical surface. The left column demonstrates the model out-of-surface magnetization
distribution given by Eq. (4) for all possible combinations of polarities. The right graph shows the corresponding distributions of the phase. For the correspondence, we use the notation p1p2, e.g. "+1-1" means p1 = +1 and p2 = -1

Thursday 15 March 2012

Perpendicular EB in ferrimagnet

Perpendicular exchange bias in ferrimagnetic spin valves.
F. Radu, R. Abrudan, I. Radu, D. Schmitz & H. Zabel
Nature Comms. 3, 715 (2012)

(a) Schematic view of a compensated AF interface. The interfacial energy is zero for this configuration, therefore no EB is allowed to occur. (bd) A schematic view of a compensated hard ferrimagnetic interface in contact to a ferromagnet an…

Monopoles in FMs

Monopoles in ferromagnetic metals.
Gen Tatara, Akihito Takeuchi, Noriyuki Nakabayashi, and Katsuhisa Taguchi
ArXiv 1203.2709 (2012)

GMR manipulation with multiferroics

Room Temperature Electrical Manipulation of Giant Magnetoresistance in Spin Valves Exchange-Biased with BiFeO3.
Julie Allibe, Stéphane Fusil, Karim Bouzehouane, Christophe Daumont, Daniel Sando, Eric Jacquet, Cyrille Deranlot, Manuel Bibes, and Agnès Barthélémy
Nano Lett. 12, 1141 (2012)
Magnetoelectric multiferroics are attractive materials for the development of low-power electrically controlled spintronic devices. Here we report the optimization of the exchange bias as well as the GMR effect of spin valves deposited on top of BiFeO3-based heterostructures. We show that the exchange bias can be electrically controlled through a change in the relative proportion of 109° domain walls and propose solutions toward a reversible process.

Ferroelectric memories

Inside story of ferroelectric memories.
Vincent Garcia and Manuel Bibes
483279a.pdf (application/pdf Object)

See also the previous entry: Ferroelectric solid state memories
Binary and multilevel data storage. a, In a classical binary ferroelectric random access memory (FERAM), a bit of information, with a logic value of ‘1’ or ‘0’, is encoded in the up (red block) or down (blue block) polarization direction of the device’s constituent cells. In this 36-bit example, the bits are stored in 6 × 6 cells, each of which stores one bit. Electrical wires (grey) are used to apply voltages across the cells to write and read the cells’ polarization. b, Lee et al.3 describe a multilevel FERAM that can store three bits in a single cell. In this way, three-bit logic states (000, 001, 010, 011, 100, 101, 110 and 111) can be stored in each of 3 × 4 cells of a smaller 36-bit memory array. Each state corresponds to a specific configuration of domains of opposite polarization in the cells.

Wednesday 14 March 2012

Bistability in atomic AF chains

Bistability in Atomic-Scale Antiferromagnets.
Sebastian Loth, Susanne Baumann, Christopher P. Lutz, D. M. Eigler, Andreas J. Heinrich
Science 335, 196 (2012)

Tuesday 13 March 2012

Metallic nanodumbbells

Study of Nucleation and Growth Mechanism of the Metallic Nanodumbbells.
Galyna Krylova, Lisandro J. Giovanetti, Felix G. Requejo, Nada M. Dimitrijevic, Alesia Prakapenka,and Elena V. Shevchenko
JACS 134, 4384 (2012)

Altered magnetism in maghemite NP by Cu shell

Tuning the surface magnetism of gamma-Fe2O3 nanoparticles with a Cu shell.
R. D. Desautels, E. Skoropata, Y.-Y. Chen, H. Ouyang, J. W. Freeland, and J. van Lierop
Appl. Phys. Lett. 99, 262501 (2011)

Increased surface spin stability in gamma -Fe2O3 nanoparticles with a Cu shell
R. D. Desautels, E. Skoropata, Y.-Y. Chen, H. Ouyang, J. W. Freeland, and J. van Lierop 
J. Phys. CM 24, 146001 (2012) 

Field dependence of the interfacial Cu in Cu-coated c-Fe2O3 nanoparticles.
R. D. Desautels, Y.-Y. Chen, H. Ouyang, S.-C. Lo, J. W. Freeland, and J. van Lierop

J. Appl. Phys. 111, 07B518 (2012) 
Temperature dependence of the saturation magnetization (Ms, top) and the exchange bias loop shift, Hex, of the bare gamma-Fe2O3 and Cu(0.5 nm)/Fe2O3 nanoparticles. The inset shows typical M vs mu0 H behavior of the Cu(0.5 nm)/gamma-Fe2O3 nanoparticles

Magnetization distribution in an FeO NP by SANS

Quantitative spatial magnetization distribution in iron oxide nanocubes and nanospheres by polarized small-angle neutron scattering.
S Disch1, E Wetterskog, R P Hermann, A Wiedenmann,U Vainio, G Salazar-Alvarez, L Bergström and Th Brücke
New Journal of Physics 14, 013025 (2012)
Purely nuclear SANS of spherical and cubic nanoparticles (scaled by 0.5 for display). Lines indicate fits to the model depicted in the right inset. Left inset: 10 deg sectors used for integrating the two-dimensional (2D) scattering.

Monday 12 March 2012

Reversal of individual Co islands

Magnetization Reversal of Individual Co Nanoislands.
S. Ouazi, S. Wedekind, G. Rodary, H. Oka, D. Sander, and J. Kirschner
Phys. Rev. Lett. 108, 107206 (2012)
Island size dependence of the energy barrier Delta E. (a) The blue curve is a linear fit Delta E_lin=K(N-N0)The red curve shows the calculated energy barrier for domain wall formation Delta E_dw= 4 sigma sqrt(AK).
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Fe3O4–Au NPs for biomedical applications

A Simple Approach to the Design and Functionalization of Fe3O4–Au Nanoparticles for Biomedical Applications.
A. Narsi Reddy, K. Anjaneyulu, Dr. Pratyay Basak, Dr. N. Madhusudhana Rao and Dr. Sunkara V. Manorama
ChemPlusChem ASAP (2012)
A simple aqueous synthesis of a superparamagnetic and biofunctional nanocomposite system is described. Chitosan-stabilized Fe3O4 nanoparticles were synthesized at room temperature and the surface charge of these nanocomposites was exploited to prepare nanoparticles decorated with gold.
 

Friday 9 March 2012

Tunnel current induces instability in Co NPs

Magnetic instability induced by tunnel current in single Co nanoparticles.
F. T. Birk, W. Jiang, D. Davidovic
ArXiv 1107.2850 (2012)
A: SEM of a typical sample. The scale bar indicates 0.2μm. B: Sketch representing the sample fabrication process. C-E: Current versus voltage in samples 1-3 (top to bottom), at 60mK and 0T.