Tuning shape, exchange and surface anisotropy of core/shell NPs

Nanoscale Magnetism Control via Surface and Exchange Anisotropy for Optimized Ferrimagnetic Hysteresis.
Seung-hyun Noh, Wonjun Na, Jung-tak Jang, Jae-Hyun Lee, Eun Jung Lee, Seung Ho Moon,
Yongjun Lim, Jeon-Soo Shin, and Jinwoo Cheon
Nano Letters 12, 3716 (2012)

Morphological and structural evolution of magnetic nanoparticle and correlated tunability of nanomagnetism. (a) Magnetic NPs with various structural motifs exhibiting differences in size, surface anisotropy, and exchange anisotropy. (b) Magnetism tuning by the systematicchanges of magnetic nanoparticles. Graphs i−iv correspond to the nanoparticles shown in part a where modulation of structural motifs is needed to control parameters such as K, Hc, Ms, or Mr.

Images and magnetization behaviors of cube and sphere nanoparticles. (a) TEM images of cube (18 nm (σ ≈ 5%) in edge length) and (b) sphere nanoparticle (22 nm (σ ≈ 7%) in diameter). Nanoparticles have identical composition (Zn_0.4Fe_2.6O₄) and magnetic volume (5.8 × 10^–24 m³). (c) High resolution TEM image of cube exhibiting well-defined lattice fringes of {100} faces. (d) M-H curves of cube and sphere measured at 300 K using SQUID. M_s of cube is 165 emu/g_(Fe+Zn), and that of sphere is 145 emu/g_(Fe+Zn). Simulated magnetic spin states of (e) cube and (f) sphere by using OOMMF program. The color map indicates the degree of spin canting against external magnetic field (B₀) where red indicates nondeviated spins and blue indicates highly canted spins. Local spin states on the surfaces of nanoparticles are depicted on the right corners of parts e and f. Cube exhibits lower spin disorder rate of 4% than sphere of 8%.

Core/shell NPs for MRI and Tomography

Multifunctional Fe3O4/TaOx Core/Shell Nanoparticles for Simultaneous Magnetic Resonance Imaging and X-ray Computed Tomography.
Nohyun Lee, Hye Rim Cho, Myoung Hwan Oh, Soo Hong Lee, Kangmin Kim, Byung Hyo Kim, Kwangsoo Shin, Tae-Young Ahn, Jin Woo Choi, Young-Woon Kim, Seung Hong Choi, and Taeghwan Hyeon

JACS 134, 10309 (2012)

Schematic Illustration of Synthesis and Modification of Fe3O4/TaOx Core/Shell NPs

Magnetic and plasmonic Au/Fe oxide composite NPs: compilation

1) Exchange bias effect in Au-Fe3O4 nanocomposites.
Sayan Chandra, N A Frey Huls, M H Phan, S Srinath, M A Garcia, Youngmin Lee, Chao Wang, Shouheng Sun, Òscar Iglesias and H Srikanth

Nanotechnology 25, 055702 (2014)

Low temperature hysteresis loops simulated after a cooling in a magnetic field h_FC = 100 K as computed by MC simulations of individual nanoparticles with cluster (a) and dimer (b) geometries. The non-magnetic metal is simulated as a hole in the middle for the cluster geometry and a sharp facet for the cluster. Panels (a) and (b) show hysteresis loops of a particle with cluster and dimer geometry, respectively, for two different values of the surface anisotropy constant: k_S = 0.01 (blue squares) equal to the core value k_C = 0.01, and increased surface anisotropy k_S = 30 (red circles). The dashed lines in (b) stand for a spherical particle of the same size as the dimer. The inset displays the contribution of the surface (yellow circles) and core (green squares) spins of a dimer particle to the hysteresis loop for k_s = 30. Snapshots of the spin configurations for cluster ((c) and (d) panels) and dimer ((e) and (f) panels) particles for k_S = 30 obtained at the end of the FC process ((c) and (e) panels) and at the coercive field point of the decreasing field branch ((d) and (f) panels) of the hysteresis loops displayed in figures (a) and (b). For clarity, only a slice of width 4a along the applied field direction and through the central plane of the particles is shown. Surface spins have darker colors and core spins have been colored lighter.

