Tuning the Dzyaloshinskii-Moriya Interaction in Pt/Co/MgO heterostructures through MgO thickness

The interfacial Dzyaloshinskii-Moriya interaction (DMI) in the ferromagnetic/heavy metal ultra-thin film structures , has attracted a lot of attention thanks to its capability to stabilize Neel-type domain walls (DWs) and magnetic skyrmions for the realization of non-volatile memory and logic devices. In this study, we demonstrate that magnetic properties in perpendicularly magnetized Ta/Pt/Co/MgO/Pt heterostructures, such as magnetization and DMI, can be significantly influenced through both the MgO and the Co ultrathin film thickness. By using a field-driven creep regime domain expansion technique, we find that non-monotonic tendencies of DMI field appear when changing the thickness of MgO and the MgO thickness corresponding to the largest DMI field varies as a function of the Co thicknesses. We interpret this efficient control of DMI as subtle changes of both Pt/Co and Co/MgO interfaces, which provide a method to investigate ultra-thin structures design to achieve skyrmion electronics.Comment: 18 pages, 11 figure

Demographic strategies of a dominant tree species in response to logging in a degraded subtropical forest in Southeast China

International audienceAbstractKey messageThe demography of pioneer tree species (Pinus massonianaLamb.) is significantly affected by logging in Southeast China. Logging negatively affects the population growth rate ofP. massoniana, which facilitates the growth of individual trees but has no effect on reproduction probability. The survival and growth of seedlings contribute the most to population growth.ContextSubtropical forest degradation caused by unreasonable disturbances is closely related to anthropogenic activities in Southeast China, and the frequent small-scale logging activity by local people was the dominated disturbance regime in forests in this region over the past several decades.AimsThe objective of this study is to evaluate the demographic consequences of logging on Pinus massoniana, a pioneer tree species, at individual level (survival, growth, and fecundity) and population level (the population growth rate and size distribution) over short-term period.MethodsThe size of tree individuals was combined with vital rates using various modeling approaches based on demographic data from three annual censuses. The integral projection model (IPM) was constructed and used to conduct comparative demographic analyses.ResultsLogging negatively affected the population growth rate: from a slight expansion before logging to a moderate decline after logging. This study found a significant reduction in seedling recruitment after logging, and plant growth and mortality were slightly enhanced. The survival of seedlings greatly contributes to population growth rate compared to other life stages for both periods (before and after logging) while its relative importance decreases after logging. Seedling growth is also important to population growth, and its relative importance increased after logging. Shrinkage and fecundity have a minimal contribution effect on the population growth rate.ConclusionGrowing plants in a nursery with a similar demography to P. massoniana could be beneficial for pioneer species regeneration in that this will improve the survival rate and growth of small individuals after logging

Electrooxidation of Carbon Monoxide on Pd Thin Film-Coated Au Electrodes:Film Thickness Dependence

采用扫描循环伏安法及表面增强拉曼散射光谱研究了一氧化碳(CO)在钯修饰金电极上的吸附与氧化.结果表明CO氧化电位随钯膜厚度增加而正移,同时C—O伸缩振动频率红移.本文利用d能带理论解释观察现象.应力效应使CO吸附变强,难以氧化;但配体效应使CO吸附变弱,易于氧化.在薄膜中配体效应强于应力效应.The adsorption and electrooxidation of CO on Pd-coated Au electrodes were studied by cyclic voltammetry and surface-enhanced Raman spectroscopy (SERS) . It is found that CO oxidation activity is film thickness dependent. Cyclic voltammograms (CVs) showed that CO oxidation peak potential shifted positively with the increase of the Pd thickness. SERS showed a redshift of the C—O stretching frequency with increasing Pd film thickness. These observations were explained by the dband theory. The strain effect strengthens CO adsorption and stabilizes adsorbed CO,while the ligand effect weakens CO adsorption and eases its oxidation. The ligand effect overpowers the strain effect.作者联系地址：美国迈阿密大学化学与生化系;Author's Address: Department of Chemistry and Biochemistry,Miami University,Oxford,OH 45056,US

First-principles investigation of magnetocrystalline anisotropy oscillations in Co2FeAl/Ta heterostructures

We report first-principles investigations of magnetocrystalline anisotropy energy (MCAE) oscillations as a function of capping layer thickness in Heusler alloy Co2FeAl/Ta heterostructures. A substantial oscillation is observed in the FeAl-interface structure. According to k-space and band-decomposed charge-density analyses, this oscillation is mainly attributed to the Fermi-energy-vicinal quantum well states (QWSs) which are confined between the Co2FeAl/Ta interface and Ta/vacuum surface. The smaller oscillation magnitude in the Co-interface structure can be explained by the smooth potential transition at the interface. These findings clarify that MCAE in Co2FeAl/Ta is not a local property of the interface and that the quantum well effect plays a dominant role in MCAE oscillations of the heterostructures. This work presents the possibility of tuning MCAE by QWSs in capping layers and paves the way for artificially controlling magnetic anisotropy energy in magnetic tunnel junctions

Enhancing by Weakening: Electrooxidation of Methanol on Pt 3 Co and Pt Nanocubes This work was supported by the NSF (DMR-0731382 and CHM-0616436), S 3 IP, and Binghamton University.

No AbstractPeer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/78082/1/ange_201002888_sm_miscellaneous_information.pd