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Ruthenium-doped yttrium gallium garnet single crystals were grown from a PbO/PbF2/B2O3 flux. Most samples are blue, occasionally green, orange or lemon yellow, depending upon the growth temperature and the amount of a divalent or tetravalent counterion. A spectroscopic study was carried out using several complementary techniques (optical absorption, MCD, and EPR). Low temperature MCD enabled discrimination among those absorption bands correlated to paramagnetic ions (Ru3+ or Ru5+) or diamagnetic Ru4+ at the octahedral site. Ru3+ dominates in the lemon yellow sample with a nominal Ge/Ru ratio of ≈7, whereas Ru5+ is responsible for the orange colour in a crystal with Ca/Ru ≈7. The strongest MCD features above 2.2 eV could be rationalised in terms of oxygen-to-Run+ (n = 3–5) charge transfer transitions in octahedral complexes, whereas the 2 eV band of blue crystals is tentatively assigned to an intervalence transition implying Ru4+. It is suggested that YIG films co-doped with ruthenium and a large amount of calcium or germanium might present interesting Faraday effect properties.

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.

We describe a method for measuring the local fields arising from the vortex lattice in YBa 2 Cu 3 O 7− δ which is based on the field dependence of the electro-nuclear energy levels of non-perturbing 170 Yb 3+ Mossbauer probes. From 4.2 K measurements of the second moment of the field distribution after a field-cooled (FC) treatment, we obtain the bulk penetration lengths ( λ ab ) for under-, optimum- and overdoped sintered samples and we estimate the evolution of the condensate density with doping. The overdoped samples were obtained by increasing the oxygen content or by adding 20% Ca. We find the presence of Ca increases the condensate density above the level obtained by adding oxygen to fill the chains and the condensate density of the planes increases at the same time that T c decreases. For an optimally doped grain-oriented sample of YBa 2 Cu 3 O 7− δ , we obtain the 4.2 K bulk penetration lengths ( λ ab and λ c ) and we also obtain estimates for the surface penetration lengths by measuring the induction appearing in the surface layers of the grains when fields below H c1 are applied after a zero-field cooling treatment. The surface penetration lengths are found to be not representative of the lengths obtained from within the bulk.

We report a 57 Fe Mossbauer study of superconducting samples of YBa 2 Cu 3 O 7 substituted with 1% Fe and also, in addition, up to 4% Co. Increasing the Co level has no influence on the 57 Fe quadrupole interactions but strongly increases the saturated 57 Fe hyperfine fields. For the sample with 4% Co, where the increased hyperfine field leads to a reduced interference between the magnetic subspectra, we carry out a quantitative analysis of the thermal dependence of the fluctuation rate of the 57 Fe hyperfine field. We compare the properties of the short-range correlated magnetic order introduced by the Co/Fe as sensed by the perturbing 57 Fe probe with those reported previously for the non-perturbing Mossbauer probe 170 Yb in the same system.

We investigated the annealing temperature, the carbon non-stoichiometry and the Fe doping effects on the physical properties of the superconductor HoNi 2 B 2 C 3 (1 ≤ × ≤ 1.35), using X-ray diffraction, magnetisation or electrical resistance measurements and 57 Fe Mossbauer spectroscopy. We show that the spontaneous re-entrant behaviour of HoNi 2 B 2 C which has been attributed to the occurrence of incommensurate magnetic states destructive to superconductivity, is strongly enhanced by quenching or by decreasing the annealing temperature. The re-entrant behaviour also increases with the carbon content and the 57 Fe (0.5 at.%) doping. We conclude that the chemical defects introduced by quenching, deviation from stoichiometry or Fe doping, depress superconductivity and favour the appearance of the re-entrant behaviour. Our 57 Fe Mossbauer investigation shows that the presence of the incommensurate magnetic orders in the re-entrant region does not lead to the introduction of a hyperfine field at the Fe probe.

The recent discovery of superconductivity (SC) in the quaternary borocarbide system Y–Ni–B–C has opened up a new area of research in SC. SC mainly occurs only for the end members of rare earths (R) and magnetism and SC coexist whenRis a magnetic ion (Ho, Er, Tm, and later in Dy). We will discuss and give some new results on the effects of annealing on the impurity phases and on low Fe doping rates on the coexistence between SC and magnetism in materials withR=Ho. Superconductivity has been reported in Y–Pd–B–C system with aTc(22 to 23 K) higher than the record for bulk intermetallics. The composition and structure of the SC phase(s) is still a topic of controversy that we will briefly discuss, giving new results.