2) Chemically synthesized Au–Fe3O4 nanostructures with controlled optical and magnetic properties. Victor Velasco, Laura Muñoz, Eva Mazarío, Nieves Menéndez, Pilar Herrasti, Antonio Hernando and Patricia Crespo

J. Phys. D: Appl. Phys. 48, 035502 (2015)

(a) ZFC-FC magnetization curves of Fe₃O₄ and Au–Fe₃O₄ NPs measured under an applied field of 25 Oe. (b) Hysteresis loops of Fe₃O₄ and Au–Fe₃O₄ NPs with Au : Fe initial molar ratios of 1 : 1 and 1 : 3 measured at 5 K applying a maximum field of 50.000 Oe. The ferromagnetic behaviour is highlighted in the inset.

3) Spin Dynamics in Hybrid Iron Oxide-Gold Nanostructures.

Tomas Orlando,A. Capozzi, E. Umut, L. Bordonali, M. Mariani, P. Galinetto, F. Pineider, C. Innocenti,  P. Masala,  F. Tabak,  M. Scavini, P. Santini, M. Corti, C . Sangregorio, P. Ghigna, and A. Lascialfari

Journal of Physical Chemistry C 119, 1224 (2015) 

 

We report a broadband ¹H NMR study of the spin dynamics of coated maghemite and gold–maghemite hybrid nanostructures with two different geometries, namely dimers and core–shells. All the samples have a superparamagnetic behavior, displaying a blocking temperature (T_B ∼ 80 K (maghemite), ∼105 K (dimer), ∼150 K (core–shell)), and the magnetization reversal time follows the Vogel–Fulcher law. We observed three different anomalies in ¹H NMR T₁^–1 versus T that decrease in amplitude when increasing the applied magnetic field. We suggest that the anomalies are related to three distinct system dynamics: molecular rotations of the organic groups (240 < T < 270 K), superparamagnetic spin blockage (100 < T < 150 K), and surface–core spin dynamics (T < 25 K). By fitting the T₁^–1 data with a heuristic model, we achieved a good agreement with magnetic relaxation data and literature values for methyl group rotation frequencies.

 

4) Superparamagnetic Au-Fe3O4 nanoparticles: one-pot synthesis, biofunctionalization and toxicity evaluation.

A Pariti, P Desai, S K Y Maddirala, N Ercal, K V Katti, X Liang and M Nath

Materials Research Express 1, 035023 (2014)
5) Spin-Polarization Transfer in Colloidal Magnetic-Plasmonic Au/Iron Oxide Hetero-nanocrystals.
Francesco Pineider, César de Julián Fernández, Valeria Videtta, Elvio Carlino, Awni al Hourani,Fabrice Wilhelm, Andrei Rogalev, P. Davide Cozzoli, Paolo Ghigna, and Claudio Sangregorio

ACS Nano 7, 857 (2013)

We report on the unprecedented direct observation of spin-polarization transfer across colloidal magneto-plasmonic Au@Fe-oxide core@shell nanocrystal heterostructures. A magnetic moment is induced into the Au domain when the magnetic shell contains a reduced Fe-oxide phase in direct contact with the noble metal. An increased hole density in the Au states suggested occurrence of a charge-transfer process concomitant to the magnetization transfer. The angular to spin magnetic moment ratio, m_orb/m_spin, for the Au 5d states, which was found to be equal to 0.38, appeared to be unusually large when compared to previous findings. A mechanism relying on direct hybridization between the Au and Fe states at the core/shell interface is proposed to account for the observed transfer of the magnetic moment.

Surface and EB effects in core/shell and hollow NPs: compiliation

Impacts of surface spins and inter-particle interactions on the magnetism of hollow γ-Fe₂O₃ nanoparticles.

Hafsa Khurshid, Zohreh Nemati Porshokouh, Manh-Huong Phan, Pritish Mukherjee, and Hariharan Srikanth

J. Appl. Phys. 115, 17E131 (2014)

Temperature dependence of ZFC and FC magnetization taken in a field of 50 Oe for (a) 10 nm and (b) 15 nm hollow particles.

Tuning exchange bias in Fe/γ-Fe₂O₃ core-shell nanoparticles: Impacts of interface and surface spins.

Hafsa Khurshid, Manh-Huong Phan, Pritish Mukherjee, and Hariharan Srikanth

Appl. Phys. Lett. 104, 072407 (2014) 

Temperature dependence of the net moment of frozen spins ( M f ) for (a) 15 nm, (b) 10 nm, and (c) 8 nm Fe/γ-Fe 2O 3 nanoparticles. H EB and M f are plotted as a function of particle size (d).

