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The spatial and temporal correlations of magnetic moments in the paramagnetic regime of ${(\mathrm{Mn},\mathrm{Fe})}_{2}(\mathrm{P},\mathrm{Si})$ have been investigated by means of polarized neutron diffraction and muon-spin relaxation techniques. Short-range magnetic correlations are present at temperatures far above the ferromagnetic transition temperature $({T}_{C})$. This leads to deviations of paramagnetic susceptibility from Curie-Weiss behavior. These short-range magnetic correlations extend in space, slow down with decreasing temperature, and finally develop into long-range magnetic order at ${T}_{C}$.

New inelastic neutron scattering data for ErFe2Si2 and Tm 169 Mossbauer spectra for TmFe2Si2 are presented. These data are analysed in terms of the crystal field acting at the rare earth site and new crystal field parameters are presented. The new crystal field parameters are compared with previous parameters to show the systematics associated with a change in transition metal.

The hexagonal TmCuAl is studied with magnetic specific heat, resistivity and Tm 169 Mossbauer spectroscopy measurements. TmCuAl orders antiferromagnetically at T N = 1.9 K. The distance between the two levels of the quasi-doublet ground state of TmCuAl, determined with the Tm 169 Mossbauer pseudo-quadrupole shift, amounts to 2.8(3) K. Based on the temperature dependence of the Tm 169 quadrupole splitting a provisional calculation has been made for the crystal field diagram with a coupling constant α , which is non zero.

We show that, in rare earth based insulators, measurement of the thermal dependence of the muon spin-lattice relaxation rate at high temperature provides information on the nature of the magnetic correlations and on the crystal-field energy splitting, if any.

We first discuss magnetic excitation and relaxation processes which have already been recognized experimentally by muon spin relaxation experiments. Our examples are taken from experiments performed on strongly correlated electronic systems, magnetic metals and geometrically frustrated magnetic compounds. In another part, focusing on the flux-line lattice in the Bragg-glass phase of superconductors, we show that a muon spin experiment can provide information on the in-plane correlation length of the lattice.

The electronic spin transition in [Fe(btr)(2)(NCS)(2)] . H2O (btr = 4,4'-bis-1,2,4-triazole) is probed by longitudinal field muon spin relaxation measurements. The muSR spectra could be analyzed with two different components, corresponding to two muon sites. For both components, an increase in magnetic fluctuations is observed at the LS --> HS transition, i.e. crossing the spin transition temperature coming from low temperature, if a sufficiently high field is applied. Even below the transition temperature, magnetic fluctuations are still found. For one of the two union sites, muonium formation is clearly found below the spin-crossover temperature. (C) 2004 Elsevier B.V. All rights reserved.

Host–guest interactions of ferrocene in KY zeolite were investigated using muon spin relaxation (μSR). Temperature-dependent measurements enable us the determination of the activation parameters for the low energy dynamic processes of the encapsulated ferrocene. A comparison between the μSR results and the earlier neutron measurements illustrates the advantage of the former technique for probing the lowest unoccupied molecular orbital (LUMO).

Gd 2 BaCuO 5 is studied with 57 Fe Mossbauer spectroscopy on a 57 Fe (1/2%) doped sample and with muon spin relaxation on an undoped sample. Cu–Cu and Gd–Gd magnetic order are found to occur simultaneously at T N =11.8 K. The Mossbauer results suggest a first-order magnetic transition for the Cu sub-lattice.

We report the first μSR measurements done on a cluster of monodisperse Pd nanoparticles. The measurements give access to the dipole field from the unpaired electron magnetic moments. We find for a two shell compound that the field is smaller than expected. The moments at the origin of the field are quasi-static, i.e. fluctuate in the microsecond time range.