We report lattice parameter and superconducting temperature transition ( T c ) measurements on ErNi 2 − x M 2− x B 2 C (M  Co, Pd, Pt), x = 0.20; M  Co, x = 0.05). We discuss the origin of T c lowering which is relatively modest for th substitutions Pd and Pt (d T c /d x ∼ − 12 K) and more pronounced for the non-isoelectronic substitution of Co (d T c /d x ∼ − 120 K). We also report 166 Er Mossbauer measurements for M = Co, x = 0.20 which evidence a main Er 3+ ordering temperature near 5 K and a saturated magnetic moment of 8μ B .

From 170Yb3+ Mossbauer measurements on Yb2Ni17 down to 0.05 K we have obtained the saturated 4f shell magnetic and quadrupole moments at the two Yb3+ sites. The combined influence of the Yb3+ crystal field and the Ni derived exchange interactions leaves an essentially pure fully stretched | J z = 7 2 〉 state at one site and a mixed state with a 40% reduction of the magnetic moment at the other site. The fully stretched state experiences a saturated molecular field of near 0.5 T. From the magnetisation measurements we obtain the magnetic ordering temperature of the Ni sublattice (145 K) and find that, in contrast to the other R2Ni17, the Yb3+ and Ni sublattice moments do not show a compensation temperature.

From measurements of the thermal dependence of 1/ T 1 the electronic fluctuation rate for the S′ = 1 2 ground state of 170 Yb 3+ Miossbauer probes in YBa 2 (Cu 1− x Zn x ) 3 O 7 , we find that the addition of Zn 2+ introduces a density of states at the Fermi level in the superconducting state. Gapless behaviour is reached when x reaches 0.06. We compare the information obtained from the 170 Yb 3+ probe when T c is reduced by adding Zn 2+ and/or by reducing the oxygen level.

The magnetic properties of the rhombohedral intermetallic compound Yb 3 Pd 4 have been investigated using 170 Yb Mossbauer spectroscopy and neutron diffraction. Magnetic ordering of the Yb 3+ moments sets in below T N =3.2 K, the saturated moment per Yb 3+ being μ s ⋍ 0.6μ B . The magnetic structure is antiferromagnetic and we discuss the possible moment orientations. In the paramagnetic phase, the thermal variation of the Yb 3+ 4f shell quadrupolar moment has been measured. cea.fr.

We have used 170Yb3+ Mossbauer spectroscopy on Yb3+ diluted at the rare-earth sites in Pr-xYxBa2Cu3O7 and in PrBa2Cu3O6 to examine the magnetic properties associated with the (hybridized) Pr3+ ions. Magnetic ordering in the non-superconducting compounds PrBa2Cu3O7 (T> = 16 K) and PrBa2Cu3O7 (T = 10 K) is identified by the appearance of a Pr3+-derive d molecular field and by a change in the Yb3+ paramagnetic relaxation rates. Evidence is presented suggesting the ordered Pr3+ magentic moments are aligned well away from the c-axis. The splitting of the three lowest crystal-field levels in PrBa2Cu3O6 is estimated to be about half that (∼ 50 K) in PrBa2Cu3O7. In the superconducting samples of Pr1-xYxBa2Cu3O7, the Yb3+ l ocal probes give evidence for an inhomogeneous behavior linked to statistical variations in the Pr3+/Y3+ occupancies. With increasing x, both the volume of the sample showing local Pr3+ magnetic order and the average ordering temperature decreases. There appears to be an anti-correlation between the superconducting transition temperature and the volume of the sample showing Pr3+ magnetic order, suggesting the local Pr3+ concentration needed to remove superconductivity (in favor of Cu (2)-based magnetic order) is near that needed to support local Pr3+ magnetic order.