Mechanism and controlled growth of shape and size variant core/shell FeO/Fe3O4 nanoparticles.
Hafsa Khurshid, Wanfeng Li, Sayan Chandra, Manh-Huong Phan, George C. Hadjipanayis, Pritish Mukherjee and Hariharan Srikanth

Nanoscale 5, 7942 (2013) 

Hysteresis loops (M–H) measured in the ZFC and FC protocols for cubic, spherical, and octopod-shaped FeO/Fe₃O₄ nanoparticles. The inset of (a) shows an enlarged portion of the M–H curves featuring the low-field jump in the FC magnetization of the cubic nanoparticles. This feature is less pronounced in the case of the octopod-shaped nanoparticles (c) and is almost absent in the case of the spherical nanoparticles (b).

Asymmetric hysteresis loops and its dependence on magnetic anisotropy in exchange biased Co/CoO core-shell nanoparticles.

Sayan Chandra, Hafsa Khurshid, Manh-Huong Phan and Hariharan Srikanth

Appl. Phys. Lett. 101, 232405 (2012)

(a) Temperature dependence of exchange bias field for cooling field of 1 T and (b) temperature dependence of isothermal remanence. Insets in (a) show the ZFC and FC hysteresis loops at 10 K and 100 K. Inset in (b)shows the temperature dependence of blocking function distribution.

Surface spin disorder and exchange-bias in hollow maghemite nanoparticles.

Hafsa Khurshid, Wanfeng Li, Manh-Huong Phan, Pritish Mukherjee, George C. Hadjipanayis and Hariharan Srikanth

Appl. Phys. Lett. 101, 022403 (2012)

The FC M( H) loops taken at 5 K for (a) 9.2 nm and (b) 18.7 nm hollow nanoparticles. The TEM image of the 18.5 nm solid nanoparticles is shown in the inset of (b).

DWs in magnetic nanotubes

Chiral symmetry breaking and pair-creation mediated Walker breakdown in magnetic nanotubes.
Ming Yan, Christian Andreas, Attila Kákay, Felipe García-Sánchez and Riccardo Hertel Appl. Phys. Lett. 100, 252401 (2012)

(a) Simulated configuration of a vortex-like DW formed in a magnetic nanotube and the definition of its chirality by combining vorticity and field direction. (b) The unrolled tube with the DW. The red line is the plot of the radial component averaged over each cross-section. (c) For comparison, a transverse DW in a flat strip.

Simulations of large arrays of Core/Shell NP

Mesoscopic Model for the Simulation of Large Arrays of Bi-Magnetic Core/Shell Nanoparticles.
G. Margaris, K. N. Trohidou, and J. Nogués
Advanced Materials 24, 4331 (2012)

A mesoscopic approach to simulate large arrays of core/shell nanoparticles based on the reduction of the number of simulated spins is presented. The model is used to simulate arrays of Co/CoO nanoparticles with different nanoparticle densities.

Spin ice with perpendicular anisotropy

Perpendicular Magnetization and Generic Realization of the Ising Model in Artificial Spin Ice.
Sheng Zhang, Jie Li, Ian Gilbert, Jason Bartell, Michael J. Erickson, Yu Pan, Paul E. Lammert, Cristiano Nisoli, K. K. Kohli, Rajiv Misra, Vincent H. Crespi, Nitin Samarth, C. Leighton, and Peter Schiffer Phys. Rev. Lett. 109, 087201 (2012)

SEM and MFM images of perpendicular moment nanomagnet arrays in kagome and honeycomb geometries with 600 nm lattice spacing. Each island in MFM shows either black or white, indicating that it consists of a single magnetic domain with moment pointing either up or down.

