The Formation of Lithiated Ti-Doped α-Fe2O3 Nanocrystalline Particles by Mechanical Milling of Ti-Doped Lithium Spinel Ferrite

Perturbed Angular Correlation method has been used to study the hyperfine magnetic field in the Heusler alloy Pd₂MnSb(Sn). Ion implantation of the recoil ¹¹¹In nuclei following heavy ion nuclear reactions ¹⁰⁸Pd(⁷Li, 4n)¹¹¹In and ¹⁰⁸Pd(⁶Li, 3n)¹¹¹In has been used to great advantage in the present case resulting in large implantation efficiency. Only a few hours of irradiation time with moderate beam current of the order of 400–500 nA resulted in sufficient implanted ¹¹¹In activity on the sample for good quality measurements. The hyperfine field was measured at ¹¹¹Cd probe nuclei substituting Mn and Sb(Sn) sites as a function of temperature. The fraction of ¹¹¹Cd nuclei occupying Mn atom sites was found to increases with the annealing of sample at higher temperatures.     

Electric field gradients of 111Cd in the copper oxides CuO and Cu2O

Perturbed angular correlation measurements were performed after ¹¹¹In implantation into CuO and Cu₂O powder samples and 1 μm thick Cu₂O surface layers. The quadrupole hyperfine interaction of ¹¹¹Cd was studied in isochronal annealing cycles at 370–1170 K covering the CuO→Cu₂O phase transition. The electric field gradients obtained for ¹¹¹Cd on substitutional Cu lattice sites were associated with the repective oxygen coordinations. Annealing of Cu₂O surface layers on copper foils resulted in a texture with the efg pointing preferentially out of the surface plane.     

Damage studies on the system^{111} \mathop {In}\limits^ \to \underline {Ni}

Lattice damage after implantation of¹¹¹In in Ni has been studied applying the DPAC technique to the 171–245 keV -ray cascade in the daughter nucleus¹¹¹Cd. Implantations were carried out at 10 K and at 300 K. The low temperature implantation yields a higher regular substitutional fraction (80%) than the room temperature implantation (40%). The annealing behaviour of both implants above RT is the same. In addition, two distinct defect-associated sites were observed in isochronal annealing sequences. A microscopic model for these defects is presented, which takes into account magnetic and electric hyperfine interaction strengths, binding energies and site populations as a functions of temperature.     

The magnetic hyperfine field at Cd nuclei in the rare earth ferromagnets Gd,Tb, Dy,Ho, Er and Tm

The time differential perturbed angular correlation technique has been used to study the combined magnetic and electric hyperfine interactions at the site of a¹¹¹Cd impurity in the rare earth ferromagnets Gd, Tb, Dy, Ho, Er, and Tm at 4.2 °K. The following magnetic hyperfine fields at the site of¹¹¹Cd have been found: ¦H _hf ¦=340(7) kG in Gd, 275 (5) kG in Tb, 221 (4) kG in Dy, 116 (3) kG in Er and 60 (6) kG in Tm. In Ho two magnetically different sites were observed with magnetic fields of 159 (3) and 139 (3) kG. Both sites are equally populated. The coupling constantJ _5f of the conduction electron-4f interaction has been calculated for the different rare earth metals from the measured hyperfine fields by means of the RKKY theory.     

Hyperfine Fields at the Cd Site in La0.67Cd0.25MnO3 CMR Manganites

Although Cd and Ca ions have the same valence and cation size, their incorporation into vacancy-doped La manganites induce different properties. While the incorporation of Ca leads to high Tc up to 250 K and induces a metallic-like behaviour, the incorporation of Cd severely reduces Tc and promotes insulator-like behaviour. In this work, the Cd hyperfine fields have been measured with the Perturbed Angular Correlations (PAC) technique after implantation and annealing of ^111m Cd in La–Cd–MnO₃ samples. The PAC results are compared with measurements of the resistivity and magnetization performed on the same samples. The mixed La and Mn site Cd occupancy is suggested as a possibility to explain the properties of the La–Cd–MnO₃ system.     

Ferromagnetic Semiconductors Studied by Hyperfine Interaction of Nuclear Probes

The ferromagnetic spinels CdCr₂Se₄ and CuCr₂Se₄ were investigated by PAC (perturbed angular correlations) after implantation of the probes ¹¹¹In(¹¹¹Cd), ^111mCd, ¹¹¹Ag(¹¹¹Cd) and ⁷⁷Br(⁷⁷Se). The site occupation of different probes was determined by magnetic and electric hyperfine interactions. Theoretical calculations of hyperfine parameters by the WIEN97 code gave satisfactory efg (electric field gradients) but the magnetic hyperfine fields are inconsistent with the experiments. This revised version was published online in September 2006 with corrections to the Cover Date.     