We have probed the low temperature spin dynamics in two pyrochlore lattice compounds R2Ti2O7, where the rare earth (R3+) form a sublattice of tetrahedra linked by their corners such that geometrically derived magnetic frustration is possible. In Yb2Ti2O7 (Yb3+: S′=1/2, XY anisotropy), we show that below 0.24 K , the temperature of the known specific heat λ transition, there is no long range order. The transition, in fact, corresponds to a first-order change in the fluctuation rate of the Yb3+ spins. Above the transition temperature, the rate is in the GHz range and it follows a thermal excitation law, whereas below the transition, the rate is in the MHz range and it is temperature independent. In Gd2Ti2O7, where the S-state Gd3+ ions are antiferromagnetically coupled, there is a magnetic phase transition near 1 K . As the temperature is lowered through the critical region, λZ, the spin-lattice relaxation increases. On lowering the temperature to 21 mK , λZ tends to a temperature independent value. Concomitant with the persisting electronic spin fluctuations, we observe oscillating components evidencing long-range spin correlations. Therefore, temperature independent spin dynamics is observed even after passing through a magnetic phase transition and even when the magnetic correlations are long range.

WepresentaneutronpowderdiffractionstudyonTmCuAl,crystallizingintheZrNiAl-typehexagonalstructure.OurdataconfirmmagneticorderingbelowT c ¼ 1:9K.Themagneticstructureisalongitudinalspinwavedescribedbyapropagationvectork ¼ð 12 0qÞ withTmmagneticmomentsalongthec-axis.Inadditiontothat,acommensurateantiferromagneticcomponentwithinthebasalplanewithk ¼ð 12 02Þ developsbelowthemagneticphasetransitionatT 1 D1:2K. It leads to a rather complex magnetic structure below T 1 : One-third of the thulium moments has aconsiderablyreducedmagnitudecomparedtotheremainingones.Nofurtherphasetransitionswereobserveddownto50mK.r 2002ElsevierScienceB.V.Allrightsreserved. PACS: 75.25.+z;75.30. m;61.12.LdKeywords: Magneticstructures;Neutrondiffraction;Rare-earthintermetallics 1. IntroductionTheternaryRCuAl(R=rareearth)compoundscrystallize,exceptforLaCuAl,intheZrNiAl-typehexagonal structure (space group P-62m). Pre-viousstudiesrevealedaferromagneticorderingforthe compounds containing the heavy rare-earth(Gd–Er)[1,2].Onthecontrary,anantiferromag-neticbehaviorwasfoundinCeCuAl[3],PrCuAland NdCuAl [4]. The magnetic properties ofTmCuAlremainunclear.Nomagneticorderdownto 1.8K was found in Ref. [1], while magneticordering below 1.9K and a possible additionalphase transition at lower temperatures are re-ported in Refs. [5,6]. The negative Curie–Weissconstantandamaximuminthemagneticsuscept-ibilitysuggesttheimportanceofantiferromagneticinteractions in this compound. The

In GdNi5, the muon localizes at the 3f interstitial site and below ∼80 K a second muon site becomes populated, either at the 6m or 6k site. These latter sites are located in a ring surrounding the (0, 0, 1 2 ) site and the muon occupies all six sites within the time range of the experiment (10−9 s). This ring site is metastable and the muon hops to the preferred 3f site. We determine the mean time of stay of the muon in the ring site and show that it is governed by a multi-phonon quantum diffusion process. The coincidence energy is measured to be Ea=272 (10) K and the tunneling matrix element J=0.11 (2) meV.

We have studied DyFe4Ge2 and ErFe4Ge2 with 57Fe, 161Dy and 166Er Mossbauer spectroscopy. DyFe4Ge2 has a c axis anisotropy, whereas ErFe4Ge2 could be interpreted with two subspectra with both an angle with respect to the c axis. In ErFe4Ge2 a magnetic phase transition is observed at T=8 K.

In GdNi5, the muon localizes at the 3f interstitial site and below ∼80K a second muon site becomes populated, the so-called 6ring site. This ring site is metastable and the muon hops to the 3f site. We determine the mean time of stay of the muon in the ring site and show that it is governed by a multi-phonon quantum diffusion process. The coincidence energy is measured to be E a =272(10)K and the tunneling matrix element J=0.11(2)meV.

