G. M. Kalvius

Precision measurement of the electric quadrupole interaction in zinc metal

To decide on the validity of various values for the quadrupole coupling constant of Zn metal available in the literature, we have used the frequency modulation technique to the 93.3 keV Mössbauer resonance of67Zn. We obtained for a67Zn metal absorber: e2qQ/h =vO = 12.34 ± 0.03 MHz. The asymmetry parameter was found to be η=0.00−0+0.06. These precise values can be used as a calibration standard for67Zn Doppler drives.

High-pressure Mössbauer study of hyperfine interactions in magnetically ordered europium chalcogenides: EuO, EuS, EuTe

Abstract The effect of pressure on the isomer shift S and the magnetic hyperfine field B was investigated in the divalent europium chalcogenides at 4.2 K by means of the 21.6 ke V Mossbauer resonance of 151 Eu. The variation of the lattice parameter with pressure causes a quite different change in hyperfine interactions than the one observed upon varying the anion within the chalcogenide series. In EuTe no change in the magnetic ordering behaviour has been observed up to 57 kbar.

Mössbauer determination of the E2/M1 mixing ratio of the 77 keV transition in197Au and of the sign of the electric field gradient in KAu(CN)2

A Mössbauer measurement of the E2/M1 mixing ratio of the 77 KeV transition in197Au yielded δ=−0.352±0.005. With this result, Mössbauer absorption spectra of KAu(CN)2 single crystals show that the electric field gradient at197Au in this compound is negative. This implies that the field gradient is mainly produced by 6pz electrons. The data also indicate a large vibrational anisotropy of Au in KAu(CN)2.

Magnetic order in NpO2 and UO2 studied by muon spin rotation

Abstract Muon spin rotation/relaxation (μSR) measurements were carried out in zero applied field on NpO 2 and UO 2 above and below their transition temperatures of 25 and 30.8 K, respectively. In NpO 2 , a spontaneous spin precession pattern is observed for T 2 where the 30.8 K transition is well established as the Neel temperature for antiferromagnetic order. The μSR patterns are, in their basic features, quite alike for the two compounds. This establishes unambiguously that the transition at 25 K in NpO 2 is basically of magnetic origin. The ordered moment on Np is estimated to be smaller than about 0.15 μ B , i.e. less than 10% of the moment on U in antiferromagnetic UO 2 .

Mössbauer study of electronic relaxation in crystalline and amorphous DyAg

Abstract The 161 Dy Mossbauer spectra of crystalline and amorphous DyAg were measured between 300 and 4.2 K. The amorphous sample was prepared by sputtering. At low temperatures typical magnetic relaxation spectra are observed in both materials. The main difference is the presence of a smeared out lattice electric field gradient and the slowing down of the relaxation rate in amorphous DyAg. Both effects are caused by a random local distortion of the cubic symmetry of the DyAg lattice by the amorphization process.

Knight shifts and relaxation in gadolinium above the curie temperature

We have studied the transverse μSR signal in Gd metal in the temperature region 1–2 TC, and it is demonstrated that measurements in the paramagnetic range can be used to obtain the hyperfine field at the muon site, as well as to give information on the fluctuations of the Gd spins. The critical exponent for slowing down of Gd spin fluctuations is 0.56(5) above 1.05 TC but decreases to 0.15(5) below 1.05 TC. Comparisons with results from PAC and Mössbauer measurements are discussed.

Spin dynamics and freezing in magnetic rare-earth quasicrystals

Abstract Muon spin relaxation measurements of RE 8 Mg 42 Zn 50 (RE = Gd, Tb) quasicrystals have revealed slower spin dynamics and more prompt spin freezing for Tb than Gd, due to “crystalline electric field” splitting in low rare-earth site symmetry. Inhomogeneous spin freezing leads to a low-temperature state with local field distribution characteristic of a concentrated disordered magnet.

A μSR Study of Magnetic Correlations in CeNiSn

The formation of magnetic correlations in CeNiSn has been studied by muon spin rotation and relaxation (μSR) spectroscopy covering the temperature range from 250 K to 33 mK. Mainly a single crystalline sample was used. At high temperatures (≥ 2 K) a behaviour similar to that of a spin fluctuator like UAl2 is observed, meaning that over the whole temperature range the paramagnetic moments fluctuate extremely fast (≥ 31014 Hz). Below 1 K the material exhibits properties typical for a paramagnet moving towards magnetic order, but no transition into long-range order could be observed down to the lowest measured temperature. The dependences of muon spin relaxation rate and muon spin precession frequency on external field (applied parallel to the a-axis) are unusual and indicate the formation of extended spin correlations up to short-range order.

Mössbauer spectroscopy with actinide elements

Although formally equivalent to the lanthanide (4f) elements, the light actinides show a much more varied behaviour due to the larger spatial extent and ionizability of the 5f electrons. The application of Mössbauer spectroscopy for the determination of electronic properties of the actinides is outlined. Emphasis is put on high pressure Mössbauer experiments using the 60 keV transition in237Np to study questions of delocalization of 5f electrons.

Effect of high pressure on the electric field gradients at two inequivalent lattice sites of tantalum in

The pressure variation of the electric field gradients at substitutional tantalum atoms on the two lattice sites (A and B) of ω-zirconium have been determined to be (∂ lnqA/∂P)T = −1.05(26)10−3 kbar−1 and (∂ lnqB/∂P)T = +6.03(40)10−3 kbar−1. In addition the thermal expansion coefficients of the unit cell of ω-Zr were found to be α‖ = +3.5(3)10−6 K−6 and α⊥ = +7.9(4)10−6 K−1. A combined analysis of the pressure dependence and the previously determined temperature dependence of the electric field gradients supports the assumption of two different bonding types at the A and B sites.