G. de Doncker

Arguments from external field measurements in favour of a spin-density-wave component in the magnetism of α-Mn

Abstract In order to illustrate the different nature of the magnetism underlying the two magnetic hyperfine fields in α-Mn, we present measurements in applied magnetic fields and at various temperatures. It was concluded that one hyperfine field is due to a local-moment antiferromagnetism and the other exhibits features related to the existence of a spin density wave (SDW).

External-field influence on the magnetic hyperfine fields in alpha-manganese

We report a study on the magnetic nature of the two hyperfine fields observed in α-Mn by PAC. Both of the field sites behave completely differently under the influence of an external field ranging from zero to 4 Tesla. The so-called high field originates from the local moment antiferromagnetism of the matrix, while the low field should be associated with an itinerant magnetism.

Indium-impurity interactions in a nickel host

The electric field gradients created at 111Cd nuclei by dilute Al, V and Cr impurities in the nickel matrix are studied by the technique of time-differential perturbed angular correlation. The results show conclusively that there exists a strong repulsive interaction between the In probe and the Al, V or Cr impurity atoms. The magnetic hyperfine field satellites due to various probe-impurity configurations originate from a highly non-random distribution of impurities within a 78-atom sphere (five atomic shells in a FCC lattice) around the In probe.

Hyperfine interaction in Ni79Mn21 and Ni76Mn24

We report on PAC measurements revealing very different magnetic behaviour in two nearby alloys. The Ni79Mn21 alloy orders at TC=280(5) K, but a two field sites interpretation is needed. Both hyperfine fields (hff) are in the ratio 1∶2 and their distributions have the same absolute width, the relative abundance of the high field site is 30%. A slope change in the hff (T) curve at low temperature may indicate the transition into the mixed state. In the Ni76Mn24 alloy we observe magnetic ordering at T=95(3) K followed by a smooth increase of the effective hff upon cooling but with an anomalous minimum around T=20 K.

Impact of baf2 detectors on nuclear solid-state investigations

High resolution time differential angular correlation, now achievable at low cost by the fast and efficient BaF2 detectors, will be introduced from some examples recently worked out. The results obtained manifest a new impetus for this technique in its extended application to particular problems in nuclear solid state research.

Satellite hyperfine fields in low concentration NiMn alloys

Concentration- and temperature dependent measurements were made on NiMn-alloys with the perturbed angular correlation technique (PAC). At room-temperature, samples of 1.3; 2.4; 3.6; 5.6; 6.9 and 8.3 at%Mn were examined. Field values on both sides of the Ni-value were observed with a pronounced concentration dependence above 3 at%Mn. The 3.6 at%Mn-sample was examined as function of temperature between 284 K and 573 K. Each of the fields has the same temperature-behaviour, resulting in the same Curie-temperature, which is however smaller than the Curie-temperature for pure Ni.

Magnetic hyperfine field and electric field gradient for111Cd at the Kr/Fe interface

Polycrystalline iron foils implanted to high Kr doses were doped with111In and the magnetic hyperfine field as well as the electric field gradient measured. From the present TDPAC experiments we observed a substantial fraction of probes in a “defect” site, with its hyperfine parameters Δ|Bhf|=6.9% and Vzz=1.12 1017V/cm2, in close similarity with those expected for the Kr/Fe interface.

Hyperfine interaction measurements inMnSi-alloys

PAC-experiments were performed on111Cd in Mn1−xSix (x=8.8at%) alloys. The high-field site (h) due to the local moments existing at site II positions is almost unaffected by the Si-impurities. For the second field site (1), supposed to be due to SDW, the ordering temperature is shifted to 77(2)K, although the field value is very similar to the pure α-Mn value. This observation supports our earlier interpretation of the magnetism in pure α-Mn.

Residual impurity effects on the magnetic ordering in α-Mn observed by hyperfine interaction

We report on the lattice location of indium in and the magnetic ordering of manganese in its α- and β-phases, as seen by perturbed angular correlation. Quadrupole interaction spectra show that indium prefers to replace Mn atoms of type I in α-Mn, but replaces type II atoms in the β-Mn structure. The interaction strength equalseQVzz/h=3.6 (6) MHz in α-Mn and 172.3 (3) MHz with ν=0.13 (1) in β-Mn. No magnetic ordering down to 4.2 K was observed in β-Mn, while belowTN=95 K in the α-Mn phase, a magnetic hyperfine interaction appears indicating two distinct magnetic probe environments. The hyperfine field, when measured atT=4.2 K, equals for 70% of the probes 6.33 (1) T, while the remaining fraction senses a 3.10 (4) T field. The magnitudes of the hyperfine fields are essentially unaffected by a variety of conditions in the sample preparation. The ordering temperature, on the contrary, turns out to be rather sensitive to residual impurities especially any oxygen contamination.

Third neighbour hyperfine field shift in a diluteNiAl alloy

In the binary Ni98.5Al1.5 alloy we observed well resolved satellite hyperfine fields at111Cd nuclear probes. The hyperfine shifts derivated are −4.0(3); −8.5(3) and ⃛14.0(3)% relative to the pure nickel value. From the relative intensity of the four components as well as from the quadrupole interaction data we identify the satellites as impurity-probe configurations containing zero, one, two or three Al impurities in the third neighbour shell only. The third neighbour contribution to the hyperfine field at Cd in nickel equals ΔH3= +4.5kG/μB-atom, allowing an estimate ΔH1≃ −17.8 kG/μB-atom for the first shell contribution, confirmed by a similar experiment on Ni98.5Pd1.5.