The polycrystalline compound EuBa 1.3 Pr 0.7 Cu 3 O 7− δ has been prepared and investigated by the means of 141 Pr Mossbauer spectroscopy. The observed 141 Pr Mossbauer isomer shift, δ (at T =4.2 K)=0.10 (15) mm/s relative to PrF 3 , reflect a valence state of 3+ for Pr located at the Ba site in EuBa 1.3 Pr 0.7 Cu 3 O 7− δ . Magnetic order of the Pr sublattice was not observed at T =4.2 K in contrast with the compound Eu 0.3 Pr 0.7 Ba 2 Cu 3 O 7− δ where magnetic order of the Pr sublattice appears at T =12 K. Our results explain why Pr behaves very similar to other 3+ cations (La, Nd) when substituted for Ba in this system, and suggests that suppression of superconductivity by Pr substituted at the rare earth site is a consequence of the hole filling effect.

C. T. Kaiser, V. W. J. Verhoeven, P. C. M. Gubbens, F. M. Mulder, I. de Schepper, A. Yaouanc, P. Dalmas de Reotier, S. P. Cottrell, E. M. Kelder, and J. Schoonman Interfacultair Reactor Instituut, Delft University of Technology, 2629 JB Delft, The Netherlands Departement de Recherche Fondamentale sur la Matiere Condensee, Commissariat a l’Energie Atomique, F-38054 Grenoble Cedex 9, France ISIS Facility, Rutherford Appleton Laboratory, Chilton, Didcot, OX11 0QX, United Kingdom Laboratory of Applied Inorganic Chemistry, Delft University of Technology, 2628 BL Delft, The Netherlands ~Received 15 March 2000!

We report on zero- and longitudinal-field muon spin depolarization measurements performed on single crystals of the Kondo insulator CeNiSn. The initial muon beam polarization is parallel to the a crystal axis. Going down in temperature, we observe in zero field a monotonous increase of the exponential damping rate starting at ∼20 K . In longitudinal field measurements the damping rate drops to zero at a few mT, reflecting a quasi-static field distribution at the muon site. Contrary to previously published results, our data do not allow to safely determine whether the observed increase of depolarization at low temperature originates from the electronic–magnetic correlations or from nuclear magnetic moments of the compound.

The magnetic ordering and crystal field interactions of the Pnma phases of both Tm2BaCoO5 and Tm2BaNiO5 are investigated by 169Tm Mossbauer spectroscopy and the temperature-dependent hyperfine interactions are compared with those obtained elsewhere for Tm2BaCuO5. The Pnma phases are shown to order magnetically at temperatures of 3.5(2) K (Tm2BaCoO5) and 4.85(5) K (Tm2BaNiO5), the order being induced by the transition metal. For Tm2BaNiO5 an additional first-order transition observed at T≤1.4 K is identified with the independent magnetic order of the thulium sub-lattice.

We report zero-, longitudinal-, and transverse-field positive muon spin relaxation ({mu}SR) measurements in single crystals of the heavy-fermion superconductor UBe{sub 13} [T{sub c}=0.83(2) K]. Our zero-field measurements provide an upper limit for any quasistatic magnetic moments in this system below 100 K of 0.001{mu}{sub B}, consistent with previous measurements on polycrystals. From the transverse-field measurements we find a lower bound for the London penetration depth {lambda}{sub L}=1210 nm. This value implies a lower limit for the effective mass consistent with the low-temperature specific heat. (c) 2000 The American Physical Society.

We summarize our recent μSR results on the magnetic and superconducting properties of the heavy-fermion superconductor UPt3. Whereas zero-field measurements show no signature of the superconducting and magnetic phase transitions, the experiments in high transverse field evidence the presence of two inequivalent magnetic regions for temperatures ranging from 0.2 to 115 K with an anomaly near the magnetic transition. From low transverse field experiments in the low-temperature superconducting phase (B phase), we deduce the temperature dependence of the superfluid densities. We briefly discuss all these results in relation to those obtained for other compounds of this family.

