Skyrmion excitations in a magnonic crystal

Collective dynamical skyrmion excitations in a magnonic crystal.

M. Mruczkiewicz, P. Gruszecki, M. Zelent, and M. Krawczyk
Phys. Rev. B 93, 174429 (2016)

Spatial maps of the x, y, and z components of the dynamic magnetization vector δm of (a) the 0.98 GHz clockwise gyrotropic mode, and (b) the 13.24 GHz breathing mode, obtained from FDTD simulations in a 30-nm nanodot under magnetic field Bz=0.1 T. Left and right columns show the absolute value and phase, respectively, of each δm component.

Magnetic properties of large Co clusters

Structural and magnetic properties of large cobalt clusters.
Jaime Souto-Casares, Masahiro Sakurai, and James R. Chelikowsky
Phys. Rev. B 93, 174418 (2016)

Local magnetic moment per atom with respect to the coordination number. Error bars represent the minimum and maximum value. Each set of points has been fitted to a line. A miniature of the specific cluster is shown, with the color map representing the individual local magnetic moment growing in the upper direction.

Rewritable artificial magnetic charge ice

Rewritable artificial magnetic charge ice.

Yong-Lei Wang, Zhi-Li Xiao,Alexey Snezhko, Jing Xu,Leonidas E. Ocola, Ralu Divan,John E. Pearson, George W. Crabtree, Wai-Kwong Kwok

Science 352, 962 (2016)

Rewritable magnetic charge ices. (A) Sketch of the experimental setup: an MFM equipped with a 2D vector magnet. The 2D solenoid magnet provides magnetic fields in any desired orientation in the sample plane. The vertically magnetized MFM probe generates a stray magnetic field (green arrows) with in-plane components at the tip. (B) Magnetization loop of a single magnetic island, with an illustration of the write, erase, and read functions. M_x, magnetization along the island. (C to G) Magnetic force microscopy images of the patterned magnetic charge ice at the same area of the sample. (C) The initial state is a type I₁ state. (D) A square area of a type III₃ state was written in the center of (C). (E) A smaller square region of type III₃ order was erased back to a type I₁ state from (D). (F) A round region of type II₂ order was written onto the freshly erased area from (E). (G) “ICE” letters of type III₄ states were scribed on a type I background state.

Multidomain Skyrmion Lattice

Multidomain Skyrmion Lattice State in Cu2OSeO3.

S. L. Zhang, A. Bauer, D. M. Burn, P. Milde, E. Neuber, L. M. Eng, H. Berger, C. Pfleiderer, G. van der Laan, and T. Hesjedal

 Nano Letters (ACS Publications)

Bubble and skyrmion crystals

Bubble and skyrmion crystals in frustrated magnets with easy-axis anisotropy.
Satoru Hayami, Shi-Zeng Lin, and Cristian D. BatistaPhys. Rev. B 93, 184413 (2016)

Schematic views of (a) a noncoplanar skyrmion texture and (b) a collinear bubble. Triangular crystals of these structures are induced by magnetic field and easy-axis anisotropy in high-symmetry frustrated magnets.

Interplay between anisotropy and EB in films

Interplay between magnetocrystalline anisotropy and exchange bias in epitaxial CoO/Co films.
Hao-Liang Liu, Steven Brems, Yu-Jia Zeng, Kristiaan Temst, André Vantomme and Chris Van Haesendonck
Journal of Physics: Condensed Matter 28, 196002 (2016)

Surface vacancy mediated pinning in maghemite NP

Surface vacancy mediated pinning of the magnetization in γ−Fe2O3 nanoparticles: A micromagnetic simulation study

Bassel Alkadour, J. I. Mercer, J. P. Whitehead, J. van Lierop, and B. W. Southern

Phys. Rev. B 93, 140411(R) (2016)

The energy landscape for a nanoparticle selected at random from the K10 enemble. Each point on the surface of the sphere represents the energy associated with the alignment of the magnetic moment. The energy is calculated using a mean field approximation based on the distribution of surface vacancies and the average angular distribution of the energy per spins at T=0 shown in Fig. 4. The energy scale associated with the color map shown on the right is given in K.