Spin-phonon coupling signature of SP in NPs

Spectroscopic Signature of the Superparamagnetic Transition and Surface Spin Disorder in CoFe2O4 Nanoparticles.
Qi -C. Sun, Christina S. Birkel, Jinbo Cao, Wolfgang Tremel, and Janice L. Musfeldt
ACS Nano 6, 4876 (2012)

Phonons are exquisitely sensitive to finite length scale effects in a wide variety of materials. To investigate confinement in combination with strong magnetoelastic interactions, we measured the infrared vibrational properties of CoFe₂O₄ nanoparticles and compared our results to trends in the coercivity over the same size range and to the response of the bulk material. Remarkably, the spectroscopic response is sensitive to the size-induced crossover to the superparamagnetic state, which occurs between 7 and 10 nm. A spin–phonon coupling analysis supports the core–shell model. Moreover, it provides an estimate of the magnetically disordered shell thickness, which increases from 0.4 nm in the 14 nm particles to 0.8 nm in the 5 nm particles, demonstrating that the associated local lattice distortions take place on the length scale of the unit cell. These findings are important for understanding finite length scale effects in this and other magnetic oxides where magnetoelastic interactions are important.

Spin precession in spin current

Towards coherent spin precession in pure-spin current.
Hiroshi Idzuchi, Yasuhiro Fukuma & YoshiChika Otani
Scientific Reports 2, 628 (2012)

(a) Schematic diagram of lateral spin valve with dual injectors in non-local measurement configuration. (b) Schematic diagram of LSV with single injector and the spatial variation of spin accumulation δμ for Ag.  (c), (d) Schematic diagram of LSV with dual injectors with parallel or anti-parallel configuration and the spatial variation of spin accumulation δμ for Ag.

Elctric dipoles in spin ice

Electric dipoles on magnetic monopoles in spin ice.
D.I. Khomskii
Nature Communications 3, 904 (2012)

Electronic mechanism of dipole formation.

Skyrmion rotation

Formation and rotation of skyrmion crystal in the chiral-lattice insulator Cu2OSeO3.
S. Seki, J.-H. Kim, D. S. Inosov, R. Georgii, B. Keimer, S. Ishiwata, and Y. Tokura
Phys. Rev. B 85, 220406 (2012)

(a) Crystal structure of Cu₂OSeO₃ with two distinct Cu²⁺ sites with different oxygen coordination. (b) Proper screw spin order with a single magnetic modulation vector q. (c) Skyrmion crystal with triple magnetic modulation vectors q₁,q₂, and q₃, which lies within a plane normal to the applied magnetic field (H). The background color represents the out-of-plane component of the local magnetic moment (m_z).

Special on DW propagation in nanowires

Spin wave emission in field-driven domain wall motion.
X. S. Wang and X. R. Wang
Phys. Rev. B 90, 184415 (2014)

(a) Schematic diagram of a 1D head-to-head DW (top-left inset) and the snapshot of s components at t=200 for α=0,J=53.7,Dz=0.317,Dz/Dx=10, and H=0.5. Lower-left inset: The s profile of DW. Symbols are numerical results, the vertical dashed line indicates the DW center position at z=0.9, and solid lines are the Walker profile (4) with ϕ=Ht and Z=0.9. Right inset: The simulated motion evolution of the DW center (black curve), the time dependence of the DW center by the collective coordinate model (red curve), and their difference (blue curve). (b) The field dependence of average DW speed v for different Dz and Dx. Vertical dashed and solid lines correspond to critical fields Hc1 and Hc2, respectively. Inset: Simulated DW center for fields below and above Hc1 (indicated by arrows in the main figure).

Domain wall pinning in notched nanowires.
H. Y. Yuan and X. R. Wang

Phys. Rev. B 89, 054423 (2014)

Snapshots of the spin configuration around the notch as the field increases from zero up over the depinning field. (a) H=0 Oe, (b) H=100 Oe, (c) H=170 Oe, and (d) H=180 Oe. For clarity, each spin represents the average magnetization of four 4 × 4 × 4 nm cells. The nanowire dimensions are 1000 × 64 × 4 nm, and the notch dimensions are 40 × 32 × 4 nm. (e) The evolution of m¯zCD and m¯zEF with applied field.

Instability of Walker Propagating Domain Wall in Magnetic Nanowires

B. Hu and X. R. Wang

Phys. Rev. Lett. 111, 027205 (2013)

Illustration of transverse head-to-head DW of width Δ in a nanowire, with easy axis along ẑ and hard axis along x̂. In the absence of external magnetic field (upper), a static DW exists between two domains with m_z=±1. Under a field parallel to the easy axis, the Walker propagating DW moves towards the energy minimum state (m_z=-1) at a speed v while the DW profile is preserved.