GdNi 5 is a simple metallic ferrimagnet with well understood magnetic properties. It has been used in the past as a testing ground for validating muon spin relaxation theories. Here we report on the muon diffusion and site localization in its paramagnetic phase, i.e., above 30.85 K. The muon localizes at the interstitial 3f sites over the whole temperature range. Below ∼70 K the interstitial 6m sites become populated as well. These sites form a ring surrounding the (0,0, 1 2 ) site and the muon can occupy all these sites within its lifetime. Above 40 K the muon residing time in these sites is relatively short and it jumps to the 3f site by a quantum diffusion process.

Positive muon spectroscopy (μSR) and 170Yb Mossbauer absorption measurements have been performed in the cubic Kondo insulator YbB12 down to the 50 mK temperature range. We observe a paramagnetic fluctuation mode at low temperature, with a weak moment amplitude ( ≈ 10−2 μB) and a slow fluctuation frequency ( ≈ 60 MHz) which remains constant between 0.04 K and 4.2 K. No indication of a magnetic phase transition is found down to 0.04 K.

We present a quantitative analysis of the temperature dependence of the muon spin relaxation rate measured in simple magnets. We consider the low temperature, critical and high temperature regimes.

We report muon spin rotation measurements of the temperature dependence and anisotropy of the magnetic field penetration lengths in the heavy fermion superconductor . We observe a strong axial anisotropy. At 0.05 K we obtain for the penetration length parallel and perpendicular to the c axis (150) A and (130) A, respectively. at low temperatures excludes a superconducting order parameter in the B phase with only a line of nodes in the equatorial plane of the Fermi surface. The combined analysis of and measured in the B phase favours an hybrid order parameter with point nodes at the poles and a line of nodes at the equatorial plane. The A phase is characterized by a larger density of nodes than the B phase.

A combined Tm Mossbauer spectroscopy and mSR ~muon spin rotation! study is presented on a polycrystalline sample of TmNi2B2C. The first experimental technique shows the coexistence of two types of Tm 4 f magnetism at 0.3 K, one related to a magnetic Tm moment of 4.3(1)mB and the other to a small Tm moment of ;0.1mB . This second type of magnetism is suggested to be caused by carbon vacancies present in TmNi2B2C. These C vacancies locally modify the crystalline electric field and therefore the Tm 4 f magnetism. Since these vacancies are ideal cavities in which muons can reside, it is suggested that mSR only probes this ;0.1mB magnetism. @S0163-1829~98!05217-5#

Specific heat and muon spin rotation and relaxation data are presented for two geometrically frustrated systems: Gd2Ti2O7 which antiferromagnetically orders and Yb2Ti2O7 which presents dynamical short range correlations at low temperature. The muon data help to characterize the spin dynamics of these two compounds.

In the hexagonal compound CsNiBr 3 the μ SR spin–lattice relaxation rate increases notably as the sample is cooled down towards T N 1 , a conventional signature of the slowing down of the magnetic fluctuations. This is in contrast with earlier NMR measurements for which no critical magnetic fluctuations were observed. Zero-field spectra, recorded in the magnetically ordered phase exhibit Bessel-like oscillations. However, this does not allow to conclude for the incommensurability of the magnetic structures in the two magnetic phases of CsNiBr 3 . The damping of the oscillations, only found below the second phase transition T N 2 , is a signature for the rotation of the canted spins around the c-axis.

In Li 0.6 TiO 2 the longitudinal muon spin relaxation function has been measured for temperatures between 10 and 600 K. The μSR spectra were analyzed with a Markov process for multiple collisions. The time scale found for the Li + diffusion is of the order of the microsecond or shorter. Above T = 100 K the magnetic field distribution at the muon is decreasing with increasing temperature.

