Induced long-range magnetic interactions in Pd single crystals covered with ferromagnetic Ni are observed in perturbed angular correlation measurements applying monolayer-resolved sample preparation. The 100 Pd͞ 100 Rh probes sense magnetic interactions even seven atomic layers away from the Ni-Pd interface. The results are interpreted assuming fluctuations of magnetic moments strongly interacting with the 100 Rh nuclei. [S0031-9007(96) PACS numbers: 75.30. Hx, 75.70.Cn, 76.80.+y The range of the magnetic polarization in the strongly exchange enhanced metal Pd in contact with Ni was investigated in a pioneering magnetometry experiment as early as 1984 [1]. As the most probable interpretation, the authors attributed the additional magnetic moment to Pd, although they could not decide from the bare experimental results whether it is actually located in Ni or Pd. Meanwhile, the existence of ferromagnetic polarization in magnetic-layer systems with only a few monolayers (ML) Pd deposited on ferromagnetic substrates (Fe, Co, Ni) is experimentally well established and theoretically treated [2]. The lattice parameters of such ultrathin Pd layers differ from the bulk value as a consequence of epitaxial growth. This can influence the magnetic properties considerably [2,3]. When the surface of Pd with bulk lattice parameters, e.g., of a single crystal, is covered with a film of a ferromagnetic material (Fe, Co, Ni), neither the nature (static or fluctuating moments) nor the range of induced magnetic interactions are well known from experiments, since such a system is hardly accessible to many conventional experimental methods. Ab initio theoretical treatments of such systems are available, however [4].The present experiment offers a new approach for range measurements of induced magnetic spin polarization in Pd. The further aim is to determine the nature of the polarization in Pd with minimized disturbance of the lattice parameters. Ideally, the only wanted disturbance is the magnetic influence by the ferromagnetic coverage; we have chosen isoelectric Ni. For a quantitative range measurement preferentially a monolayer-resolving method has to be applied. For this purpose the perturbed angular correlation (PAC) method with radioactive 111 Cd probe nuclei has recently been introduced [5]. We have selected 100 Pd decaying to 100 Rh as probe nuclei. The clean preparation and controlled deposition of radioactive 100 Pd probe atoms on Pd surfaces (avoiding other contaminations) were achieved within the present experiment [6]. Thus another transition-element probe (besides the Mössbauer probe 57 Fe) is available for microscopic investigations of magnetic multilayer systems. 100 Pd͞ 100 Rh as a PAC probe is of special importance, because it can be used as an extremely diluted impurity as well as a self atom. This opens the field for local investigations of surfaces and interfaces of 4d elements or of composite 3d͞4d-element multilayers.In short the experiment is described as follows: 100 Pd atoms (10 23 10 24 of a ML) were de...

The local susceptibilities and the 3d spin dynamics of isolated nickel ions in various alkali-metal hosts have been measured, utilizing the method of perturbed /-ray distribution after recoil implantation. In the heavy alkali-metal hosts Cs, Rb, and K, the local susceptibilities of the isolated Ni ions show the temperature behavior of a fully localized spin-orbit-coupled 3d 9 configuration. Clear host dependence of the magnetic behavior is seen in the spin-fluctuation rates which increase with decreasing host volume. In Na, the magnetic behavior drastically deviates from that of the purely ionic configuration, and Ni ions in Li as well as in Ca and Ba hosts are nonmagnetic.PACS numbers: 75.20.Hr, 75.30.Hx, 76.30.Fc, 76.80.+y In recent years the question of localization of electrons in the partially filled shells of transition metals has again become a subject of considerable interest. Following the table of transition elements by Smith and Kmetko, ! the degree of localization is the discriminating parameter for many bulk properties. The magnetism of most 4/ metals is known to be determined by localized electrons, whereas many d elements are strongly influenced by band structure and hybridization effects. Marking the change between localized and itinerant d and / electrons, the intermediate region, comprising, e.g., Ce and Fe, and Co and Ni, is rendered prominent by an extreme complexity of all-important bulk quantities.In the field of dilute magnetic alloys, the search for local moments is guided by the idea that magnetic moments will develop if the interaction of electrons "inside" one impurity atom survives hybridization or crystal fields. As nickel is estimated to have the strongest spinorbit coupling and exchange interaction in the 3d series, 2,3 a well-defined local magnetic moment might be expected in some metallic hosts, yet no such observation has been published.So the question arises whether nickel impurities will develop a fully localized configuration when incorporated in extreme environments. One such extreme system, which is characterized by sharp contrasts in atomic volume, electronegativity, and density of states between the constituents, has already been studied, Fe impurities in the alkali metals Cs, Rb, and K. 4 Here the isolated iron impurities are divalent and exhibit an unperturbed spin-orbit-coupled 3d 6 configuration. Another question of interest is the actual ionic configuration of the Ni ions in the host. Estimates on the basis of a Born-Haber cycle 5 suggest that Ni might be monovalent in the alkali metals and, even more interesting, might display charge fluctuations.In many metallic hosts Ni impurities show nonmagnetic behavior; in NiPd alloys, however, a positive magnetic hyperfine field has been found. 6 " 9 . This has been explained by negative core and positive orbital contributions and, in addition, transferred fields from neighbor-ing Pd atoms, but it is not an indication of an unperturbed well-defined moment. For Fe impurities, local orbital moments are thought to be typical f...

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Measurements of the temperature dependence of the chemical shift at Fe nuclei in FeS2 (pyrite) and Fe impurities in RuS2 (laurite) were performed on high-purity synthetic single-crystal samples using the perturbed-angular-distribution method. Equivalent, considerably negative, and temperature-independent chemical shifts were observed in both hosts, which we attribute to strong van Vleck paramagnetism.Bulk susceptibility data at low temperatures show no local moment formation at Fe sites due to nonstoichiometric sulfur content. The results are evaluated with respect to the photoactive properties of these materials and the requirements for solar-energy applications.