Direct Imaging of Thermally Driven Domain Wall Motion in Magnetic Insulators.
Wanjun Jiang, Pramey Upadhyaya, Yabin Fan, Jing Zhao, Minsheng Wang, Li-Te Chang, Murong Lang, Kin L. Wong, Mark Lewis, Yen-Ting Lin, Jianshi Tang, Sergiy Cherepov, Xuezhi Zhou, Yaroslav Tserkovnyak, Robert N. Schwartz, and Kang L. Wang
Phys. Rev. Lett. 110, 177202 (2013)

Experimental demonstration of DW motion driven by a temperature gradient. (a) The schematic illustration of polar MOKE microscope for DW imaging. (b) and (c) M vs H hysteresis loops measured using a MOKE magnetometer for polar and longitudinal orientations, respectively. (d) Snapshots of the position of the DW as a function of time in the cold region, and hot region (e), respectively. It is noted that there is no time correlation between figures (d) and (e). The blue color corresponds to magnetization along +z direction, and white color associates with the magnetization along -z direction. Each fingerlike pattern thus contains two parallel DWs

Domain Wall Propagation through Spin Wave Emission.
X. S. Wang, P. Yan, Y. H. Shen, G. E. W. Bauer, and X. R. Wang
Phys. Rev. Lett. 109, 167209 (2012)

Schematic transverse head-to-head DW of width Δ in a magnetic nanowire. H⃗ is an external field along the wire axis defined as the z direction. DW breathing and other types of periodic DW deformations emit spin waves, denoted by the wavy lines with arrows.

Interactions and size dependence in core/shell Fe NPs

Size Dependence of Inter- and Intracluster Interactions in Core−Shell Iron−Iron Oxide Nanoclusters.
Maninder Kaur, John S. McCloy, Weilin Jiang, Qi Yao, and You Qiang
J. Phys. Chem. C 116, 12875 (2012)

Ferritin for tumors

Magnetoferritin nanoparticles for targeting and visualizing tumour tissues.
Kelong Fan, Changqian Cao, Yongxin Pan, Di Lu, Dongling Yang, Jing Feng, Lina Song, Minmin Liang & Xiyun Yan
Nature Nanotechnology 7, 459 (2012)

Paraffin-embedded clinical tumour tissues, and their corresponding normal and lesion tissues, were stained by FITC-conjugated HFn protein shells and M-HFn nanoparticles. Tumour tissues showed strong positive staining for M-HFn nanoparti…

Tuning EB in core shell NP by defects

1) Monte Carlo simulations of core/shell nanoparticles containing interfacial defects: Role of disordered ferromagnetic spins.
Le Bin Ho, Tran Nguyen Lan, Tran Hoang Hai
Physica B 430, 10 (2013)


2) Defect-tuning exchange bias of ferromagnet/antiferromagnet core/shell nanoparticles by numerical study.
Zhongquan Mao, Xiaozhi Zhan and Xi Chen

J. Phys.: Condens. Matter 24, 276002 (2012)

Ferritin: A review

Ferritin: A Versatile Building Block for Bionanotechnology.
Günther Jutz, Patrick van Rijn, Barbara Santos Miranda, and Alexander Böker
Chemical Reviews 25, 1653 (2015)

Time resolved relaxation of nanomagnet

Time-resolved magnetic relaxation of a nanomagnet on subnanosecond time scales.
H. Liu, D. Bedau, J. Z. Sun, S. Mangin, E. E. Fullerton, J. A. Katine, and A. D. Kent
Phys. Rev. B 85, 220405 (2012)

(a) The total switching probability P_AP→P^double as a function of the second-pulse duration t₂ for a current I₁ of 8.5 mA and different delays. The dashed line is the switching probability P_AP→P⁽²⁾ for a single 8.5 mA pulse of duration t₂. (b) The same data are plotted with shifted time axis, with the shift dependent on the delay δt(t_delay). The data closely overlap, showing that the switching probability of a double pulse (t₁+t_delay+t₂) is the same as that of a single pulse with a longer duration, i.e., t₂+δt(t_delay), as illustrated schematically by the pulses drawn within the figure.

Magnetization reversal in nanodisks

Magnetization reversal by confined droplet growth in soft/hard hybrid nanodisks with perpendicular anisotropy.
J.-P. Adam, S. Rohart, J.-P. Jamet, J. Ferré, A. Mougin, R. Weil, H. Bernas, and G. Faini
Phys. Rev. B 85, 214417 (2012)

(a) Expected spontaneous magnetization M_s variation along the nanodisk radius. (b) PMOKE image difference between the remnant state after a magnetic field pulse (27 mT, 200 ns) and the remnant state after saturation under 500 mT during 5 s.

