Friday 25 May 2012

Interactions of SWs and DWs in a nanowire

Interaction between propagating spin waves and domain walls on a ferromagnetic nanowire.
J.-S. Kim, M. Stärk, and M. Kläui, J. Yoon and C.-Y. You, L. Lopez-Diaz and E. Martinez
Phys. Rev. B 85, 174428 (2012)
(a) The SW amplitudes as a function of time (t = 5.0–5.5 ns with fH = 6.0 GHz, B0 = 200 mT, and Bext = 0.5 mT) at the TW position (x = 500 nm and x = 700 nm) (black line, the SW amplitude without a TW; red line, the SW amplitude with a TW). (b) The FFT spectra of the SW amplitude for the case of (a) at the TW position (x = 500 nm). (c) The SW amplitudes as a function of time at x = 500 nm (t = 5.0–10.0 ns with fH = 11.0 GHz, B0 = 200 mT, and Bext = 0.8 mT). (d) The FFT spectrum of the SW amplitude for the case of  (c) at the TW position. Inset shows the snapshots of the y-component magnetization for two different simulation times.

Singl adatoms with thermal stability

Ordered Array of Single Adatoms with Remarkable Thermal Stability: Au/Fe3O4(001)
Zbynek Novotny, Giacomo Argentero, Zhiming Wang, Michael Schmid, Ulrike Diebold, and Gareth S. Parkinson
Phys. Rev. Lett. 108, 216103 (2012)

Magnon decays: a review

Spontaneous Magnon Decays.
M. E. Zhitomirsky, A. L. Chernyshev
ArXiv 1205.5278 (2012)
Zero-temperature self-energy diagrams due to the three-magnon, (a) and (b), and four-magnon, (c) and (d), interactions.

Complex interacting DW in FM

Domain-wall complexes in ferromagnetic stripes.
Andrzej Janutka
Phys. Rev. B 85, 184421 (2012)

DW configurations; a) a transverse DW, b) a vortex DW. In the upper draws, arrows indicate magnetization alignment.

Thursday 24 May 2012

Control of DW by electric fields

 Electric-field control of domain wall motion in perpendicularly magnetized materials.
A.J. Schellekens, A. van den Brink, J.H. Franken, H.J.M. Swagten & B. Koopmans
Nature Communications 3, 847 (2012)
Schematic overview of methods to control DW motion. In (a) and (b), the experimentally well-established field- and current-induced DW motion are depicted. In (c), the here-proposed mechanism is shown, namely DW manipulation by an electric field. (d) Overview of the lateral structure of the sample to study DW motion under influence of an electric field.

Tuesday 22 May 2012

Molecular Nanomagnets and Magnetic Nanoparticles: A Review

Exploring the No-Man s Land between Molecular Nanomagnets and Magnetic Nanoparticles.
Dante Gatteschi, Maria Fittipaldi, Claudio Sangregorio, and Lorenzo Sorace

Angew. Chem. Int. Ed. 51, 4792 (2012)
That's about the size of it: A comparison of structural and magnetic properties of iron oxo based molecular nanomagnets (see picture, right) and magnetic nanoparticles (left) gives a deeper understanding of the magnetic behavior at the intermediate scale between molecular and bulk objects.

Nanocube supercrystals

Colloidal Nanocube Supercrystals Stabilized by Multipolar Coulombic Coupling.
Henry Chan, Arnaud Demortière, Lela Vukovic, Petr Kral and Christophe Petit
ACS Nano 6, 4203 (2012)
We explore microscopic principles governing the self-assembly of colloidal octylamine-coated platinum nanocubes solvated in toluene. Our experiments show that regular nanocubes with an edge length of lRC = 5.5 nm form supercrystals with simple cubic packing, while slightly truncated nanocubes with an edge length of lTC = 4.7 nm tend to arrange in fcc packing. We model by averaged force fields and atomistic molecular dynamics simulations the coupling forces between these nanocrystals. Our detailed analysis shows that the fcc packing, which for cubes has a lower density than simple cubic packing, is favored by the truncated nanocubes due to their Coulombic coupling by multipolar electrostatic fields, formed during charge transfer between the octylamine ligands and the Pt cores.