Vortex induced by impurity

Magnetic Vortex Induced by Nonmagnetic Impurity in Frustrated Magnets
Shi-Zeng Lin, Satoru Hayami, and Cristian D. Batista
Phys. Rev. Lett. 116, 187202 (2016)

Vortex solutions for $H_{\mathrm{sat}}<H<H_{\mathrm{sat}}^I$obtained from numerical simulations of $H$ in the classical limit ($S\to \infty$). (a) Vortex bound to a single-site nonmagnetic impurity for different field values. The vortex helicity is arbitrary due to the U(1) symmetry of $H$. (b) Giant vortex solution ($l=\pm 2$) obtained after removing the spins from the six sites indicated with black dots, for $J_3=-0.2777J_1$ and $Q=2\pi /12$. The saturation field is $H_{\mathrm{sat}}=0.02235\left|J_1\right|$ and $H_{\mathrm{sat}}^I=0.04725\left|J_1\right|$.

Competition between interactions and anisotropy in NPs

Understanding particle size and distance driven competition of interparticle interactions and effective single-particle anisotropy.

B Pacakova, A Mantlikova, D Niznansky, S Kubickova and J Vejpravova

Journal of Physics: Condensed Matter 28, 206004 (2016)

 Comparison of volume dependence of TMAX, representing the blocking temperature of the ensemble of the NPs with size distribution and interparticle interactions;  attributed to blocking temperature of Vm affected by interparticle interactions and finally , which is the blocking temperature attributed to Vm after decoupling the effect of dipole–dipole interactions and external DC magnetic field  mT (equation (4)). . Line corresponds to the fit encountering the finite size effect with  Jm−3,  Jm−2.

Quantum Einstein-de Haas effect

Quantum Einstein-de Haas effect.
Marc Ganzhorn, Svetlana Klyatskaya, Mario Ruben; Wolfgang Wernsdorfer
Nature Communications 7, 11443 (2016)

Particle size-dependent superspin glass behavior in random compacts of monodisperse maghemite nanoparticles - IOPscience

Particle size-dependent superspin glass behavior in random compacts of monodisperse maghemite nanoparticles.
Mikael Svante Andersson, Roland Mathieu, Peter S Normile, Su Seong Lee, Gurvinder Singh, Per Nordblad and Jose Angel De Toro
Materials Research Express 3, 045015 (2016)

 Temperature-dependent (normalized to the maximum of near the onset of dissipation) data replotted as a function of reduced temperature , where the denominator is the temperature of maximum slope of for each sample (h = 80 A m⁻¹, f = 10 Hz).

Mean-field and linear regime approach to magnetic hyperthermia of core–shell nanoparticles: can tiny nanostructures fight cancer? - Nanoscale (RSC Publishing)

Mean-field and linear regime approach to magnetic hyperthermia of core–shell nanoparticles: can tiny nanostructures fight cancer?
Marcus S. Carriao and Andris F. Bakuzis
Nanoscale 8, 8363 (2016)

The phenomenon of heat dissipation by magnetic materials interacting with an alternating magnetic field, known as magnetic hyperthermia, is an emergent and promising therapy for many diseases, mainly cancer. Here, a magnetic hyperthermia model for core–shell nanoparticles is developed. The theoretical calculation, different from previous models, highlights the importance of heterogeneity by identifying the role of surface and core spins on nanoparticle heat generation. We found that the most efficient nanoparticles should be obtained by selecting materials to reduce the surface to core damping factor ratio, increasing the interface exchange parameter and tuning the surface to core anisotropy ratio for each material combination. From our results we propose a novel heat-based hyperthermia strategy with the focus on improving the heating efficiency of small sized nanoparticles instead of larger ones. This approach might have important implications for cancer treatment and could help improving clinical efficacy.

 

Frustration in colloidal artificial ices

Engineering of frustration in colloidal artificial ices realized on microfeatured grooved lattices.
Antonio Ortiz-Ambriz, Pietro Tierno
Nature Comms. 7, 10575 (2015)

(a) Schematic view of the colloidal spin ice made by a honeycomb lattice of double-well islands filled with paramagnetic colloids. The applied field B perpendicular to the plane induces repulsive dipolar interactions between the particles. (b) Optical profilometer image of the honeycomb spin ice, and (c) the cross-section of a double well with a small central hill, giving a gravitational potential U_g. (d,e) Equilibrium state of a honeycomb ice (d) (lattice constant a=44 μm) and a square ice (e) (lattice constant a=33 μm). Blue arrows denote spin direction, while green circles highlight vertices of type K_II (in d) and S_III (in e). Scale bars, 20 μm for all images. (f,g) Vertex configurations for honeycomb (f) and square (g) ices. The lowest panel shows the normalized magnetostatic energy for each type of vertex.