Iron phthalocyanines (FePc) adsorbed onto a Ag(110) substrate self-assemble into different monolayer phases going from rectangular to different oblique phases, with increasing molecular density. We ...have investigated the oxygen uptake capability of the different phases and their associated magneto-structural changes. Our study combines scanning tunneling microscopy and spectroscopy (STM/STS), X-ray magnetic circular dichroism (XMCD), and density functional theory (DFT) calculations. STM measurements reveal that the oxygenation reaction of the FePc/Ag(110) generally involves a displacement and a rotation of the molecules, which affects the electronic state of the Fe centers. The oxygen intercalation between FePc and the substrate is greatly obstructed by the steric hindrance in the high-density phases, to the point that a fraction of oblique phase molecules cannot change their position after oxidizing. Depending on the oxidation state and adsoption geometry, the STS spectra show clear differences in the Fe local density of states, which are mirrored in the XAS and XMCD experiments. Particularly, XMCD spectra of the oxidized phases reflect the distribution of FePc species (nonoxygenated, oxygenated-rotated, and oxygenated-unrotated) in the different cases. Sum rule analysis yields the effective spin (m s eff) and orbital (m L) magnetic moments of Fe in the different FePc species. Upon oxygenation, the magnetic moment of FePc molecules increases about an order of magnitude, reaching m TOT ∼ 2.2 μB per Fe atom.
The crossover from antidot to dot magnetic behavior on arrays patterned in a ferromagnetic thin film has been achieved by modifying only the geometry. A series of antidot arrays has been fabricated ...on cobalt with fixed diameter d and by reducing the period of the array p from p >> d to p < d. A dramatic change in the coercivity dependence with p, correlated with a significant modification in the magnetic domain structure observed by x-ray photoemission electron microscopy, evidences the crossover. An intermediate regime has been found between the superdomain structure present in antidot arrays and the array of astroid-state noncorrelated dots. The study has been reproduced for a different ferromagnetic material, permalloy, and supported by micromagnetic simulations.
Permalloy antidot thin films were grown by sputtering onto anodic alumina templates, replicating their hexagonal order inside micrometrie geometric domains. The advanced high-spatial and sensitive ...x-ray photoemission electron microscopy technique under an applied magnetic field has enabled magnetic domain structure imaging and quantitative hysteresis loop analysis inside nanoscale regions with geometric order and at border regions. The study has been complemented by vibrating sample magnetometry and magneto-optic Kerr effect measurements. The magnetization process is clearly determined by the geometry characteristics of the antidot arrays. Inside geometric ordered domains, the strength of effective in-plane magnetic anisotropy depends on the antidot diameter-to-film thickness ratio, which determines the partial balance between stray fields generated by magnetic charges at the lateral surface of the antidots and those at the upper- bottom film surface. In addition, the border regions between geometric domains act as pinning centers for magnetization reversal and eventually generate a harder magnetic region.
Parimagnetism in HoCo2 and TmCo2 Bonilla, C M; Herrero-Albillos, J; Figueroa, A I ...
Journal of physics. Condensed matter,
04/2014, Letnik:
26, Številka:
15
Journal Article
Recenzirano
X-ray magnetic circular dichroism (XMCD), longitudinal (χac) and transverse (TS) ac magnetic susceptibility have been measured in the RCo2 series (R = Ho, and Tm) as a function of temperature and ...applied magnetic field. We show that parimagnetism is a general behavior among the RCo2 ferrimagnetic series (R being a heavy rare-earth ion). XMCD results supply evidence of the presence of two compensation temperatures above Tc, defining two different parimagnetic configurations, which is a fully unexpected result. The inverse χ'ac curve exhibits a small anomaly which vanishes under low applied magnetic fields. The combination of TS and XMCD measurements allows one to depict new magnetic phase diagrams for these compounds of the RCo2 series. A new scenario allowing one to understand the observed phenomenology as a Griffiths phase-like behavior is proposed, where the amorphous RCo2 represents the undiluted system case.
Imaging magnetic responses of nanomagnets by XPEEM Sandig, O.; Herrero-Albillos, J.; Römer, F.M. ...
Journal of electron spectroscopy and related phenomena,
October 2012, 2012-10-00, 20121001, Letnik:
185, Številka:
10
Journal Article
Recenzirano
Odprti dostop
► PEEM sample holder with magnetic field and temperature control. ► Magnetic fields up to 50mT during imaging. ► Magnetic hysteresis of an individual Fe nanocube at 115K. ► Imaging the local magnetic ...susceptibility χAC as a function of temperature.
The Spin-resolved Photoelectron Emission Microscope (SPEEM) is a permanently installed set-up at Helmholtz-Zentrum Berlin (HZB). Due to its specific contrast it is mainly used for magnetic imaging and micro-spectroscopy with quantitative analysis. A crucial point in magnetic imaging is the application of magnetic fields. Many experiments require observation of magnetic responses or the preparation of a certain magnetic state during the measurement. We present a dedicated magnetic sample holder combining magnetic field during imaging with additional temperature control. This set-up enables SPEEM to measure magnetization curves of individual Fe nanocubes (18nm)3 in size. If additionally alternating magnetic fields are applied we can image the local magnetic AC susceptibility (χAC) as a function of temperature. The latter is ideally suited to visualize local variations of the Curie temperature (TC) in nano- and microstructures.
Strips containing arrays of submicrometric triangular antidots with a 2D square periodicity have been fabricated by electron beam lithography. A clear ratchet effect of 180° domain wall motion under ...a varying applied field parallel to the walls has been observed. The direction is determined by the direction of the triangle vertices. In contrast, no ratchet effect is observed when the antidot array is constituted by symmetric rhomb-shaped antidots.
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