Spin fluctuations of isolated Fe impurities in Pd-based dilute alloys: effect of ferromagnetic host spin polarization

Abstract

The magnetic moment and spin fluctuation temperature TSF of isolated Fe atoms in a number of Pd-based binary alloys, namely Pd0.95M0.05 (M = Ni, Rh, Mo, Ag, Cd, In, Sn, Th and U), have been determined from the local susceptibility χloc(T) of 54Fe probe nuclei measured by means of the time differential perturbed angular distribution (TDPAD) technique. Depending on the element M added to the Pd matrix, the results derived from Curie–Weiss analysis, χloc(T) = C/(T+TSF), reveal strong enhancement or suppression of the ferromagnetic host spin polarization Sh associated with the giant moment of Fe. Concurrent with the variation in host spin polarization, we have observed a large change in the spin fluctuation temperature TSF, showing an exponential rise with diminishing value of Sh. The results, analysed on the basis of the Kondo model, indicate that spin fluctuations caused by the antiferromagnetic interaction associated with the negative conduction electron spin polarization are suppressed progressively by an incremental addition of a positive contribution to the effective exchange interaction.

Lattice Size Induced Moment Formation on Isolated Fe Atoms in Nanocrystalline Nb

“…The resulting ferromagnetic interaction between Fe-d and the nn Nb moment can effectively decrease the Kondo coupling J and thus reduce T K . The calculations presented above support our proposition that positive host spin polarization can diminish T K substantially, as has been observed in many bulk alloys [3,19]. They are also consistent with our earlier results [8] in nano-Cu, though an enhanced antiferromagnetic s À d interaction increases the T K in nano-Ag, as expected.…”

Ferromagnetic Kondo Effect at Nanocontacts

“…As NRG shows, only through addition to the bare Anderson model of a direct intersite ferromagnetic exchange coupling between the magnetic impurity and the leads a permanent impurity spin can be stabilized. In this case the regular (antiferromagnetic) Kondo effect and the associated screening with formation of a spin singlet is turned over to a ferromagnetic Kondo effect, with antiscreening and formation of a fully rotationally invariant, integer or half integer spin S. This role of direct impurity-lead ferromagnetic exchange, consistent with the impurity spin dynamics measured by perturbed γ-ray distribution in bulk alloys [12,13], could be crucial at nanocontacts in nearly ferromagnetic metals, where spectroscopic signatures of the ferromagnetic Kondo effect may be observable in I-V conductance anomalies.…”

“…A way to stabilize a permanent moment and to overwhelm the effective antiferromagnetic electron-impurity coupling just found by NRG is to add an explicit ferromagnetic coupling between the impurity and the conduction electrons. Experimental evidence of the important role of such a direct ferromagnetic exchange has repeatedly been claimed [12,13]. Physically, the electron-impurity ferromagnetic exchange must be substantial since the host metal is nearly ferromagnetic and the impurity wavefunction, much like that of a hostmetal atom, extends well over neighboring sites.…”

Quantum phase transition and Fermi liquid behavior inPd1−xNixnanoalloys

“…Isolated magnetic 3d impurities like Mn, Fe, and Co produce strong ferromagnetic spin polarization of the Pd d electrons [2][3][4][5][6], This polarization extends over several atomic lengths around the impurity and results in giant moments. Thus, even an extremely small amount (<0.1%) of these impurities produces a long-range ferromagnetic order [7], When the impurity is Ni, however, it merely increases the enhanced susceptibility of Pd further, up to a relatively high impurity concentration xc ~ 2.6%.…”