Switch from Bloch to Nèel DWs

Analytic theory for the switch from Bloch to Néel domain wall in nanowires with perpendicular anisotropy
M. D. DeJong and K. L. Livesey
Phys. Rev. B 92, 214420 (2015)

(a) The geometry of a rectangular nanowire with perpendicular magnetic anisotropy, width w and thickness d. Arrows show the direction of magnetization. Depending on the size of w and d, the lowest energy domain wall may be of (b) Bloch or (c) Néel type. In the Bloch wall, the magnetization rotates perpendicular to the wire's long z axis, in the x−y plane. In the Néel wall, the magnetization rotates along the wire's long z axis, in the y−z plane.

Magnetization dynamics in individual magnetite nanocrystals

Probing magnetization dynamics in individual magnetite nanocrystals using magnetoresistive scanning tunneling microscopy.
Amir Hevroni, Boris Tsukerman, and Gil Markovich
Phys. Rev. B 92, 224423 (2015)

(a), (d), and (g) Current vs time measurements performed on the three particles. Each particle was examined at a different temperature (indicated on the figure). In the case of particle 3, the graph shown is one of five consecutive measurements. (b), (e), and (h) Constant current STM topography images of the three particles. (c), (f), and (i) Height profiles of the measured particles, which are marked by arrows.

Small is Smarter: Nano MRI Contrast Agents – Advantages and Recent Achievements - Gao - 2015 - Small - Wiley Online Library

Small is Smarter: Nano MRI Contrast Agents – Advantages and Recent Achievements.

Zhenyu Gao, Tiancong Ma, Enyu Zhao, Dominic Docter, Wensheng Yang, Roland H. Stauber and Mingyuan Gao

Small 12, 556 (2015)

Magnetic nanoparticles hold great potential as contrast agents for magnetic resonance imaging and advanced applications in multimodality imaging and drug carriers for cancer thranostics. To promote the development of this field, state-of-the-art achievements are summarized and fundamental scientific challenges are discussed

Magnetization reversal of an individual exchange-biased permalloy nanotube

Magnetization reversal of an individual exchange-biased permalloy nanotube.

A. Buchter, R. Wölbing, M. Wyss, O. F. Kieler, T. Weimann, J. Kohlmann, A. B. Zorin, D. Rüffer, F. Matteini, G. Tütüncüoglu, F. Heimbach, A. Kleibert, A. Fontcuberta i Morral, D. Grundler, R. Kleiner, D. Koelle, and M. Poggio

Phys. Rev. B 92, 214432 (2015)

Training effect: (a) SQUID and (b) DCM hysteresis loops for different loop number n at T=3.4 K. Red and blue curves indicate up- and down-sweep, respectively. Evolution of (c) exchange field and (d) coercivity with increasing loop number n extracted from SQUID data set. Dashed line fits the data according to Eq. (2). Point size corresponds to the measurement error in field

Chiral damping of DWs

Chiral damping of magnetic domain walls.

Emilie Jué, C. K. Safeer, Marc Drouard, Alexandre Lopez, Paul Balint, Liliana Buda-Prejbeanu, Olivier Boulle, Stephane Auffret, Alain Schuhl, Aurelien Manchon, Ioan Mihai Miron & Gilles Gaudin

Nature Materials AOL (2015)

Graphic illustration of the asymmetric DW dynamics in PMA materials.

Fundamentals and advances in magnetic hyperthermia

Fundamentals and advances in magnetic hyperthermia.

E. A. Périgo, G. Hemery, O. Sandre, D. Ortega, E. Garaio, F. Plazaola and F. J. Teran

Appl. Phys. Rev. 2, 041302 (2015)

(a) 3D scatter plot showing the main experimental conditions reported in a set of 120 publications on MH spanning over the last 25 years. Scatter size is proportional to the H0·f product. Green dots of different intensities are the 2D projection of the central scatter over the XY, XZ, and YZ planes. The color code of the spheres is related to the type of assay described in the corresponding publication: red refers to in vivo tests, yellow to in vitro tests, blues to combined in vivo/in vitro tests, and cyan to SAR measurements. The dashed black curve superimposed to the field intensity vs maximum frequency plane indicates the “Brezovich” or H0·f criterion, along which the H0·f = 4.8 × 10⁸ A(ms)⁻¹ condition is fulfilled [note that the experiments complying with this criterion are those below the curve]. (b) Zoom of the most populated region of (a), where the concentration of SAR measurements in the 2005–2009 period an in vivo tests in the 2010–2015 period is shown.

 

Classical and quantum dynamics of molecular spins on graphene

The classical and quantum dynamics of molecular spins on graphene.