Zero-field muon spin rotation experiments provide evidence for an antiferromagnetic component in the magnetic structure of the intermetallics ZrZn2., 5 pages, 2 figures

The magnetic properties of PrRu${}_{2}$Si${}_{2}$ have been investigated experimentally by specific heat, single-crystal magnetization, ${}^{141}$Pr M\"ossbauer and muon spectroscopies, neutron powder diffraction, and inelastic neutron scattering, leading to the determination of its zero-field phase diagram and its crystal electric-field energy levels below 40 meV. PrRu${}_{2}$Si${}_{2}$ undergoes a magnetic phase transition at ${T}_{N}$ $\ensuremath{\simeq}$ 16 K to an axial incommensurate sine-wave magnetic structure characterized by a wave vector $\ensuremath{\tau}$ = (0.133, 0.133, 0), followed by a first-order phase transition at ${T}_{C}$ $\ensuremath{\simeq}$ 14.0 K to an axial ferromagnetic structure. The lowest crystal electric-field states are the two singlets $|{\ensuremath{\Gamma}}_{t1}^{(1)}〉$ and $|{\ensuremath{\Gamma}}_{t2}〉$ separated by 2.25 meV. The low-temperature properties are described by a Hamiltonian identical to that of an Ising system with a transverse magnetic field. Since the ratio of the exchange energy to the energy splitting between the singlets is sufficiently large, it exhibits spontaneous magnetization. The nature of the two singlet states explains the giant magnetic anisotropy. The random-phase approximation predicts the value of the high-field magnetization but yields a low-field magnetization too small by $\ensuremath{\sim}$ 15$%$. Possible application of our results to uranium intermetallic compounds is pointed out.

The technique of 197Au Mossbauer absorption spectroscopy has been used to study four varieties of the high nuclearity gold molecular cluster compounds abbreviated as Au55, all having a cuboctahedral structure, with 12 PPh3-ligands or modifications of PPh3. The technique of emission spectroscopy developed in our laboratory [1] has been applied to four different molecular platinum carbonyl cluster compounds of varying cluster nuclearity, abbreviated as Pt38, Pt26, Pt24, and Pt19 [2]. The four Au55 compounds were studied, both as dry materials and as frozen solutions. The M6ssbauer parameters of the chlorine ligated site of the water soluble version differ strongly due to the effect of Na+ on the Au-Cl distances. In the frozen solution, the effect of the ionic charge on this cluster can be clearly seen. The similarity of the spectra of all the Pt compounds, especially the occurrence of a substantial singlet contribution in all spectra, is explained by a coalescing mechanism for the low-nuclearity clusters, induced by the neutron irradiation damage inflicted while preparing the sample as M6ssbauer sources. The observed decrease of the absorption intensity with increasing temperature is evidence for a cluster character of the sample remaining after neutron irradiation.

From magnetic, specific heat, 170Yb Mossbauer effect, neutron diffraction, and muon spin relaxation measurements on polycrystalline Yb2Sn2O7, we show that below the first order transition at 0.15 K all of the Yb3+ ions are long-range magnetically ordered and each has a moment of 1.1?B which lies at ?10° to a common fourfold cubic axis. The four sublattice moments have four different directions away from this axis and are therefore noncoplanar. We term this arrangement splayed ferromagnetism. This ground state has a dynamical component with a fluctuation rate in the megahertz range. The net ferromagnetic exchange interaction has an anisotropy that favors the local threefold axis. We discuss our results in terms of the phase diagram proposed by Savary and Balents [ Phys. Rev. Lett. 108 037202 (2012)] for a pyrochlore lattice of Kramers 1/2 effective spins.

The magnetic properties of Tm${\mathrm{Ni}}_{2}$${\mathrm{B}}_{2}$C were measured with $^{169}\mathrm{Tm}$ M\"ossbauer spectroscopy at temperatures from 0.3 to 700 K. A clear transition in the quadrupole splitting (QS) near 1 K is observed, which might be due to magnetic ordering or to quadrupole ordering. Although a possible small magnetic Tm moment of \ensuremath{\sim}0.1(1)${\mathrm{\ensuremath{\mu}}}_{\mathit{B}}$ is found below \ensuremath{\sim}1 K, the change in QS is larger than expected due to magnetic ordering only. Therefore the nature of the transition is unclear at this moment. From the temperature dependence of QS is deduced that the crystal-field ground-state level most likely equals the singlet $a|\ensuremath{-}4〉+b|0〉+a|+4〉$.