We have used 170Yb Mossbauer spectroscopy on Yb3+ diluted at the Y3+ sites to study YBa2(Cu0.94Zn0.06)3Ox. In the fully oxygenated sample, the presence of Zn2+ introduces a Korringa dependence of the Yb3+ paramagnetic relaxation rate, indicating an increase in the density of states at the Fermi level, which is visible both above and below Tc (32 K). A molecular field coming from the Cu (2) is observed on all the Yb3+ probes in non-superconducting samples with x = 6.0 and 6.5 showing that at these oxygen levels, all the Cu (2)'s are locally magnetically correlated. For x = 6.88 molecular fields suggesting there is phase separation between local magnetic and non-magnetic superconducting regions. For x = 7.0, none of the Cu(2)'s are magnetically correlated. The general features of the oxygen-level dependence of the local magnetic properties are similar in the zinc-substituted and in the zinc-free samples, but magnetic ordering persists to higher oxygen levels when Zn2+ is present.

The R2In compounds (R = rare earth) form an isostructural series which presents a great variety of magnetic behaviors depending on the nature of the rare earth. In this paper we present a study of Er2In by means of magnetic and transport measurements, Mossbauer spectroscopy and neutron diffraction. Our results reveal that this compound orders ferromagnetically below Tc = 40 K: the saturated moments at both the Er3+ sites are 8.0μB and they lie close to the basal plane.

The Kondo lattices YbP and YbN (nonstoichiometric samples) have been investigated by 170Yb Mossbauer spectroscopy, in the temperature range 0.085 K to 80 K in zero magnetic field in YbN and with an applied magnetic field at T=0.045 K in YbP and YbN, and by neutron diffraction in YbN. In both compounds, the antiferromagnetic transition at TN≌0.7 K is first order and occurs through a progressive growth of paramagnetic domains as the temperature increases. The measured exchange interaction is much larger than kBTN in both compounds and it is found to be isotropic in YbP and anisotropic in YbN. The saturated magnetic moment in both compounds is reduced by 50% with respect to the value calculated from the crystal field and exchange interactions. These properties are interpreted in terms of the competition between the Kondo effect and the RKKY exchange interaction; using a model mean field NCA calculation to describe the magnetic phase, the Kondo temperatures TK are found to be near 5–10 K.

We report 170 Yb Mossbauer spectroscopy and magnetisation measurements in the magnetically ordered Kondo lattices YbP, YbN, YbAuCu 4 and YbNiSn, which reveal hybridisation-induced reductions of the Yb spontaneous moment and of the magnetic ordering temperature. Using the self-consistent NCA method with a RKKY derived molecular field, we calculate these reductions and compare them with experiment.

The magnetic properties of the Ni spin chain compounds R 2 BaNiO 5 (R=Gd, Dy, Yb) were investigated by means of Mossbauer spectroscopy and neutron diffraction . The data provide the size and direction of the R magnetic moments and an estimate of the second order CEF parameters. The T -dependence of sublattice magnetizations are discussed in the context of the “Haldane chain in a staggered field” model (Yokoo et al., Phys. Rev. B 58 (1998) 14424).

It has been reported that transport properties of polycrystalline EuPdSb shows anomalies at around 12 and 18 K. Magnetic and transport properties on single crystal of EuPdSb are reported for the first time in this paper. It is revealed that magnetic susceptibility along the a -axis shows strong anisotropy below 12 K. Such features are also observed in high-field magnetization using pulsed field. Especially, three jump steps of magnetization are observed for applying field along the a -axis. 151 Eu Mossbauer study implies that Neel temperature of EuPdSb is 18 K and magnetic phase transition occurs at 12 K, which is consistent with the specific heat measurement.

We present an investigation of the low temperature properties of the ternary intermetallic alloy YbNiSn by X-ray and neutron diffraction, resistivity, magnetisation and 170Yb Mossbauer spectroscopy measurements. It is shown that YbNiSn is a ferromagnet (Tc = 5.65 K) with the Yb3+ magnetic moments lying along the orthorhombic c axis. At low temperatures a strong anisotropy of the interionic exchange coupling is evidenced (λc ≃ 100 kOe/μB, λa ≃ 15 kOe/μB) which competes with the Crystal Electric Field anisotropy (gc ≃ 1.67, ga ≃ 3.72), leading to the unusual situation where the ferromagnetic moments do not lie along the easy magnetisation axis a. Hybridisation of the 4f electrons with band electrons leads to a reduction of the spontaneous moment (saturated value 0.85μB) and is likely to be the origin of the large value of the molecular field constant λc, as well as of the anisotropy of the exchange interaction and of the resistivity.