Christian Cervetti, Angelo Rettori, Maria Gloria Pini, Andrea Cornia, Ana Repollés, Fernando Luis, Martin Dressel, Stephan Rauschenbach, Klaus Kern, Marko Burghard, Lapo Bogani

Nature Materials 15, 164 (2016)

a, |m_s sublevels of the ground state of the single-molecule-magnet [Fe₄(L)₂(dpm)₆], as obtained from equation (1). Absorption of phonons allows the barrier to be thermically overcome (green arrows). W ± n indicate the transition probabilities between magnetic |m states induced by the absorption (+) or emission (−) of n phonons. Quantum tunnelling happens between admixed levels (red arrows), whereas hyperfine and dipolar interactions create energy distributions (orange). Interaction with Dirac electrons increases the tunnel splittings below |3 and |−3 (red areas, exaggerated for clarity). b, Temperature and frequency dependence of the imaginary component of the dynamic susceptibility (χ′′) in a magnetic field H = 1 kOe for [Fe₄(L)₂(dpm)₆] (top) and hybrids with isolated molecules (bottom). Lines are simulations with the theory (see text for the theory). c, Temperature and frequency dependence of the real component of the dynamic susceptibility (χ′) in H = 0 for [Fe₄(L)₂(dpm)₆] (top) and hybrids with isolated molecules (bottom). Lines are simulations with the theory (see text for the theory).

Origin of perpendicular anisotropy in Fe atoms

Origin of Perpendicular Magnetic Anisotropy and Large Orbital Moment in Fe Atoms on MgO.

S. Baumann, F. Donati, S. Stepanow, S. Rusponi, W. Paul, S. Gangopadhyay, I. G. Rau, G. E. Pacchioni, L. Gragnaniello, M. Pivetta, J. Dreiser, C. Piamonteze, C. P. Lutz, R. M. Macfarlane, B. A. Jones, P. Gambardella, A. J. Heinrich, and H. Brune

Phys. Rev. Lett. 115, 237202 (2015)

(a) STM image of two Fe atoms on a ML MgO(100) grown on Ag(100) (4  nm×4  nm, tunnel current It=5  pA, tunnel voltage Vt=100  mV). (b) Side view of DFT-calculated binding geometry and charge density [color scale, 1e/(au)3; Fe, green; O, red; Mg, blue). (Middle sketch) Top view ball model of the binding geometry. (c) Oblique view of DFT-calculated valence electron spin density contours (positive spin polarization, red; negative, blue).

Spin-glass-like freezing of inner and outer surface layers in hollow γ-Fe2O3 nanoparticles

Spin-glass-like freezing of inner and outer surface layers in hollow γ-Fe2O3 nanoparticles.

Hafsa Khurshid, Paula Lampen-Kelley, Òscar Iglesias, Javier Alonso, Manh-Huong Phan, Cheng-Jun Sun, Marie-Louise Saboungi & Hariharan Srikanth

Scientific Reports 5, 15054 (2015) 

Snapshots of the outer and inner surface spin configurations subject to varying magnetic fields (a) h = 100 (the maximum positive applied field), (b) h = 0 (remanence at the upper branch), (c) h = −25 (near the negative coercive field), and (d) h = −100 (the maximum negative applied field). Spins have been colored with a gradient from dark-red/dark-blue (outer/inner surface) for spins along the field direction to yellow/green (outer/inner surface) for spins transverse to the field direction. Only a slice of the spin configurations of a hollow nanoparticle close to the central plane and perpendicular to the field direction is shown.

Hysteresis of quantum uniaxial superparamagnets

Nonlinear ac stationary response and dynamic magnetic hysteresis of quantum uniaxial superparamagnets.

Yuri P. Kalmykov, Serguey V. Titov, and William T. Coffey

Phys. Rev. B 92, 174414 (2015)

DMH loops [m(t)=⟨SˆZ⟩(t)/S vs h(t)=cosωt] for various anisotropy parameters σ=10 (a), 15 (b), 20 (c), and various spin numbers S=3/2 (1: short-dashed lines), 4 (2: solid lines), 10 (3: dashed-dotted lines), 20 (4: dashed lines), and ∞ (asterisks) at ωτN=10−4, ξ0=0, and ξ=9.

A magnetic protein biocompass

A magnetic protein biocompass.

Siying Qin, Hang Yin, Celi Yang, Yunfeng Dou, Zhongmin Liu, Peng Zhang, He Yu, Yulong Huang, Jing Feng, Junfeng Hao, Jia Hao, Lizong Deng, Xiyun Yan, Xiaoli Dong, Zhongxian Zhao, Taijiao Jiang, Hong-Wei Wang, Shu-Jin Luo & Can Xie

Nature Materials 15,217 (2016)

The biocompass model of animal magnetoreception and navigation.