Interacting AF NPs

Magnetic behaviour of interacting antiferromagnetic nanoparticles.
 V Markovich, R Puzniak, Y Skourski, A Wisniewski, D Mogilyanski, G Jung and G Gorodetsky
J. Phys.: Condens. Matter 24, 266001 (2012)

Electric control of DW velocity

Electric-field control of magnetic domain-wall velocity in ultrathin cobalt with perpendicular magnetization.
D. Chiba, M. Kawaguchi, S. Fukami, N. Ishiwata, K. Shimamura, K. Kobayashi, & T. OnoNature Communications 3, 888 (2012)

Device structure and measurement configuration. A schematic diagram of the device structure and the measurement configuration. The device consisted of a Co/Pt microwire, a HfO₂ dielectric layer, and a gate electrode on top.

Controlling AF Spin Waves

Coherent terahertz control of antiferromagnetic spin waves.
Tobias Kampfrath, Alexander Sell, Gregor Klatt, Alexej Pashkin, Sebastian Mährlein, Thomas Dekorsy, Martin Wolf, Manfred Fiebig, Alfred Leitenstorfer & Rupert Huber Nature Photonics 5, 31 (2011)

a, Crystal lattice of NiO (blue spheres, Ni²⁺; yellow spheres, O^2–) with magnetically ordered spins (blue arrows) of a selected S domain in the (111) planes (light blue) and the direction of the terahertz magnetic field B (double-ended…

Quantum Strings in Quantum Spin Ice.

Quantum Strings in Quantum Spin Ice.
Yuan Wan and Oleg Tchernyshyov
Phys. Rev. Lett.108, 247210 (2012)

(a) The checkerboard lattice. A and B denote two symmetrically inequivalent planar tetrahedra, and arrows, the local ẑ_i directions. (b) The fully polarized state when the field is applied in the c direction. Arrows denote the spin orientations. (c) A string of flipped spins (light green) binding a Q=+1 monopole (red solid circle) and a Q=-1 one (open blue circle). (d)–(f) -ImS^aa(ω,k) for k_b=0. B/h=0.5, 1.5, and 4.5, respectively.

Ultrafast switching of AF and FiM

THz Switching of Antiferromagnets and Ferrimagnets.
S. Wienholdt, D. Hinzke, and U. Nowak
Phys. Rev. Lett. 108, 247207 (2012)

Excitation of an antiferromagnet with a ps magnetic field pulse. (a) l_z shows inertial behavior. (b) Excitation triggers inertial switching. (c) Energies during switching process.

Magnetic Vortex Nanorings: application to hysperthermia and simulations

Some recent articles related to the proposal of using Fe oxide nanorings for magnetic hyperthermia.

1) Magnetic Vortex Nanorings: A New Class of Hyperthermia Agent for Highly Efficient In Vivo Regression of Tumors.
Xiao Li Liu, Yong Yang, Cheng Teng Ng, Ling Yun Zhao, Ying Zhang, Boon Huat Bay, Hai Ming Fan, and Jun Ding
Advanced materials 27, 1939 (2015)

The unique magnetic vortex structure allows ferrimagnetic vortex-domain iron oxide nanorings to possess negligible remanence and large hysteresis loss, which not only promotes colloid stability but also maximizes the specific absorption rate. It overcomes the super-paramagnetic limitation and allows a new class of nanoparticle agent to be designed for high-performance thermal-based biomedical applications.

2) Innovative magnetic nanoparticle platform for magnetic resonance imaging and magnetic fluid hyperthermia applications
Xiao Li Liu, Hai Ming Fan
Current Opinion in Chemical Engineering 4, 38 (2014)

Illustration of representative NP agent comprised of magnetic core and shell coating for biorelated applications.

3) Stable vortex magnetite nanorings colloid: Micromagnetic simulation and experimental demonstration.
Yong Yang, Xiao-Li Liu, Jia-bao Yi, Yang Yang, Hai-Ming Fan, and Jun Ding
J. Appl. Phys. 111, 044303 (2012)

(a)-(c) The simulated ground states (F_out, vortex, and onion, respectively) of magnetite nanorings with different geometry. (d) Ground state phase diagram of magnetite nanorings as a function of T and D_out with β = 0.8 (black triangles), 0.6 (red squares), and 0.4 (blue circles). Solid symbols show the boundaries between the vortex, F_out (out-of-plane ferromagnetic) and F_in (in-plane ferromagnetic) configurations.

