Beam-induced Fe nanopillars as tunable domain-wall pinning sites

Focused-electron-beam-induced deposition (FEBID) is employed to create freestanding magnetic nanostructures. By growing Fe nanopillars on top of a perpendicular magnetic domain wall (DW) conduit, pinning of the DWs is observed due to the stray fields emanating from the nanopillar. Furthermore, a different DW pinning behavior is observed between the up and down magnetic states of the pillar, allowing to deduce the switching fields of the pillar in a novel way. The implications of these results are two-fold: not only can 3-dimensional nano-objects be used to control DW motion in applications, it is also proposed that DW motion is a unique tool to probe the magnetic properties of nano-objects

Magnetic domain wall curvature induced by wire edge pinning

open14In this study, we report on the analysis of the magnetic domain wall (DW) curvature due to magnetic field induced motion in Ta/CoFeB/MgO and Pt/Co/Pt wires with perpendicular magnetic anisotropy. In wires of 20 mu m and 25 mu m, a large edge pinning potential produces the anchoring of the DW ends to the wire edges, which is evidenced as a significant curvature of the DW front as it propagates. As the driving magnetic field is increased, the curvature reduces as a result of the system moving away from the creep regime of DW motion, which implies a weaker dependence of the DW dynamics on the interaction between the DW and the wire edge defects. A simple model is derived to describe the dependence of the DW curvature on the driving magnetic field and allows us to extract the parameter sigma (E), which accounts for the strength of the edge pinning potential. The model describes well the systems with both weak and strong bulk pinning potentials like Ta/CoFeB/MgO and Pt/Co/Pt, respectively. This provides a means to quantify the effect of edge pinning induced DW curvature on magnetic DW dynamics.embargoed_20210815Herrera Diez, L.; Ummelen, F.; Jeudy, V.; Durin, G.; Lopez-Diaz, L.; Diaz-Pardo, R.; Casiraghi, A.; Agnus, G.; Bouville, D.; Langer, J.; Ocker, B.; Lavrijsen, R.; Swagten, H. J. M.; Ravelosona, D.Herrera Diez, L.; Ummelen, F.; Jeudy, V.; Durin, G.; Lopez-Diaz, L.; Diaz-Pardo, R.; Casiraghi, A.; Agnus, G.; Bouville, D.; Langer, J.; Ocker, B.; Lavrijsen, R.; Swagten, H. J. M.; Ravelosona, D

d-d exchange interaction in the diluted magnetic semiconductor Zn1-xCoxSe

The specific heat of the diluted magnetic superconductor Zn1-xCoxSe (x<0.05) has been measured in the temperature range 1.5<T<50 K and magnetic fields up to 3 T. The specific-heat data as well as susceptibility and magnetization data are well described by a model that takes into account the nearest-neighbor exchange interaction (JNN=-49.5 K) as well as a long-range interaction (JLR=-30/R6.3 K, where R is given in nearest-neighbor distance units). © 1992 The American Physical Society

Structural transitions of skyrmion lattices in synthetic antiferromagnets

Thin magnetic films with Dzyaloshinskii-Moriya interactions are known to host skyrmion crystals, which typically have a hexagonal lattice structure. We investigate skyrmion-lattice configurations in synthetic antiferromagnets, i.e., a bilayer of thin magnetic films that is coupled antiferromagnetically. By means of Monte Carlo simulations, we find that by tuning the interlayer coupling the skyrmion lattice structure can be tuned from square to hexagonal. We give a simple interpretation for the existence of this transition based on the fact that for synthetic antiferromagnetic coupling the skyrmions in different layers repel each other and form each others' dual lattice. Our findings may be useful to experimentally switch between two lattice configurations to, for example, modify spin-wave propagation

Ruderman-kittel-kasuya-yosida exchange interaction in many-valley IV-VI semimagnetic semiconductors

The Ruderman-Kittel-Kasuya-Yosida (RKKY) indirect-exchange interaction via free carriers is analyzed in the case of IV-VI semimagnetic semiconductors (diluted magnetic semiconductors). Carriers responsible for the RKKY interaction in these materials originate from the anisotropic band of heavy holes located at the point of the Brillouin zone (i.e., there are 12 equivalent valleys of this band). Both intervalley and intravalley electron processes contribute to the exchange coupling. Calculations of the RKKY exchange integral and the paramagnetic Curie temperature (FTHETA) are presented. The exchange integral is anisotropic, and its dependence on the interspin distance is significantly modified in such a way that the role of antiferromagnetic couplings is increased. As a consequence, the value of FTHETA is reduced

Magnetic properties of the diluted magnetic semiconductor Zn _1-xCr_xSe

The magnetic properties of a new diluted magnetic semiconductor Zn 1-xCrxSe are reported. Specific heat was measured for 1.5 K≤T≤20 K and B≤3 T, whereas magnetization data were taken at T=2 and 4.2 K for magnetic field (B≤6 T) along (100), (110), and (111) crystallographic directions. The data are interpreted using the crystal-field model for the Cr++ ion, including static Jahn-Teller distortion.</p

Structural transitions of skyrmion lattices in synthetic antiferromagnets

Thin magnetic films with Dzyaloshinskii-Moriya interactions are known to host skyrmion crystals, which typically have a hexagonal lattice structure. We investigate skyrmion-lattice configurations in synthetic antiferromagnets, i.e., a bilayer of thin magnetic films that is coupled antiferromagnetically. By means of Monte Carlo simulations, we find that by tuning the interlayer coupling the skyrmion lattice structure can be tuned from square to hexagonal. We give a simple interpretation for the existence of this transition based on the fact that for synthetic antiferromagnetic coupling the skyrmions in different layers repel each other and form each others' dual lattice. Our findings may be useful to experimentally switch between two lattice configurations to, for example, modify spin-wave propagation

Magnetic-resonance study of the diluted magnetic semiconductor Pb1-x-ySnyMnxTe

Electron paramagnetic resonance (EPR) was investigated in samples of the magnetically diluted semiconductor Pb1-x-ySnyMnxTe in the temperature range T=1.3 100 K. The samples had compositions in the range x=0.005 0.06,y=0.12 0.72 and carrier concentrations between p=1.6×1019 and 1.4×1021 cm-3. The temperature dependence of the EPR linewidth is strongly dependent on the carrier concentration. This can be understood within the framework of the Korringa relaxation mechanism and the two-valence-band model of magnetic properties of these crystals. For samples with high carrier concentrations (ferromagnetic at low temperatures) we obtained an s-d exchange integral of Jsd=33 2 meV. The role of metal vacancies in the effect of electron bottleneck of the EPR is also discussed