Enhancing the magnetic anisotropy of maghemite nanoparticles via the surface coordination of molecular complexes : Nature Communications : Nature Publishing Group

Enhancing the magnetic anisotropy of maghemite nanoparticles via the surface coordination of molecular complexes.

Yoann Prado, Niéli Daffé, Aude Michel, Thomas Georgelin, Nader Yaacoub, Jean-Marc Grenèche, Fadi Choueikani, Edwige Otero, Philippe Ohresser, Marie-Anne Arrio, Christophe Cartier-dit-Moulin, Philippe Sainctavit, Benoit Fleury, Vincent Dupuis, Laurent Lisnard, Jérôme Fresnais

Nature Communications 6, 10139 (2015)

(a) Field-cooled and zero-field-cooled (FC/ZFC) magnetization curves measured in the 5–80 K temperature range under an applied field of 50 Oe and (b) magnetization vs field curves measured at 5 K for 0b and 1 in diluted solutions.

Criteria for saturated magnetization loop

Criteria for saturated magnetization loop.

A. Harres, M. Mikhov, V. Skumryev, A.M.H. de Andrade, J.E. Schmidt, J. Geshev

J. Magn. Magn. Mater.402, 76 (2015)

M(H  ) loops calculated for a disordered system of non-interacting single-domain uniaxial-anisotropy particles using $H_{\max }^{+}/H_{\mathrm{A}}=1.2$, where $H_{\max }^{-}/H_{\mathrm{A}}=-1.2$ (panel (a)) and $H_{\max }^{-}/H_{\mathrm{A}}=-0.8$ (panel (b)). The first (panels (c) and (d)) and the second (panels (e) and (f)) derivatives of the respective descending and ascending branches for negative fields are also given. Although $H_{\max }^{+}/H_{\mathrm{A}}=1.2$ for both loops and their derivatives, only the regions of interest are plotted. The bottom panels show the −m_d(H)$-m_{\mathrm{d}}\left(H\right)$ and m_r(H)$m_{\mathrm{r}}\left(H\right)$ (the latter obtained starting from a random magnetization state) remanence curves; the first derivatives of −m_d(H)$-m_{\mathrm{d}}\left(H\right)$ are plotted in the insets.

Enhancing the magnetic anisotropy of maghemite nanoparticles via the surface coordination of molecular complexes : Nature Communications : Nature Publishing Group

Enhancing the magnetic anisotropy of maghemite nanoparticles via the surface coordination of molecular complexes.

Yoann Prado, Niéli Daffé, Aude Michel, Thomas Georgelin, Nader Yaacoub, Jean-Marc Grenèche, Fadi Choueikani, Edwige Otero, Philippe Ohresser, Marie-Anne Arrio, Christophe Cartier-dit-Moulin, Philippe Sainctavit, Benoit Fleury, Vincent Dupuis, Laurent Lisnard; Jérôme Fresnais

Nature Communications 6, 10139 (2015)

(a) Representation of the [Co(TPMA)Cl₂] complex used to enhance the magnetic anisotropy of the γ-Fe₂O₃ nanoparticles. (b) TEM image of the γ-Fe₂O₃ nanoparticles functionalized with the cobalt(II) complex: 1 (5.0 nm, σ=0.09) and (c) schematic view of the coordination of the complex with the iron ions. (d) Synthesis scheme with measured pH values, hydrodynamic diameters (Z_av), sizes (D) and distributions (σ).

Tuning the magnetic anisotropy in coordination nanoparticles: random distribution versus core–shell architecture.

Yoann Prado, Nada Dia, Laurent Lisnard, Guillaume Rogez, François Brisset, Laure Catala and   Talal Mallah

Chem. Commun. 48, 11455 (2012)

Core–shell magnetic coordination nanoparticles made of a soft core and a hard magnetic shell, containing anisotropic Co(II) ions, display a dramatic increase in their average blocking temperature with a coercive field value 25 times larger than that of the soft core, due to a large enhancement of the magnetic anisotropy.

Competing domains in EB nanostrucutres

Manipulation of competing ferromagnetic and antiferromagnetic domains in exchange-biased nanostructures.
Arantxa Fraile Rodríguez, Ali C. Basaran, Rafael Morales, Miroslavna Kovylina, Jordi Llobet, Xavier Borrisé, Matthew A. Marcus, Andreas Scholl, Ivan K. Schuller, Xavier Batlle, and Amílcar Labarta
Phys. Rev. B 92, 174417 (2015)

Fraction of inverted domains for Ni(6nm)/FeF2(70nm) as a function of the AD, measured at zero field and 30 K, upon ZFC from 296 K (red) and FC (black; HFC=50Oe from 200 K to 45 K and HFC=0Oe from 45 K to 30 K). The error bars represent the standard deviation over up to 15 independent measurements. The occasional data points where no error bar is given refer as to cases where a comparable statistics is not available. The dashed lines are guides to the eye.