We have performed Mossbauer measurements on oriented powders of 57Fe-doped La2−xSrxCuO4 (x=0 and 0.2 ) and 57Co-doped La2CuO4. We find that the main axis OZ of the 57Fe electric field gradient in the series lies at an angle β=26°±5° with respect to the crystal c axis, which is much less than recently published values. Our data were corrected for a fraction of unoriented crystallites, which we find to be systematically present, but which was unsuspected in previous experiments. We describe a convenient X-ray examination procedure for detecting and evaluating the unoriented fraction. We discuss possible origins of the angle β and we examine the relative disposition of the direction of c, OZ and of the hyperfine field on 57Fe in La2CuO 4 below TN. We also consider the influence of the oxygen stoichiometry on the symmetry at the Fe site.

From Mossbauer measurements on 166 Er 3+ diluted into YBa 2 Cu 3 O x with x ≅7.0 (superconducting) we obtain the hyperfine tensor and the g tensor of the Er 3+ crystal field ground doublet: A ab = 1610, A c = 935 MHz , g ab = 8.0, g c = 4.5. When the Er 3+ is diluted into a sample with x ≅6.0 (non-superconducting) we find that it now experiences a molecular field of approximately 200 G attributed to a net exchange coupling with its magnetically ordered Cu(2) neighbours. The nonzero value for this field shows that the arrangement of the Cu(2) moments does not have inversion symmetry about the Er 3+ ion. From 166 Er 3+ measurements at 0.05 K on grain oriented ErBa 2 Cu 3 O x ( x ≅7.0 and 6.0) we confirm that for x ≅7.0 the ordered Er 3+ magnetic moments are aligned close to directions perpendicular to the c -axis and we show that for x ≅6.0 the additional Cu(2)-derived molecular field does not modify this alignment. We suggest however, that the appearance of this molecular field as the oxygen level is lowered below x ≅6.4 could be a factor contributing to the known x dependence of the breakdown of the 3-dimensional correlations within the Er 3+ sublattice. For the grain oriented samples we describe an X-ray diffraction analysis procedure which gives a comprehensive assessment of the quality of the grain orientation.

We extend the method used to measure the internal (molecular) field on 170 Yb 3+ diluted for Y 3+ in YBa 2 Cu 3 O x described in the preceding paper (Part 1) to the study of dynamical effects. (The method exploits the field dependence of the 170 Yb 3+ electronuclear levels and the measurements are made by Mossbauer spectroscopy. By studying the fluctuation rates of the Cu(2) derived molecular field acting on the 170 Yb 3+ probes, we follow the fluctuation rates of the short range correlated Cu(2) moments as a function of oxygen content (6.0⩽ x ⩽7.0) and temperature (⪅70 K). When x ∼6.0 the correlated Cu(2) moments are static or fluctuate at frequencies below the lower limit of the accessible window. For x ≅6.35, the average fluctuation rate shows a strong thermal dependence decreasing through the accessible range of 10 12 to 5×10 8 s -1 as the temperature is lowered to 1.4 K and the system shows spin glass-like behaviour. At 1.4 K as x is increased above about 6.5, we observe that a fraction of the probes no long show spin glass-like behaviour and show no evidence of any fields fluctuating in the accessible frequency range. We identify these probes as being situated in the superconducting regions of the sample where at temperatures much lower than the gap there are not expected to be any Cu(2)-based magnetic excitations. From these local probe measurements we find that the amount of the sample that is superconducting depends strongly on x increasing from essentially zero at x ≅6.50 to about 50% at x ≅6.56, to about 75% at x ≅6.66, and reaches 100% as x approaches 7.0. The remaining fraction of the probes which shows a concomitant decrease in importance, continues to show spin glass-like behaviour with a strong thermal dependence of the average local fluctuation rates.

We describe a method, based on the field dependence of the electro-nuclear levels of 170Yb3+ diluted for yttrium in YBa2Cu3Ox, which probes magnetic fields at the rate earth site. Measurements were made using 170Yb Mossbauer spectroscopy. When x ≅ 6.0, we have evidenced an internal (molecular) field on the Yb3+ attributed to the net exchange interaction with the ordered Cu(2) sublattice. The field has an average size of 1600 G and lies at an average angle of near 45° to the c-axis. Up to a least 60 K it remains static on the frequency scale of the experiment (5×108s−1). Some possible origins of this previously unsuspected field are discussed.