Logic operations using vortex networks

Logic Operations Based on Magnetic-Vortex-State Networks.
Hyunsung Jung, Youn-Seok Choi, Ki-Suk Lee, Dong-Soo Han, Young-Sang Yu, Mi-Young Im,
Peter Fischer, and Sang-Koog Kim

Nano Letters 6, 3712 (2012)
Experimental setup for the direct demonstration of XOR logic operation using the indicated vortex-state network
and full-field soft X-ray microscopy. Schematic layout of soft X-ray measurement setup for direct readout of output signals in disk 2, showing the sample (chain of three vortex-state Py disks) with electrodes on both end disks for application of input signals. Equal diameter 2R = 2.4 μm, thickness L = 50 nm, and center-to-center distance dint = 2.46 μm are used for the experimental sample. The right inset shows the initial ground vortex states measured by the microscope through XMCD
contrast (the same as those shown in Figure 1). Sinusoidal oscillating magnetic fields of 4.5 Oe amplitude and 160 MHz
frequency are applied to disk 1 and/or disk 3.

DW in a Co nanocontact

Theoretical study of magnetic domain walls through a cobalt nanocontact.
Laszlo Balogh, Krisztian Palotas, Laszlo Udvardi, Laszlo Szunyogh, and Ulrich Nowak
Phys. Rev. B 86, 024406 (2012)
(a) The geometry of the contact viewed from the (110) direction. The leads are depicted as dark (blue) rectangles, the cobalt atoms forming the contact are represented by gray (orange) circles, and a denotes the nearest neighbor distance in
the fcc structure. (b) Sketch of the embedded cluster. Dark (blue) circles: selected atoms of the cobalt leads; gray (orange) circles: cobalt atoms in the nanocontact; empty circles: empty spheres around the contact.

NPs for Detection and Treatment of Cancer

Hybrid Nanoparticles for Detection and Treatment of Cancer.
Michael J. Sailor and Ji-Ho Park
Adv. Mater. 24, 3779 (2012)

SW and DW interactions in a nanowire

Interaction between propagating spin waves and domain walls on a ferromagnetic nanowire
J.-S. Kim, M. Stärk, and M. Kläui, J. Yoon and C.-Y. You, L. Lopez-Diaz and E. Martinez
Phys. Rev. B 85, 174428 (2012)
The initial spin configuration of the trapped head-to-head TW nucleated at the position of a square notch in the center of the nanowire. The square notch size is 5 × 5 nm2. In the bottom we zoom into the central part of the wire to show the internal structure of the TW pinned at the notch. In order to generate SWs, we apply a localized sinusoidal field at a position denoted as the SW source. The SW source is located at 500 nm from the center of the nanowire. To depin the TW, we apply an external field Bext along the ±x direction.

Friday 18 May 2012

Dynamics of SP NPs by NMR

1H-NMR study of the spin dynamics of fine superparamagnetic nanoparticles.
L. Bordonali,Y. Furukawa, M. Kraken, F. J. Litterst, C. Sangregorio, M. F. Casula, and A. Lascialfari
Phys. Rev. B 85, 174426 (2012)
Average proton spin-lattice relaxation rate  plotted vs temperature for two external magnetic fields. Inset: semilog plot of the distributions of energy barriers related to the two investigated static fields, as extracted from Eq. (2).

Wednesday 16 May 2012

Phase diagram of dilute dipolar Ising system

Experimental phase diagram and dynamics of a dilute dipolar-coupled Ising system.
J. A. Quilliam, S. Meng, and J. B. Kycia
Phys. Rev. B 85, 184415 (2012)
Current understanding of the phase diagram of LiHoxY1−xF4 as a function of concentration x and temperature T .

