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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.

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.

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.

The hyperfine interaction is studied in two different crystal lografic forms of Mn. In the β-Mn no magnetic, but a distinct electric quadrupole interaction is found. Effects of heat treatment are discussed. For the α-Mn two magnetic field sites are found. Their temperature dependence and dependence on the In concentration are discussed.

A perturbed angular correlation study on Au85Fe15 in different metallurgical states and over a wide temperature range is reported. The hyperfine field and its temperature variation reflect a cluster glass behaviour due to chemical clusters of different sizes rather than a magnetic double transition.

The temperature and concentration dependence of the transferred hyperfine field in Au 1− x Fe x with 0.15 x 111 Cd probe shows a slope change at T / T c =0.25 for all concentrations below 20 at% Fe, but an almost continuous behaviour for higher concentrations. These results manifest a percolation-like magnetic behaviour but no magnetic double transition.

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.

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.

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.

Perturbed angular correlation spectroscopy was used to determine the magnetic hyperfine field at Cd impurities in PdFe alloys of nominal concentration 0.5, 1.5 and 3.5 at.% Fe. The mean hyperfine field follows the bulk magnetisation and shows a broad distribution with a minimum at 1.5 at.% Fe.

We introduce perturbed angular correlation (PAC) on radioactive isotopes as a new and feasible technique to sense the hyperfine field distribution in randomly disordered alloys. This technique is similar to μSR in the sense that it is a nuclear spin precession measurement, but more widely applicable in view of the limited instrumentation. We present our first results obtained using 111Cd as a typical PAC probe in Au–Fe alloys of different magnetic impurity concentration. Our data clearly show the onset of the spin glass freezing and allows one to derive the mean field value as a function of temperature as well as magnetic impurity concentration.

The temperature and concentration dependence of the hyperfine field in AuFe alloys in the concentration range of 15 to 28 at%Fe was measured by perturbed angular correlation (PAC) spectroscopy. The temperature dependence of the hyperfine field shows a slope change at T/TC = 0.25 for concentration below 20 at%Fe, while for higher concentration a continuous behaviour is seen.

For the alloy ${\mathrm{Au}}_{1\mathrm{\ensuremath{-}}\mathrm{x}}$${\mathrm{Fe}}_{\mathrm{x}}$ with 0.15lxl0.28, the magnetic ordering as a function of temperature was monitored by the magnetic hyperfine field at $^{111}\mathrm{Cd}$ probe nuclei. Using perturbed angular-correlation spectroscopy, we find a magnetically homogeneous behavior and for xl0.20 two distinct temperature regions (above and below T/${T}_{c}$=0.25). In addition two concentration regions are found, abruptly separating ferromagnetic ordering above ${x}_{c}$=0.202 from the cluster-glass region below. Our results support the interpretation of magnetic order in terms of a random iron distribution with the Fe coordination number as the critical factor.