The magnetically ordered phase and the Yb 3+ paramagnetic relaxation in the compound YbNi 2 Si 2 have been investigated by 170 Yb Mossbauer spectroscopy between 0.05 and 80 K. The magnetic ordering transition is found to occur at T N = 2.1 K, the Yb 3+ magnetic moments being perpendicular to the fourfold symmetry axis ( c -axis). Above T N and upto 30 K, the thermal variation of the Yb 3+ paramagnetic relaxation rate is a superposition of an interionic exchange term (spin-spin relaxation) and of a T -linear conduction electron-4f spin exchange term (Korringa relaxation).

Experimental data in the hybridized compound YbPd2Si2 is compared with the results obtained with a recently proposed hybridisation model, based on the “large-degeneracy expansion” approximation, which takes into account the crystal field splittings of the rare earth ion energy levels. With a unique set of parameters, satisfactory agreement is simultaneously obtained for the thermal variation of the electronic specific heat, of the magnetic susceptibility and of the electric field gradient at the Yb site, as well as for the field variation of the low temperature magnetisation.

The magnetic properties of Yb 2 BaCuO 5 have been examined using 170 Yb Mossbauer spectroscopy down to 0.05 K and magnetic susceptibility measurements down to 1.5 K. The magnetic polarisation of the Yb 3+ at each of the two sites is due uniquely to couplings with the Cu 2+ moments which are shown to magnetically order at 15 K. The saturated molecular fields at the two Yb 3+ sites are 12 and 22 kG and produce saturated Yb 3+ magnetic moments of 2.2 and 1.1 micro B , respectively.

Using Mossbauer spectroscopy, we follow the thermal dependence of the fluctuation rate of the Cu(2) produced internal (molecular) field acting on a 170 Yb 3+ probe dilutely substituted at the Y 3+ sites. We use the fluctuations of this field to track the collective fluctuations of the nearest neighbour correlated Cu(2) moments. Results are presented for oxygen levels x ⋍ 6.0 and 6.35 and for T ⩽ K.

170 Yb Mossbauer measurements in YbBa 2 Cu 3 O 6 and on Yb 3+ ions substituted into TmBa 2 Cu 3 O 6 show that the ordered Cu(2) sublattice produces a molecular field at the rare earth site. The Yb 3+ ion is not at a centre of magnetic inversion symmetry relative to the Cu(2) moments.

Mossbauer emission measurements show that the isolated 57 Fe 3+ probe pins a Cu spin-glass cluster in superconducting La 2− x Sr x CuO 4 for x x t ( x t is roughly at the centre of the superconducting x range in the phase diagram), whereas for x > x t the probe is essentially coupled with an induced localized Cu magnetic moment.

When the Zn 2+ level is increased in YBa 2 (Cu 1− x Zn x ) 3 O 7 , we observe that the thermal variation of 1/T 1 for the S ′= 1 2 ground state of Yb 3+ probes progressively crosses over from a dependence showing gap-like features ( x = 0) to one showing gapless features ( x = 0.06 and above).

Using Mossbauer spectroscopy, we have followed the internal (molecular) field produced by the short-range correlated Cu(2) moments on 170 Yb 3+ probes diluted at the Y 3+ sites in YBa 2 Cu 3 O x as a function of oxygen level and temperature. At intermediate oxygen levels two local situations coexist, attributed respectively to local magnetic (spin-glass like) and local superconducting behaviour. We monitor the oxygen dependence of the relative amounts of the two fractions.

The compound YbNiSn is studied by means of 170 Yb Mossbauer spectroscopy and single crystal magnetisation measurements. The ferromagnetic Yb 3+ magnetic moment is found to lie along the c -axis and its saturated value is 0.85 μ B . The Curie temperature is T c = 5.65 K. The results show that the exchange coupling is anisotropic and that the ferromagnetic moment is reduced by Kondo fluctuations with a Kondo temperature T 0 = 2 K.

We have measured the low-field (3–30 Oe) magnetisation of GdBa 2 Cu 3 O 7- δ single crystals from 1 K to above T c . T he Gd 3+ contribution cannot be detected when the single crystals are superconducting, while it is easily observed in a superconducting powder. In a single crystal made non-superconducting by deoxygenation, the susceptibility variation is characteristic of Gd 3+ antiferromagnetic ordering along the c -axis. The reduction of the Gd 3+ magnetic response in the superconducting state is found to be related to the amplitude of the shielding effect, even in field-cooled measurements where large flux trapping occurs.