Phase diagram for vortex dynamics

Phase diagram of magnetic vortex dynamics.
T. Y. Chen, A. T. Galkiewicz, and P. A. Crowell
Phys. Rev. B 85, 180406 (2012)
Gyrotropic response as a function of excitation amplitude and frequency for (a) experiment and (b) numerical calculations. The experimental parameter space is above the horizontal dashed line in (b). The color scale is logarithmic. The contours are shown for increasing amplitude. The dashed curve in (b) shows the lower boundary of the region in which two gyrotropic
orbits exist.

Generating skyrmions by injection of spin current

Skyrmion generation by current.
Youngbin Tchoe and Jung Hoon Han
Phys. Rev. B 85, 174416 (2012)
Skyrmion generation by circulating spin current source in the FM background. (a) Time dependence of the total  Skyrmion number Q(t ). Q(0) ≈ −2 is nonzero from the residual anti-Skyrmions in the ferromagnetic background. Blue (red) colored curves correspond to CW (CCW) circulating current with the j0 value indicated for each curve. (b)–(l) Time-dependent snapshots of the spin configuration over the green-circled time interval in (a).

Structuration and Integration of Magnetic Nanoparticles on Surfaces and Devices - Bellido - 2012 - Small - Wiley Online Library

Structuration and Integration of Magnetic Nanoparticles on Surfaces and Devices.
Elena Bellido , Neus Domingo , Isaac Ojea-Jiménez , and Daniel Ruiz-Molina
Small 8, 1465 (2012)
A detailed review of the experimental approaches followed for the structuration of magnetic nanoparticles on surfaces is presented. Special attention is given to understand the parameters that control self-assembly, including the use of biological templates. Finally, the implementation of all the knowledge previously gained is translated to the integration and implementation on sensors and devices.

Monday 14 May 2012

EB in magnetoelectrics

Exchange biasing of magnetoelectric composites.
Enno Lage, Christine Kirchhof, Viktor Hrkac, Lorenz Kienle, Robert Jahns, Reinhard Knöchel,
Eckhard Quandt and Dirk Meyners

Nature Mater. AOP (2012)
Antagonism bw. EB and magnetostriction: Normalized magnetization curves (black) and magnetostriction curves (red) of Fe50Co50 multilayers deposited on cantilevers. a,b, The pinning direction is induced either parallel (a) or perpendicular (b) to the longitudinal cantilever axis. Whereas the exchange bias shows a maximum value when measured parallel to the pinning direction, the magnetostrictive response almost vanishes. In the case of the measurement perpendicular to the pinning direction, the projection of the exchange bias vanishes; however, the magnetostrictive response is maximal.

DW heat conductance

Domain wall heat conductance in ferromagnetic wires.
Peng Yan and Gerrit E.W. Bauer
ArXiv 1204.4008. (2012)
(a) The magnetization profile of a wide head-to-head DW (solid line). The numerical SW solution (circles) for frequency ! in a linear ferromagnetic chain cannot be distinguished from the solution (dashed line) for the continuum model. (b) A computed narrow DW profile (triangles) compared with the Walker model (squares). The SW amplitude for a selected frequency is shown by circles. (c) The ground state profile of an abrupt DW (triangles) compared with the Walker profile (squares). The amplitude of a SW for another given frequency is shown by circles.

Friday 11 May 2012

Restoration of bulk magnetism in Fe oxide NPs by surfactant molecules

Surfactant Organic Molecules Restore Magnetism in Metal-Oxide Nanoparticle Surfaces.
Juan Salafranca, Jaume Gazquez, Nicolás Pérez, Amílcar Labarta, Sokrates T. Pantelides, Stephen J. Pennycook, Xavier Batlle, and Maria Varela
Nano Lett., 12, 2499 (2012)
Left: Density of states (DOS) projected over the majority spin d orbitals in the octahedral iron sites within different crystal environments. Organic acid bonded to magnetite surface. DOS projected over octahedral iron bonded to the organic acid. Because of the influence of the oxygen ions in the carboxylic group, occupancies are very similar to the bulk case, and the reduction of magnetization at the surface is partially lifted. Middle:  High-resolution Z-contrast STEM images of a Fe3O4 NP showing high crystal quality. Right: Top: L2,3 profile along the direction of the blue arrow in panel d (in red and in black for I+ and I− L23 ratio maps respectively). Bottom: difference between I+ and I− L2,3 ratios along the NP. The scale bar represents 5 nm in all panels.   