Stability of skyrmionic bits

Stability of single skyrmionic bits.
J. Hagemeister, N. Romming, K. von Bergmann, E. Y. Vedmedenko & R. Wiesendanger
Nature Communications 6, 8455 (2015)

(a) Triangular spin lattice with a hexagonal boundary shape containing a single skyrmion at k_BT=0.05 J and μB=0.1 J. (b) The inset displays the DM energy as a function of the Monte Carlo step (MCS) for different magnetic field strengths at k_BT=0.61 J exhibiting a two-state behaviour due to the ongoing creation and annihilation of a single skyrmion. The size of the system is such that it contains a maximum of one skyrmion at a given MCS. The histogram of the DM energy shows two peaks corresponding to the FM and Sk states. The Sk and FM states are populated with equal probability at the critical field B_c and the areas underneath the peaks of the histogram are equal.

Inertia in spin dynamics

Spin dynamics with inertia in metallic ferromagnets.

Toru Kikuchi and Gen Tatara

Phys. Rev. B 92, 184410 (2015)

(a) Without any magnetic field, the general motion of spin with finite inertia is a free precession motion, just like a spinning top. The spin Sn precesses around the total angular momentum j0. (b) When a constant magnetic field B is applied, the total angular momentum j0 precesses around B. Therefore the “free precession cone” in (a) precesses around B as a whole, which corresponds to the Larmor precession in the absence of the inertia. What was called the free precession in (a) is now called the nutation.

 

Switching of exchange coupled grains

Thermally activated switching at long time scales in exchange-coupled magnetic grains.

Ahmad M. Almudallal, J. I. Mercer, J. P. Whitehead, M. L. Plumer, J. van Ek, and T. J. Fal

Phys. Rev. B 92, 134418 (2015)

The contour plot of the minimum energy surface for the weak coupling case I=0.5×10−3J/m2 for (a) H=0 and (b) H=4kOe. The black lines indicate the boundary separating each pair of basins of attraction {Ωα,Ωβ} and is denoted by Γαβ. The red lines indicate the MEP connecting the four minima. The lines cross at the saddle points sαβ.

2D Nanomaterials: Review

Ultrathin Two-Dimensional Nanomaterials.
Hua Zhang
ACS Nano 9, 9451 (2015)

 

Review: Magnetic nanoparticles: applications in biomedicine

Magnetic nanoparticles: material engineering and emerging applications in lithography and biomedicine.
Yuping Bao, Tianlong Wen, Anna Cristina S. Samia, Amit Khandhar, Kannan M. Krishnan
Journal of Materials Science 51, 513 (2016) 

Spin configurations in a single Fe cube

Size-Specific Spin Configurations in Single Iron Nanomagnet: From Flower to Exotic Vortices.

Christophe Gatel, Francisco Javier Bonilla, Anca Meffre, Etienne Snoeck, Bénédicte Warot-Fonrose, Bruno Chaudret, Lise-Marie Lacroix, and Thomas Blon

Nano Letters 15, 6952 (2015)

From shape to surface effects in magnetic anisotropy of Co NPs

Size effects in the magnetic anisotropy of embedded cobalt nanoparticles: from shape to surface.
Simón Oyarzún, Alexandre Tamion, Florent Tournus, Véronique Dupuis, Matthias Hillenkamp

Scientific Reports 5, 14749 (2015)

Comparison of the experimental values for with the magnetic surface anisotropy calculated using the Néel model for different example cluster sizes and single facets added along the [100] (blue, lower curve) and [111] (green, upper curve) directions.

Iron Oxide NPs for Multimodal Imaging and Magnetoresponsive Therapy

Iron Oxide Based Nanoparticles for Multimodal Imaging and Magnetoresponsive Therapy.
Nohyun Lee, Dongwon Yoo, Daishun Ling, Mi Hyeon Cho, Taeghwan Hyeon, and Jinwoo Cheon 
Chem. Rev. 115, 10637 (2015)
 

Néel skyrmions in confined geometries

Degeneracies and fluctuations of Néel skyrmions in confined geometries.
Rick Keesman, A. O. Leonov, P. van Dieten, Stefan Buhrandt, G. T. Barkema, Lars Fritz, and R. A. Duine 
Phys. Rev. B 92, 134405 (2015)

Simulations snapshots of spin systems of size L×L=3 for different parameter values and temperatures with the parameter D/Jchosen such that the pitch length p=8. The periodic boundary is drawn as a red solid line and spin vectors are represented by colored arrows where the color scales linearly with the zˆ component of the vector to highlight spin texture