The magnetic properties of the compound TmFeAl have been studied using57Fe and169Tm Mossbauer spectroscopy, magnetic measurements and neutron depolarization (ND). The compound exhibits a complex magnetic behaviour. At 4 K it contains a Tm moment of 7μB and a distribution of Fe moments with an average of 0.5μB. Between 10 and 60 K a distribution in magnetic ordering temperatures is observed. ND displays the growth of small magnetic domains when the temperature decreases towards 4 K. The structural disorder of the Fe atoms in the lattice combined with the competing exchange interactions between the different types of atoms and the high anisotropy of the Tm moment gives rise to the observed magnetic behaviour. Results of high field magnetization and57Fe Mossbauer spectroscopy are presented also for GdFeAl and YFeAl.

We present a positive-muon spectroscopy study of the cubic Kondo lattice , where the crystal-field splittings of the ion amount to a few tens of K. The transition from the paramagnetic to the antiferromagnetic state is detected at . The zero-field data provide evidence of an unusual temperature dependence of the mean nuclear dipole field at the muon site. The longitudinal relaxation rate as well as the published quasi-elastic neutron linewidth, both recorded far into the paramagnetic region (, are analysed in detail. We show that the classical kf exchange interaction cannot explain the observed thermal variation of the dynamical and neutron widths. We perform a calculation of the 4f excitation spectra using the expansion, applied to the Anderson one-impurity Hamiltonian in the non-crossing approximation (NCA), in the presence of crystal-field splittings, and compare the results with the observed thermal variations of the dynamical widths. Whereas the NCA reasonably explains the neutron measurements, it strongly overestimates the low-temperature width. We discuss different possible reasons for this discrepancy.

Muon-spin-relaxation experiments and ac low-field magnetization measurements have been carried out on the superconductor Ce${\mathrm{Ru}}_{2}$. The relaxation rate of the muon-spin polarization in zero field exhibits a small but significant increase below ${T}_{M}\ensuremath{\simeq}40$ K, which is suppressed by applying a longitudinal field. This result taken together with magnetization measurements provides definite evidence for the occurrence of static electronic magnetism involving extremely small magnetic moments. Our work shows that Ce${\mathrm{Ru}}_{2}$ is a member of a restricted family of superconducting compounds that order magnetically with extremely small magnetic moments at a temperature much higher than that at which they become superconducting.

The 141 Pr Mossbauer isomer shift and hyperfine field of PrBa 2 Cu 3 O 7 and some other praseodymium oxides were measured. When we put the isomer shift of these oxides on a linear scale, we find for PrBa 2 Cu 3 O 7 the mean valency 3.4(1). This value corresponds to the number of holes which goes into the Pr-2(Cu(2)-O 2 ) layers. The spectra below T N ≈ 17 K are broadened, but no well resolved hyperfine field split pattern is observed. We surmise that these spectra are due to relaxation. In the discussion we ascribe the different results on the valency of Pr in PrBa 2 Cu 3 O 7 reported in the literature to a different use of the term valency. A model is furthermore proposed in which we suggest that the correlation of the Pr4f shell introduced into the O 2p wave functions is responsible for the anomalous properties of PrBa 2 Cu 3 O 7

Four types of molecular Au 55 clusters, with different types of ligands, have been studied using 197 Au Mossbauer spectroscopy. Emission Mossbauer measurements were also performed on the larger Pt309 cluster, in which 197 Au was produced by neutron activation. There is a large influence of the ligands on the charge densities at the surface atoms of the metal atom cluster cores. For the Au 55 clusters, the inner core atoms have a different charge density at the nucleus than the bulk metal, and it depends also slightly on the type of ligands on it. For the Pt 309 compound, the inner core atoms have the same charge density at the nucleus as in the corresponding bulk metal. We, therefore, conclude that the inner core of the Pt 309 cluster is metallic with respect to the electronic charge densities, while this is not yet the case for the Au 55 cluster.