Spin ice on a triangular lattice

Extending spin ice concepts to another geometry: The artificial triangular spin ice.
L. A. S. Mól, A. R. Pereira, and W. A. Moura-Melo
Phys. Rev. B 85, 184410 (2012)
The 64 possible vertices, grouped by increasing energy (left to right) in 8 topologies. Vertices type 1, 3, and 5 satisfy the three-in/three-out ice rule, while vertices type 2, 4, and 6 are single magnetic charges. Vertices type 7 and 8 are double and triple charged vertices, respectively.

Wednesday 9 May 2012

Ultrafast magnetization dynamics by electrons and phonons

Electron- and phonon-mediated ultrafast magnetization dynamics of Gd(0001)
Muhammad Sultan, Unai Atxitia, Alexey Melnikov, Oksana Chubykalo-Fesenko, and Uwe Bovensiepen
Phys. Rev. B 85, 184407 (2012)
Schematic diagram of the model. The multispin LLB model (center) is coupled to the 2T model via two
coupling mechanisms: phonon contribution via Raman processes (left) and electron contribution via dynamical spin polarization of carriers which produces a change of chemical potential μ (Ref. 37) (right). The 2T model and the LLB model are time and layer resolved and the electron diffusion is considered. The change in the phonon population with temperature is taken into account within the Debye model. The parameters of the 2T model were taken from Refs. 27
and 29.

Tuesday 8 May 2012

Exchange bias and training effects in manganite NPs

Some articles devoted to finite-size and exchaneg bias effects in manganite NPs:

Oscillatory exchange bias and training effects in nanocrystalline Pr0.5Ca0.5MnO3.
S. Narayana Jammalamadaka, S. S. Rao, S. V. Bhat, J. Vanacken, and V. V. Moshchalkov
AIP Advances 2, 012169 (2012)
(a) T variation of oscillatory exchange bias field (OEB) (b) Variation of M with FC (c) M-H loops resulted from
one step and two step field cooling process. Symmetric MH loops are evident after two step process (d) HEB and HC variation with FC. The red curve is the fit obtained from equation (1), scattered points are the experimental data.

Probing the existing magnetic phases in Pr0.5Ca0.5MnO3 (PCMO) nanowires and nanoparticles: magnetization and magneto-transport investigations.
S S Rao and S V Bhat
J. Phys. Condens. Matter 22, 116004 (2010) 
After cooling PCMO 20 in 2, 6 and 8 T, the field is isothermally changed to 4 T at 5 K and the magnetization is measured while warming (FA 2 T, FA 6 T, FA 8 T). The variation of magnetization with the temperature in zero-field cooling (4 and 6 T), field-cooled cooling and warming at 4 T is shown as ZFC 4 T, ZFC 6 T and FCCW 4 T (a). A similar protocol was followed as mentioned above in the case of PCMO 40 to measure the magnetization with temperature (b).

Surface spin glass and exchange bias effect in Sm0.5Ca0.5MnO3 manganites nano particles
S. K. Giri, A. Poddar, and T. K. Nath

AIP Advances 1, 032110 (2011)
The schematic representation of the phenomenological model for CO/AFM bulk manganites and the corresponding nanograins.

Toroidocaloric effect

Thermodynamics of ferrotoroidic materials: Toroidocaloric effect
Teresa Castán and Antoni Planes, Avadh Saxena
e144429 (application/pdf Object)
Toroidocaloric effect as a function of temperature and selected values of the applied toroidal field, κ = 0.90,1.0, and 1.05.