Vortices in nano objects

Stabilizing Vortices in Interacting Nano-Objects: A Chemical Approach.Lise-Marie Lacroix, Sébastien Lachaize, Florian Hue, Christophe Gatel, Thomas Blon, Reasmey P. Tan, Julian Carrey, Bénédicte Warot-Fonrose, and Bruno Chaudret
Nano Letters12, 3245 (2012)

We report a chemical method to prepare metallic Fe porous nanocubes. The presence of pores embedded inside the cubes was attested by electron tomography. Thanks to electronic holography and micromagnetic simulations, we show that the presence of these defects stabilizes the vortices in assembly of interacting cubes. These results open new perspectives toward magnetic vortex stabilization at relatively low cost for various applications (microelectronics, magnetic recording, or biological applications).

Giant magnetocaloric effect by structural transitions

Giant magnetocaloric effect driven by structural transitions
Jian Liu, Tino Gottschall, Konstantin P. Skokov, James D. Moore & Oliver Gutfleisch
Nature Materials 11, 620 (2012)

Contributions from the magnetic and structural part for a first-order magnetic transition to the MCE.Schematic shows Ni–Mn-based Heusler alloys as an example. Alignment of magnetic moments by adiabatic magnetization results in the sample heating up (top row); simultaneously the structural transition from low-magnetization and twinn…

Bloch point structure

Bloch point structure in a magnetic nanosphere.
Oleksandr V. Pylypovskyi, Denis D. Sheka, and Yuri Gaididei
Phys. Rev. B 85, 224401 (2012)

Dynamics of total spin along the z axis of the sample. The Bloch point is initially shifted by Δz=−2a₀ from the center of the sample. The insets show magnetization distribution in z=−0.5a₀ and y=−0.5a₀ planes for different times. The color bar indicates S_z,n for different lattice nodes.

Thermally assisted STT reversal

Thermally assisted spin-transfer torque magnetization reversal in uniaxial nanomagnets.
D. Pinna, Aditi Mitra, D. L. Stein and A. D. Kent
Appl. Phys. Lett. 101, 262401 (2012)

Mean switching time versus current in the sub-critical low current regime (I<1).

Magnetic NP for Cancer Diagnosis: Review

Special issue on Magnetic Nanoparticles for Biomedical Applications.

Magnetic Nanoparticles for Cancer Diagnosis and Therapy.
Mehmet V. Yigit & Anna Moore & Zdravka Medarova
Pharm Res (2012) 29:1180–1188

MQT in a free NP

Quantum tunneling of the magnetic moment in a free nanoparticle.
M.F. O'Keeffe, E.M. Chudnovsky, D.A. GaraninJMMM 324, 2871 (2012)

Dependence of energy on J at K=J   and _Iz/_Ix=2$I_z/I_x=2$ for different values of α$\alpha$. The plot shows first-order quantum phase transition on α$\alpha$.

Hyperthermia and dipolar interactions in Fe-MgO NPs

Adjustable Hyperthermia Response of Self-Assembled Ferromagnetic Fe-MgO Core–Shell Nanoparticles by Tuning Dipole–Dipole Interactions.
Carlos Martinez-Boubeta, Konstantinos Simeonidis, David Serantes, Iván Conde-Leborán, Ioannis Kazakis, George Stefanou, Luis Peña, Regina Galceran, Lluis Balcells, Claude Monty, Daniel Baldomir, Manassis Mitrakas and Makis Angelakeris
Advanced Funtional Materials 22, 3737 (2012)

The correlations arising from dipole–dipole interactions and their influence on the hyperthermia efficacy are studied both theoretically and experimentally and found to be in quantitative agreement. The calculation represents an analytical model of hyperthermia in magnetic interacting particle systems to explain in a simple way the ubiquitous behavior observed in this class of materials.