We present zero-field muon-spin-relaxation data on the ferromagnetic fluctuations near the Curie temperature of the intermetallic GdNi5, which is a Heisenberg magnet with strong dipolar interaction. Our data show that the critical longitudinal ~along the wave vector qO spin fluctuations above and below the Curie temperature are similar. They are an experimental proof of this similarity. This result is explained using the dynamical scaling theory of Halperin and Hohenberg. Although the transition from the paramagnetic to the ordered state of a simple ferromagnet is an archetypical second-order phase transition, the dramatic effect of the dipolar interaction on the nature of the critical paramagnetic spin fluctuations has been fully understood only recently. An almost quantitative agreement has been achieved between the experimental data from magnetization, 1 neutron, 2 and local probe 3,4 techniques and mode coupling theory. 5 In contrasts below the Curie temperature TC the experimental data are scarce 6,7 and a complete theory is still lacking. 8 This report presents a detailed study on crystals of the spin dynamics for a dipolar Heisenberg ferromagnet by a local

In this survey, an overview will be given about lanthanide intermetallics studied with rare earth Mossbauer spectroscopy. Results of Pr, Gd, Dy, Er, Tm and Yb compounds will be presented and compared with the emphasis on Pr and Tm results. Crystal field and magnetic interaction and relaxation will be treated to describe the physical behaviour of rare earth compounds.

We have studied by zero-field and longitudinal fieldμSR measurements the uniaxial antiferromagnetic intermetallicsNdRh2Si2. The measurements have been performed on single crystals. Our data show that the magnetic field at the muon site is parallel to thec axis. Below the Neel temperatureTN the spin-lattice relaxation is driven by a two magnon process. In the paramagnetic region nearTN we observe, a critical divergence of the damping rate.

The current integrating technique has been implemented using a CdWO4 scintillator mounted onto a 28 × 28 mm2 PIN photodiode. With this method we were able to measure count rates an order of magnitude higher than commonly used in Mossbauer spectroscopy, and down to count rates as low as 500000 per second. Very small 141Pr Mossbauer resonance absorption effects could at 4.2 K be detected (≈10−4), some of them amongst the smallest ever to be recorded. As an example we show the 141Pr Mossbauer spectrum of PrCu2Si2 at 4.2 K.

We have studied byμSR spectroscopy the intermetallicsUTr 2Si2 where Tr=Co, Rh or Pt. Whereas for the Co compound we only get information on the muon localisation site, from the other two materials we obtain information on their electronic properties. We compare the characteristics of theirμSR response.

141Pr Mossbauer spectroscopy has been realized with use of the current integrating technique. As an example, we show the141Pr Mossbauer spectrum of PrCu2Si2 at 4.2 K.

The141Pr Mossbauer isomer shift and hyperfine field spectrum of PrBa2Cu3O7−y were measured at 25 and 4.2 K, respectively. The isomer shift corresponds to an intermediate valency of 3.4(1) and the hyperfine field spectrum at 4.2 K seems to indicate a hyperfine field of 29(3) T.

We have recorded at ISIS zero field and longitudinalμSR relaxation spectra on a single crystal of the Van- Vleck paramagnetPrNi 5 from room temperature down to 0.09K. Our data clearly indicate that at low temperature the rare earth spin dynamics is quasi-static, i.e. its correlation time is larger than 10−6 s. From theμSR methodological point of view, this work provides the first example of aμSR study of the dynamics of an hyperfine-enhanced nuclear dipole system.

We report zero field and longitudinal fieldμSR measurements on single crystals of the ferromagnet PrRu2Si2 (Tc≃15K). BetweenT=Tc and 250K we observe a quasi-static spin dynamics of the Pr3+ ion sub-lattice. BelowTc, depending on the orientation of the initial muon beam polarisation relative to thec axis of the compound, we find either an oscillating signal or an exponential depolarisation function. These latter data allow us to get information related to the muon in PrRu2Si2.