Monday 7 May 2012

Spin torque

Spin-Torque Switching with the Giant Spin Hall Effect of Tantalum.
Luqiao Liu, Chi-Feng Pai, Y. Li, H. W. Tseng, D. C. Ralph, R. A. Buhrman
Science 336, 555 (2012)
ST-FMR induced by the spin Hall effect at room temperature. (A) Sample geometry for the ST-FMR measurement. IRF and HRF represent the applied radio frequency current and the corresponding Oersted field. Tau_h is the torque on the magnetization due to the Oersted field, and Tau_ST is the spin-transfer torque from the spin Hall effect. Resonant line shapes of the STFMR signals under a driving frequency f = 9 GHz for (B) CoFeB(4 nm)/Ta(8 nm) and (C) CoFeB(3 nm)/Pt
(6 nm). The squares represent experimental data, whereas the red curves are fits to a sum of symmetric and antisymmetric Lorentzians. From the ratio of the symmetric and antisymmeteric peak components in (C), we determine the JS/Je ratio for Pt to be ~0.07, consistent with earlier work (19). Vmix is the measured dc voltage due to the mixing of oscillating resistance and radio frequency current. The inset to (B) shows the dependence of the frequency f on the resonance magnetic field, in agreement with the Kittel formula (solid curve). (D) The resonance linewidth as determined from ST-FMR signals such as
those shown in (B) and (C) at different resonance frequencies. The Gilbert damping coefficients a for Ta and Pt are calculated from the linear fits to these linewidth data. CFB, CoFeB.

Electronic order and frustration

The Impact of Ionic Frustration on Electronic Order
Leon Balents
Science 336, 547 (2012)
Frustrated ordering. Artist’s conception of a nanoscale region of honeycomb lattice of ionic and spin structure in Ba3CuSb2O9 studied by Nakatsuji et al. Copper-antimony (Cu-Sb) dumbbells are oriented vertically, with Cu atoms in red and Sb in blue.


Spin-Orbital Short-Range Order on a Honeycomb-Based Lattice.
S. Nakatsuji, et al.
Science 336, 559 (2012)
(A) Centrosymmetric P63/mmc high-T structure of Ba3CuSb2O9 indicating nanoscale Cu-Sb dumbbell ordering. (B) A characteristic vertex with spin-orbital degrees of freedom for the Cu-honeycomb lattice of Ba3CuSb2O9. A trigonal coverage of a Cu-hexagon by spin singlets (pair of blue or green arrows) based on a dx2−y2 ferro-orbital (green) state at two Cu sites (blue shaded) is shown.  (C) Superstructure peaks found in an (h k 10) slice extracted from a 3D volume of synchrotron x-ray diffraction data at 20 K for an orthorhombic single-crystalline sample (12).

Thursday 3 May 2012

Dynamics of coupled domain walls

Dynamic Oscillations of Coupled DomainWalls.
L. O’Brien, E. R. Lewis, A. Ferna´ndez-Pacheco, D. Petit, and R. P. Cowburn, J. Sampaio and D. E. Read
Phys. Rev. Lett. 108, 187202 (2012)
(a) Micromagnetic simulation of two magnetostatically coupled HH and TT DWs in parallel nanowires. (b) DW-DW interaction coupling strength K as a function of width w and wire separation d. (c) Parameters of the DW 1D model: uniform cant angle and central position x. (d) Resonant frequency of DW-DW interaction as a function of separation, d, and thickness t (w ¼ 50 nm). (e) Q factor of resonance as a function of d and t (w ¼ 50 nm).

DW dynamics on a topological insulator

Thin-Film Magnetization Dynamics on the Surface of a Topological Insulator.
Yaroslav Tserkovnyak and Daniel Loss
Phys. Rev. Lett. 108, 187201 (2012)
Schematic of a DW in a ferromagnetic strip with an out-of-plane easy (z) axis anisotropy, deposited on the surface of a TI. The DW (of width dw) is parametrized, according to Eq. (2), by two soft dynamic coordinates: its position xdwðtÞ and azimuthal angle dwðtÞ. At the DW position, xdw, the magnetization m lies fully in the xy plane (forming angle dw with the x axis). A chiral electron mode (of width dw) formed in the TI under the DW carries transport current Idw at its exit point, which is governed by the voltage Vy applied to the TI surface at its entrance and the fictitious electromotive force generated by the DW dynamics along its length. An Onsager-reciprocal spin torque affects DW dynamics in the presence of Idw.