Hybrid NP for cancer: Review

Hybrid Nanoparticles for Detection and Treatment of Cancer.
Michael J. Sailor and Ji-Ho ParkAdvanced Materials 28, 3779 (2012)

EB of magnetoelectronic materials

Exchange biasing of magnetoelectric composites.
Enno Lage, Christine Kirchhof, Viktor Hrkac, Lorenz Kienle, Robert Jahns, Reinhard Knöchel,  Eckhard Quandt & Dirk Meyners Nature Materials 11, 523 (2012)

Z-contrast image of the Fe₅₀Co₅₀ multilayer system on a AlN substrate (right-hand side of the image, columnar grown) and a magnified view (inset) with a line indicating the selected area for chemical analysis

SW excitation by STT

Spin-Wave Excitation in Magnetic Insulators by Spin-Transfer TorqueJiang Xiao and Gerrit E. W. Bauer
Phys. Rev. Lett. 108, 217204 (2012)

An electrically insulating magnetic film of thickness d with magnetization m (∥ẑ at equilibrium) in contact with a normal metal. A spin current J_s∥ẑ is generated in the normal metal and absorbed by the ferromagnet.

Magnetometer in pigeons

An Avian Magnetometer
Michael Winklhofer
Science 336, 991 (2012)

Glas transition in dipolar magnets?

Unreachable glass transition in dilute dipolar magnet.
A. Biltmo & P. Henelius ncomms1857.pdf (application/pdf Object)

The experimental data (black dots) are from Quilliam et al.¹³, whereas red lines are best fits to equation (3) at temperatures 0.10, 0.11, 0.12, 0.14, 0.15, 0.17 and 0.20 K from left to right.

Magnetic DW Injector

Highly Efficient In-Line Magnetic Domain Wall Injector.
Timothy Phung, Aakash Pushp, Luc Thomas, Charles Rettner, See-Hun Yang, Kwang-Su Ryu, John Baglin, Brian Hughes, and Stuart Parkin

Nano Letters 15, 835 (2015)

We demonstrate a highly efficient and simple scheme for injecting domain walls into magnetic nanowires. The spin transfer torque from nanosecond long, unipolar, current pulses that cross a 90° magnetization boundary together with the fringing magnetic fields inherently prevalent at the boundary, allow for the injection of single or a continual stream of domain walls. Remarkably, the currents needed for this “in-line” domain wall injection scheme are at least one hundred times smaller than conventional methods.

Trapping skyrmions in a hole

Capturing of a magnetic skyrmion with a hole.
Jan Müller and Achim Rosch

Phys. Rev. B 91, 054410 (2015)

Snapshot of a micromagnetic simulation of skyrmion driven by a current (D=0.3J/a, μB=0.09J/a2, vs=0.001aJex, and α=β=0.4) in the presence of a single vacancy: a missing spin (gray sphere). The trajectory of the skyrmion center is indicated by a red line.

Spin waves in Heisenberg AF

Spin-wave multiple excitations in nanoscale classical Heisenberg antiferromagnets.
Zhuofei Hou and D. P. Landau, G. M. Stocks, G. Brown

Phys. Rev. B 91, 064417 (2015)

The spectra for ST(r0,q,ω) obtained from isotropic, antiferromagnetic nanofilms with the same Lxy=20 and three different thicknesses, i.e., Lz=10, 20, and 30. The results were obtained in the PBCXY [100] directions, i.e., the directions parallel to the free surfaces, with r0⇒bulkcenter at T=0.4TN with SD parameters of nt=5000,ncutoff=4000, and dt=0.2/|J|. We give the spectra for nq=0,1,2,...,5. N is the total number of initial configurations.

Nonmonotonic residual entropy in diluted spin ice: A comparison between Monte Carlosimulations of diluted dipolar spin ice models and experimental results.
T. Lin, X. Ke, M. Thesberg, P. Schiffer, R. G. Melko, and M. J. P. Gingras

Phys. Rev. B 90, 214433 (2014)

Spin Spirals in Mn

Thermal properties of a spin spiral: Manganese on tungsten (110)
G. Hasselberg, R. Yanes, D. Hinzke, P. Sessi, M. Bode, L. Szunyogh, and U. Nowak

Phys. Rev. B 91, 064402 (2015)

Sketch of the calculated DM vectors Dij up to the fifth NN shell of the 2D lattice formed by the Mn atoms. The DM vectors (grey arrows) are placed at the center of the line connecting the center atom (red sphere) and its corresponding neighbor (green sphere). The length of the DM vector is proportional to its magnitude and also reflects the orientation in space. Note the rapid decay in the magnitude of DM vectors with distance; see also Fig. 1. Green arrows represent the magnetic moment.