Charge induced Variation of the Magnetization in Nanoporous Ni-Pd
- PDF / 447,593 Bytes
- 6 Pages / 595 x 842 pts (A4) Page_size
- 25 Downloads / 227 Views
R2.6.1
Charge induced Variation of the Magnetization in Nanoporous Ni-Pd Christian Lemier1, Sadhan Ghosh1, R. N. Viswanath1, Guang-Tao Fei1,3, Jörg Weissmüller1,2 1
Institut für Nanotechnologie, Forschungszentrum Karlsruhe, Karlsruhe, Germany Fachrichtung Technische Physik, Universität des Saarlandes, Saarbrücken, Germany 3 Institute of Solid State Physics, Chinese Academy of Sciences, Hefei, P. R. China 2
ABSTRACT Changes in the electronic structure in superficial space-charge regions may substantially affect the properties of metals near their surface. In materials with a nanoscale porosity and with a high surface to volume ratio, changes in the properties of even a thin surface layer may have a noticeable effect on the properties of the entire material. In nanoporous metals immersed in an electrolyte, the space charge can be induced as a part of the electric double layer at the metal-electrolyte interface. Here we present first experiments on the effect of surface charging in a nanoporous metal on the magnetism. We report reversible changes in the magnetic moment in Ni-Pd alloys. As possible origins of the dependency of the magnetization on the surface charge density we discuss band filling and, alternatively, magnetostriction. X-ray diffraction and dilatometry reveal a considerable strain amplitude, about of 6×10-4, resulting from surface charging; this corresponds to a surface-induced pressure in the crystal lattice, in the order of 0.3 GPa. INTRODUCTION Many materials properties of metals, such as conductivity and magnetization, depend on the electronic structure. Consequently it can be expected that by charging a metal surface, the band occupancy and, with it, the properties can be tuned reversibly in a superficial layer [1]. It is well known that a considerable amount of charge can be accumulated in space-charge regions at metal-electrolyte interfaces; due to the efficient screening in metals (the Thomas-Fermi screening length is less than 1 Å [2]) the charge is localized essentially in the outermost atomic layer. In nanoporous materials, due to the large surface to volume ratio, the superficial region occupies a substantial part of the volume even though only a very thin layer is involved. Thus, such materials with their large surface to volume ratios open the way for experimental observation of effects due to surface charging. Recently, it has been shown, that in a nanoporous material immersed in an electrolyte, the change in surface bonding accompanying surface charging can induce a pressure change in the crystallites and, thereby, lattice strains in the order of 1×10-3 [3]. It is of interest to verify experimentally that these processes can also affect other properties. Here, we present results of a study aimed at investigating the changes in magnetic properties of nanoporous metals as a function of an applied potential in an electrolyte. As the material of our study we selected Pd1-xNix alloys, since high surface area powders of the alloy can be conveniently prepared by the inert gas condensation tec
Data Loading...