Realization of transverse-field Ising ferromagnet in molecular cluster

Transverse field Ising ferromagnetism in Mn12-acetate-MeOH.
P. Subedi, A. D. Kent, Bo Wen, M. P. Sarachik, Y. Yeshurun, A. J. Millis, S. Mukherjee, and G. Christou
Phys. Rev. B 85, 134441 (2012)
The change in inverse susceptibility normalized to the susceptibility at zero field versus H2⊥ for Mn12-ac-
MeOH (green dots, open circle Ref. 21) and Mn12-ac (red squares, half filled, and solid squares are sample A and B in Ref. 16) at T = 3.2 K. The red dashed line is calculated using the random-field model of Ref. 16 (RFIFM) for the root-mean-square tilt angle of 1.8◦. The solid green line shows the result for the case with no tilt angle (TFIFM).

Control of DW pining in a nanowire system

Field-controlled domain wall pinning-depinning effects in a ferromagnetic nanowire-nanoislands system.
V. L. Mironov, O. L. Ermolaeva, E. V. Skorohodov, and A. Yu. Klimov
Phys. Rev. B 85, 144418 (2012)
(a) The A-type configuration of magnetization in the NW-NI system in an external magnetic field. (b) The potential energy profiles ENW (xDW) for different external magnetic fields. The solid line 1 is the energy profile at zero field. The solid line 2 is for the critical external field HB = 47 mT. The dashed line 3 is for the intermediate field 0.5HB. The DW pinning position is indicated schematically by the circle on curve 3. The energy landscape calculated directly from OOMMF simulations taking into account the effects of DW and NI magnetization disturbance is indicated by circles. (c) The model magnetization distribution in the NW-NI system at Hex = Hnuc, demonstrating the DW pinning on the potential barrier before the NIs. The S state in the NIs’ magnetization was caused by the external magnetic field. (d) The model MFM
contrast distribution from the NW-NI system (without nucleating pad) corresponding to the magnetization distribution shown in (c). The white arrow in the MFM image indicates the bright pole, which corresponds to a transverse DW.

Wednesday 2 May 2012

Control of magnetism atom by atom

Atom-by-atom engineering and magnetometry of tailored nanomagnets.
Alexander Ako Khajetoorians, JensWiebe, Bruno Chilian, Samir Lounis, Stefan Blügel and RolandWiesendanger
Nature Physics AOL (2012)
Antiferromagnetic chains of even and odd numbers of Fe atoms. Top panels: magnetization states from pair-KKR Ising model (left, partly degenerate) and magnetic images (right) of chains of antiferromagnetically coupled Fe atoms on Cu(111) with a lengths of three (a) to seven (e) atom

Universality of spin-phonon splitting in AF

Universal Exchange-Driven Phonon Splitting in Antiferromagnets.
Ch. Kant, M. Schmidt, Zhe Wang, F. Mayr, V. Tsurkan, J. Deisenhofer, and A. Loidl
Phys. Rev. Lett. 108, 177203 (2012)
Magnetic properties of the investigated TMMOs. (a) Magnetic unit cell showing the AF order along [111]. (b) Splitting into phonon modes with eigenfrequencies omega perp and omega par. (c) Nearest-neighbor coupling J1 and dominant next-nearest neighbor coupling J2. (d) Neel temperatures vs J2S(S+1) using values for J2 taken from Ref. [26] in comparison to the mean-field expectation (dashed line).

Control of ferroelectics magnetization by E field

Electric Field Control of Nonvolatile Four-State Magnetization at Room Temperature.
Sae Hwan Chun, Yi Sheng Chai, Byung-Gu Jeon, Hyung Joon Kim, Yoon Seok Oh, Ingyu Kim, Hanbit Kim, Byeong Jo Jeon, So Young Haam, Ju-Young Park, Suk Ho Lee, Jae-Ho Chung, Jae-Hoon Park, and Kee Hoon Kim
Phys. Rev. Lett. 108, 177201 (2012)
The MðEÞ curves at zero H bias obtained after applying four different ME poling (states 0, 1, 2, and 3) as
indicated in the inset.