Ferromagnetic Pd Research Articles

Energy bands of and spinwave dispersion in Pd 3Fe

The results of a band calculation carried out for ferromagnetic Pd 3Fe suggest that the anisotropy observed in the spinwave dispersion curves may be explained by the particular shapes of the upspin and downspin Fermi surfaces and the symmetries of the corresponding one-electron states. The specific number of outer electrons per unit cell seems important in producing a Fermi level in a trough in the density of states so that only few states are involved. Qualitative considerations along the same lines seem capable of explaining differences in the spinwave dispersion of Pt 3Mn compared with that of Pd 3Fe.

Muon spin relaxation in ferromagneticPdMn

Positive-muon (μ +) spin relaxation experiments have been carried out in the dilute ferromagnetic alloy Pd+2 at.% Mn (T c=5.8 K). In the paramagnetic state the inhomogeneousμ + linewidth is proportional to the bulk magnetization. BelowT c theμ + linewidth and the width of theμ + local field distribution in zero applied field are both in qualitative accord with the Sherrington-Kirkpatrick theory of disordered magnets.

Percolation concentration and saturation of the Pd moment in ferromagnetic Pd alloys

In PdFe, PdCo, PdNi, PdMn or PdGd alloy systems long-range ferromagnetic order always sets in whenever the concentration of magnetic units is about 0.11 at.%, irrespective of the type of solute or the total magnetic moment of the magnetic unit, the latter being a polarisation cloud seeded either by a single solute atom or by a statistically formed cluster of solute atoms. This observation, in conjunction with the facts (i) that in PdGd the d band polarisation is negative in zero or weak external fields with (ii) that for all the weakly ferromagnetic alloys the ferromagnetic Curie temperature, TC, is proportional to the solute concentration, c, is interpreted to mean that the spatial extent of the polarisation cloud cannot be as large as is currently assumed and that the onset of ferromagnetic order is through a percolation process involving ferromagnetic correlations between the otherwise isolated or independent magnetic units, rather than through any direct overlap of such units. Also, in appropriate cases, the concentration dependence of the bulk magnetisation, mu b, is approximately as predicted by the Landau theory of phase transitions for the weakly ferromagnetic alloys whereas for higher solute concentrations mu b is proportional to Tc, ironically a characteristic of very weak itinerant ferromagnetism. The average moment on a Pd atom, mu Pd, increases linearly with Tc up to Tc approximately=340K, above which temperature it assumes a constant value equal to the maximum possible Pd moment. This abrupt saturation of the Pd moment, indicative of some sort of phase transition, is discussed in relation to the theoretically predicted metamagnetic transition in Pd and more generally to the concept of a characteristic temperature for an exchange-enhanced but non-magnetic transition metal.

The extraordinary hall effect in dilute Pd based alloys

Abstract The extraordinary Hall effect has been measured for ferromagnetic alloys Pd Ni, Pd Co, Pd Fe and Mn . In the low concentration region, different behaviour of Pd Ni and Pd Co in comparison with Pd Fe and Pd Mn confirms the existence of local orbital moments of Ni and Co in Pd.

μ + studies of conduction electron polarization in Pd and dilute [formula omitted] Fe alloy

The Knight shift of interstitial μ + in Pd was found to be −0.040 (2)% at 300 K, corresponding to 4.5 times larger hyperfine field per atomic moment compared to μ + in Ni. Using this value, the RKKY oscillation in the region outside the giant moment was found to explain the observed larger broadening in spin-glass Pd Fe (0.015 at.%) compared to ferromagnetic Pd Fe (0.28 at.%).

Spin-wave dispersion relation in Pd 3Fe at 4.2 K

The spin-wave dispersion relation of ferromagnetic Pd 3Fe at 4.2 K has been measured by neutron inelastic scattering methods. At large wavevectors the dispersion relation is very anisotropic and there is evidence in the [00ζ] and [ζζ0] directions of intrinsic spin-wave broadening effects.

