Showing papers by "Albert Fert published in 1979"

Magnetic and transport properties of nickel-rare earth amorphous alloys

Abstract: The authors have studied the inter-related magnetic and transport properties of several amorphous Ni3RE alloys prepared by sputtering. The resistivity and magnetoresistance measurements reveal new aspects of the influence of the amorphous structure on the transport properties: in particular an increase of resistivity on magnetic ordering and an associated positive magnetoresistance. They analyse the magnetic and transport properties in the random anisotropy model and evaluate the crystal field acting on the rare earth moments.

Magnetoresistance of silver single crystals containing rare-earth impurities

Abstract: We present magnetoresistance measurements on single crystals of silver containing Tb or Dy impurities together with the analysis of the contributions from quadrupole and exchange scattering.

Transport properties of amorphous rare-earth alloys

Abstract: We discuss several aspects of the transport properties of RE amorphous alloys : contributions from magnetic ordering to the resistivity, magnetoresistance and its anisotropy, low temperature resistivity anomalies, extraordinary Hall effect. The transport properties of rare-earth (RE) amorphous alloys only begin to be studied. Some interesting effects have been observed : resistivity minima related to magnetic ordering and characteristic magnetoresistance, resistivity minima of non-magnetic origin in other systems, magnetic contributions to the Hall effect.. . Theoretical models have been proposed but not yet completely tested. We will present the topic in its present raw state. 1. Resistivity and magnetoresistivity of magnetic RE alloys. 1 . 1 EXPERIMENTAL RESULTS ON Ni,RE AMORPHOUS ALLOYS [I, 21. Figure 1 shows the Fig. 1. Resistivity of amorphous Ni,Dy versus temperature in several fields [I, 21. resistivity of a Ni,Dy alloy as a function of the temperature. There is a minimum at T, -15 K while the ordering temperature is about 10 K [2]. The change of resistivity between 1.2 K and the minimum is 1.1 %. Similar minima are observed in Ni3Ho and Ni3Er but the resistivity changes are smaller as the RE spin decreases suggesting an exchange scattering effect. The magnetoresistance (figures 1 and 2) confirms the magnetic origin of the resistivity minimum. There is a positive magnetoresistance at low temperature with a peak in dpldH near the ordering temperature. Well above this temperature the magnetoresistance becomes progressively weaker and takes approxi( T 8)2 where B is close to mately a dependence in the Curie-Weiss tempe>ature 6f the paramagnetic susceptibility. The low temperature upturn of p and the positive magnetoresistance can be ascribed to the same mechanism : a positive contribution from Fig. 2. Magnetoresistance of amorphous Ni,Dy versus temperature at several fields [2] (Ap, = 5 Apll + ApL). Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1979584 C5-226 R. ASOMOZA, I. A. CAMPBELL AND A. FERT magnetic ordering to p. The sign of the resistivity the same between first, second and third neighbours : change with increasing magnetic order is however ( JRo. JR ) = ,uF J2 where pl is a parameter of local opposite to what is normally observed in crystalline magnetic order. From eq. (1) and (3) one derives : allow. The Ni3Dy, Ni3Ho and Ni3Er behaviours are J similar with only decreasing amplitudes as the RE Pm = ~ + 1 pM(C1 + C: { a l l@ k,) 1 1 ~ 3 (4) spin decreases. Ni3Gd shows a somewhat different behaviour on which we shall come back in section 1.3. Non-magnetic and magnetic Ni-Y alloys show resistivity minima which have a much smaller amplitude and are field independent (see section 2). Such nonmagnetic effects may exist in Ni3Dy, Ni3Ho or Ni3Er but are certainly covered up by the magnetic contributions. 1 .2 RESISTIVITY FROM COHERENT EXCHANGE SCATTERING IN AMORPHOUS ALLOYS. The interference between waves scattered by the exchange interaction on neighbour magnetic ions contributes to the resistivity if there is some correlation between the spin directions. This so-called coherent-exchange scattering contribution has been calculated by de Gennes and Friedel [3] for crystalline ferromagnets. This calculation has been recently extended by Fert et al. [l, 21 to the case of amorphous alloys. Fert et al. [2] find the following expression of the resistivity due to exchange scattering :