Equilibrium magnetization and magnetization relaxation of multicore magnetic nanoparticles

Equilibrium magnetization and magnetization relaxation of multicore magnetic nanoparticles.
Patrick Ilg
Phys. Rev. B 95, 214427 (2017)

Left: Visualization of a dense random cluster containing $N=100$ nanoparticles prepared as described in Sec. 3a. Right: Visualization of a cluster containing $N=100$ nanoparticles prepared by DLCA with $Q_{\mathrm{dd}}=2$ and $\varepsilon =4$ as described in Sec. 3b.

DW annhilation in wires

Annihilation of domain walls in a ferromagnetic wire.

Anirban Ghosh, Kevin S. Huang, and Oleg Tchernyshyov

Phys. Rev. B 95, 180408(R) (2017)

Several configurations of a pair of domain walls with shown values of separation $\zeta$ and twist $\phi$. The red and blue colors denote positive and negative magnetization component $m_z$ along the axis of the cylinder. The wire frames depict the local plane tangential to the magnetization field. Spheres on the right show the path of the magnetization field $m\left(z\right)$ as $z$ goes from $-\infty$ to $+\infty$, beginning from and ending at the north pole (red). The south pole (blue) can only be reached if the separation of the domain walls $\zeta =\infty$.

Thermally activated helicity reversals of skyrmions

Thermally activated helicity reversals of skyrmions.
X. Z. Yu, K. Shibata, W. Koshibae, Y. Tokunaga, Y. Kaneko, T. Nagai, K. Kimoto, Y. Taguchi, N. Nagaosa, and Y. Tokura
Phys. Rev. B 93, 134417 (2016)

Schematic of a bubble with winding number 1. Arrows show that the magnetic moments and concentric rings are a bubble domain wall. ϕ, φ, and ψ denote the polar angle, azimuthal angle, and the angle between the magnetic moment and the $x$ direction, respectively.

Chirality-Dependent Transmission of SW through DW

Chirality-Dependent Transmission of Spin Waves through Domain Walls.
F. J. Buijnsters, Y. Ferreiros, A. Fasolino, and M. I. Katsnelson
Phys. Rev. Lett. 116, 147204 (2016)

Effect of the interfacial DMI on the magnetization profile $m\left(x\right)$ of a DW in a thin film with perpendicular anisotropy. (a) Away from the DW, magnetization points out of the film ($\hat{z}$ or $-\hat{z}$). Near the DW, the DMI creates an effective field $H_{\mathrm{DMI}}$ in the $-\hat{x}$ direction. Depending on the competition between the dipolar and DMI interactions, the equilibrium configurations circle, circle prime, star, star prime, and square, shown in (b)–(d), are possible. (b) Without DMI, the minimum-energy configurations (flux closure) are two equivalent Bloch DWs (circle, in dark colors, and circle prime, in light colors), whose in-plane orientations differ by 180°. (c) For intermediate DMI, the minimum-energy configurations are intermediate between Bloch and Néel. There are two equivalent minimum-energy states (star and star prime), whose in-plane orientations differ by approximately 90° for an appropriately tuned DMI strength $D$. (d) For strong DMI, a single minimum-energy configuration (square) exists: a Néel DW with magnetization in the center pointing in the $-\hat{x}$ direction.

Antiferromagnetic Skyrmions: Applied Current and Temperature

Static and Dynamical Properties of Antiferromagnetic Skyrmions in the Presence of Applied Current and Temperature.
Joseph Barker and Oleg A. Tretiakov
Phys. Rev. Lett. 116, 147203 (2016)

The spin texture of a $G$-type AFM Skyrmion. (a) Top view of the Skyrmion, white lines show contours of constant $n_z$. The radius is 2.1 nm. (b) Cross section of the Skyrmion. The core is not a single spin but a compensated structure combining the two sublattices.

Ultrafast dynamics in FePt

Modeling of Ultrafast Heat- and Field-Assisted Magnetization Dynamics in FePt

P. Nieves and O. Chubykalo-Fesenko

Phys. Rev. Applied 5, 014006 (2016)

Snapshots of the system magnetization state in the continuous film with F=40  mJ/cm3 and μ0Hz=−3  T at time moments (a) t=0.25  ns, (b) t=0.5  ns, (c) t=3.2  ns, and (d) t=3.6  ns. The figures show an area of 150×150  nm.

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.

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.

 

Neel and Brownian relaxation in NPs by ac field

Mixed Brownian alignment and Néel rotations in superparamagnetic iron oxide nanoparticle suspensions driven by an ac field.

Saqlain A. Shah, Daniel B. Reeves, R. Matthew Ferguson, John B. Weaver, and Kannan M. Krishnan
Phys. Rev. B 92, 094438 (2015)

Comparison between simulation and experiment for nanoparticles either in either a frozen or melted state. Spectroscopy was performed with a 26-kHz, 31 mT/μ0 field. The log-normal distributions of particle diameter and anisotropy constant are shown on the right by number in a representative 1000-particle subsample.

 

Dynamically stabilized magnetic skyrmions

Dynamically stabilized magnetic skyrmions.

Y. Zhou, E. Iacocca, A. A. Awad, R. K. Dumas, F. C. Zhang, H. B. Braun and J. Åkerman
Nature Communications 6, 8193 (2015)

(a) A bubble skyrmion stabilized by dipolar interactions which may exist as a left- or right-handed version. Its size typically exceeds that of skyrmions stabilized by DMI. (b,c) DMI stabilized skyrmions: (b) A chiral skyrmion as favoured in B20-type materials such as MnSi. (c) A hedgehog skyrmion as favoured by interfacial DMI.(d) Dynamically stabilized magnetic skyrmion which requires neither dipolar interactions nor DMI and which exhibits precession around the (vertical) easy-axis anisotropy. (e) For vanishing dipolar interactions (DDI), DMI and Oe fields, and in absence of damping, the skyrmion precesses uniformly and breathing disappears.

LLBar phenomenological relaxation equation

Phenomenological description of the nonlocal magnetization relaxation in magnonics, spintronics, and domain-wall dynamics.

Weiwei Wang, Mykola Dvornik, Marc-Antonio Bisotti, Dmitri Chernyshenko, Marijan Beg, Maximilian Albert, Arne Vansteenkiste, Bartel V. Waeyenberge, Andriy N. Kuchko, Volodymyr V. Kruglyak, and Hans Fangohr

Phys. Rev. B 92, 054430 (2015)

The spin-wave-amplitude decay along the rod, for a spin wave excited locally by applying a microwave H=H0sin(2πft)ey of frequency f=30GHz and amplitude H0=1000Oe in the region 0≤x≤2nm. The data were fitted using Eq. (23) with β=0.02 and α=0.01.