169 Tm Mossbauer measurements are reported for the distorted perovskite compounds TmAlO 3 , TmFeO 3 , TmCrO 3 and TmVO 3 and have been analyzed to provide information concerning the crystal field and magnetic properties of the Tm 3+ ion. Tm 3+ has no magnetic moment in TmAlO 3 and low temperature saturated moments of 0.09, 0.8 and 2.1μ B in TmFeO 3 , TmCrO 3 and TmVO 3 , respectively. In TmFeO 3 and TmCrO 3 the magnitudes and directions of the Tm 3+ moments are examined in terms of previously proposed magnetic structural models. In TmVO 3 , the crystal field properties are very different to those in the ferrite and chromite and a reorientation of the Tm 3+ magnetic moments, accompanied by a sharp increase in their size, is observed near 10 to 15 K.

151 Eu Mossbauer spectroscopy measurements on two amorphous samples of EuPd x ( x = 2.4 and 3.0) prepared by sputtering, show the presence of inhomogeneous mixed valent (Eu 2+ and Eu 3+ ) states with sample averaged valencies 2.25 and 2.85 respectively. Magnetic ordering and hyperfine fields are visible on the Eu 2+ components. The two charge states have the same effective Debye temperature. The amorphous and recrystallised samples are compared.

EPR measurements have been made of the spin Hamiltonian parameters of Mn2+ at the three different sites in each of the four diamagnetic garnets LuAlG, YAlG, LuGaG and YGaG. The temperature variation of all the second order crystal field parameters together with those of the fourth order crystal field parameter and the hyperfine splitting parameter for octahedral sites in YGaG have been followed over a range 4·2-550°K. The magnitude of the various parameters and their temperature variations are discussed.

The dependence of the EPR resonance field on sample shape has been measured for Fe 3+ and Yb 3+ ions substituted into thullium gallium garnet. The results enable the second order paramagnetism of the lowest singlet Tm 3+ energy level to be found.

Measurements of the electric field gradient on 170Yb in YbPd2Si2, YbCu2Si2 and YbCuAl are interpreted within the interconfiguration fluctuation model and provide clear evidence of the persistence of crystal field effects in the Intermediate Valence(IV) state. IV is observed on Yb diluted into TmPd2Si2. The average magnetic hyperfine constant for Yb in YbCuAl has been measured.

170 Yb Mossbauer experiments confirm that the heavy-electron type compound YbP is magnetically ordered below 0.41 K. The saturated spontaneous moment of Yb is much smaller than that of the Yb 3+ Γ 6 doublet, which is the high-temperature ground-state level.

The high critical temperature superconductor YbBa 2 Cu 3 O 7−x has been studied over the range 0.05 to 95K using 170 Yb Mossbauer absorption spectroscopy. Magnetic ordering occurs within the Yb 3+ sublattice at 0.35K. The saturated magnetic moments are 1.7μ B . At all temperatures the hyperfine parameters show the presence of distributions attributed to some disordering of the oxygen vacancies.

170Yb Mossbauer measurements on the heavy-electron compounds YbP, YbAs, and YbSb have probed the competition between RKKY exchange interactions and Kondo hybridisation. Magnetic ordering occurs below TN ∼ 0.5 K with reduced magnetic moments; the RKKY exchange interaction was measured and found to be much greater than kBTN.

169 Tm 3+ Mossbauer quadrupole splitting data for Tm 3 Al 5 O 12 and Tm 3 Ga 5 O 12 measured from 4.2 to 950 K have been analysed to provide crystal field constants for the two lattices which are also compatible with susceptibility data.

In YbPd, 170 Yb Mossbauer measurements show that two different Yb charge states, one magnetic and one non-magnetic, are present in essentially equal proportions. The magnetic fraction, which orders at 1.9 K, shows evidence of 4f-conduction band hybridisation. Both above and below 1.9 K the remaining Yb possess a negligibly small magnetic susceptibility.

Exchange shifts in Tm 3 Ga 5 O 12 have been examined for Cr 3+ and reexamined for Yb 3+ . Line broadening arising from cross relaxation to thermally populated Tm 3+ levels is present for Cr 3+ but absent for Yb 3+ and also for Gd 3+ . These differences cannot be related uniquely to the form of the spectral functions associated with the excited Tm 3+ energy levels.