NMR Study in PdCo and PdNiCo Alloys

NMR of Co 59 has been performed in ferromagnetic PdCo alloys. The internal field changes from -215 kOe in pure Co metal to 230±5 kOe in alloys of Co diluted in Pd. The results are consistent with the previous measurements by nuclear polarization and Mössbauer effect experiments. The line width is very broad in alloys with low Co concentration. Even in 0.5% Co alloy, the width still has the value of 50 MHz. T 2 shows rapid decrease with decreasing Co concentration. The experiment has also been performed on Co 59 in ferromagnetic Pd x Ni 1- x Co system. The results are quite similar to those in PdCo alloys.

Magnetic hyperfine structure of 125Te in ferromagnetic Pd 2MnSb

A large internal magnetic field of +857 ± 9 kOe has been observed at 125Te in ferromagnetic Pd 2MnSb (4.2 K). This gives a precise measure of the nuclear g factor ratio g e/ g 0 = −0.2270 ± 0.0015.

Hyperfine field at A, C and D site antimony in Pd2MnSb

We have observed in ferromagnetic Pd 2 MnSb, a strong nuclear resonance from Sb at regular sites (D sites) and a weak resonance from Sb occupying Pd sites (A and C sites), with hyperfine fields of 638 kOe and 523 kOe respectively at 4.2°K. Resonance lines are also observed from D site Sb presumably having slightly different surroundings.

Negative magnetoresistance in dilute ferromagnetic alloys

A model recently proposed by Long and Turner to explain the low temperature electrical resistivity of dilute, ferromagnetic Pd based transition metal alloys, is extended to include the effect of an applied magnetic field. A second order expression is derived for the temperature and field dependent resistivity of such alloys at temperatures well below the Curie temperature. Using recent zero field measurements on dilute Pd Fe alloys evaluate certain parameters, numerical estimates are then made of the ‘impurity’ magnetoresistance.

Giant Moments in Pd(Ni) Alloys near the Critical Composition

Neutron-scattering experiments show evidence of long-range magnetic polarization of the palladium matrix in dilute ferromagnetic Pd(Ni) alloys. The measured cross sections, for alloys containing up to 4.7 at.% nickel, are interpreted in terms of a model in which the concentration of ferromagnetically aligned giant moments is less than the concentration of nickel atoms.

Analysis of the specific heat cusp of two dilute ferromagnetic Pd - Mn alloys

The specific heat in the vicinity of T c of two dilute Pd-Mn alloys is analysed. The critical behaviour of a 1.35 at.% Mn alloy ( T c =4.477° K) is characterised by the exponents α - = −1.36 ± 0.12 and α + = −0.20 ± ±0.06 below and above T c, respectively. Therefore the specific heat appears to be non-divergent.

Magnetic Moment Distribution in Dilute Alloys of Nickel in Palladium

Measurements have been made at 4.2°K of the elastic diffuse scattering of 4.8 Å neutrons from ferromagnetic Pd(Ni) alloys containing 3.0, 3.4, 4.7, and 6.3 at.% Ni. The magnetic cross sections, measured with scattering vectors ranging from 0.17 to 1.1 Å−1, are all strongly peaked towards the forward direction. The range of polarization of the palladium matrix around a nickel atom deduced from the measurements is independent of nickel concentration up to 4.7 at.% Ni, and is larger than that obtained by Holden and Low1 for dilute Pd(Fe) and Pd(Co) alloys. The cross section per nickel atom extrapolated to the forward direction increases with increasing nickel concentration up to 4.7 at.% Ni, and then drops sharply. For the most dilute alloys the extrapolated forward cross sections are about a factor of 2 less than those calculated from a general expression due to Marshall and Balcar,2 and it is concluded that the effective concentration of aligned polarization distributions is less than the true concentration of nickel atoms. The mean moment of the nickel atom and the matrix polarization per nickel atom were calculated from the measured cross sections and are independent of concentration for the three most dilute alloys, with values of 0.9±0.2 μB and 3.7±1.4 μB respectively.

Internal field at the 119Sn site in the Heusler alloy Pd 2MnSn

The internal field at the 119Sn site in ferromagnetic Pd 2MnSn has been determined by Mössbauer effect and its sign has been found to be negative. The origin of the field has been discussed.