Magnetic hyperfine fields at Gd and in sites in GdPdIn compound

Perturbed gamma-gamma angular correlation (PAC) technique was used to measure the hyperfine interactions in the intermetallic compound GdPdIn using ¹¹¹In→ ¹¹¹Cd and ¹⁴⁰La→ ¹⁴⁰Ce probe nuclei at the In and Gd sites, respectively. The PAC results for ¹¹¹Cd show two well-defined electric quadrupole frequencies above T _C assigned to probes occupying Gd and In sites, with ~50% of site occupation each. The fraction corresponding to In sites increases with temperature reaching 95% around 500 K. Below T _C the measurements for ¹¹¹Cd probe showed combined electric quadrupole plus magnetic dipole interaction with sharp increase in the magnetic field below around 80 K. A pure magnetic interaction with lower hyperfine field values was observed at the Gd sites occupied by ¹⁴⁰Ce below 100 K.     

Magnetic and electric hyperfine interactions of181Ta implanted in thulium

The magnetic and electric hyperfine interaction at the site of dilute¹⁸¹Ta impurities in the rare earth metal Tm has been investigated as a function of temperature by TDPAC measurements. The samples were prepared by ion implantation of radioactive¹⁸¹Hf. In the paramagnetic phase between 100 K and 700 K the electric fieldgradient is a linear function of temperature: V_zz(T)=V_zz(O)·(1-A·T) with A=4.6·10^?4K^?1 and V_zz(293K)=6.4 (4)·10¹⁷v/cm². The TDPAC spectrum observed at 4.2 K reflects the 4 magnetically non-equivalent sites for an impurity in magnetically ordered Tm. The relative values and amplitudes of the corresponding 4 magnetic hyperfine fields are consistent with the predictions of the RKKY theory.     

Perturbed angular correlation experiments on111In in oxidized AgCd alloy

The hyperfine interaction of¹¹¹Cd probes in preoxidized and α-irradiated Ag_0.94Cd_0.06 alloy has been investigated by PAC measurements and compared with the results for pure Ag. Several probe atom sites were distinguished and characterized by their hyperfine parameters and temperature evolution. The different behavior of In-oxygen and In-oxygen-vacancy complexes in AgCd and Ag was found and discussed. A considerable influence of the irradiation temperature and sample thickness on the different In-oxygen-vacancy complexes formation was evidenced. The parameters of¹¹¹Cd quadrupole interaction measured during isochronal annealing studies in preoxidized and deuteron irradiated AgCd were very similar to the ones observed after α-irradiation.     

Hyperfine-field measurements inCr Rh andCr Re alloys using perturbed angular correlation technique

The hyperfine fields on¹¹¹Cd probe nuclei in Cr (1 at% Rh), Cr (0.3 at% Rh) and Cr (0.5 at% Re) matrices are measured using time-differential perturbed (–) angular correlation of 173–247 keV cascade in the decay of¹¹¹In to the levels in¹¹¹Cd. The sources prepared by ion implantation of¹¹¹In (2.81 d) activity followed by appropriate annealing procedure were found to be of good quality. The addition of impurities, located to the right of chromium in the periodic table such as Rh and Re, to the chromium matrix increases the electron to atom ratio, resulting in an increase in the magnetic moment compared to pure chromium. This in turn is expected to result in an increase in the hyperfine fields at probe nuclei in these alloys. The measured hyperfine fields are in qualitative agreement with the expected changes in these alloys.On leave from Kanpur Institute of Technology.     

Spin and temperature dependence of the magnetic hyperfine field of Cd in the rare earth-aluminum Lavesphase compounds RAl2

Perturbed angular correlation spectroscopy has been used to investigate the combined magnetic and electric hyperfine interaction of the probe nucleus ¹¹¹Cd in ferromagnetically ordered rare earth (R)-dialuminides RAl₂ as a function of temperature for the rare earth constituents R=Pr, Nd, Sm, Eu, Tb, Dy, Ho and Er. In compounds with two magnetically non-equivalent Al sites (R=Sm, Tb, Ho, Er), the magnetic hyperfine field was found to be strongly anisotropic. This anisotropy is much greater than the anisotropic dipolar fields, suggesting a contribution of the anisotropic 4f-electron density to magnetic hyperfine field at the closed-shell probe nucleus. The spin dependence of the magnetic hyperfine field reflects a decrease of the effective exchange parameter of the indirect coupling with increasing R atomic number. For the compounds with the R constituents R=Pr, Nd, Tb, Dy and Ho the parameters B₄, B₆ of the interaction of the crystal field interaction have been determined from the temperature dependence of the magnetic hyperfine field. The ¹¹¹Cd PAC spectrum of EuAl₂ at 9 K confirms the antiferromagnetic structure of this compound.     

Conversion electron Mössbauer spectroscopic study of YIG substituted with Bi,Ti, Ga and La

YIG films, substituted with Bi, Ti, Ga and La, were grown on a (111) plane of Gd₃Ga₅O₁₂ or (Gd, Ca)₃(Ga, Mg, Zr)₅O₁₂ by a liquid phase epitaxial method. With the increase of the concentration of Bi atoms, which are substituted at 24c sites of YIG, the magnetic hyperfine fields at 16a and 24d Fe sites increased and the direction of magnetic moments changed from parallel to 45° to the (111) plane. With the increase of Ga concentration, the hyperfine fields at 16a and 24d Fe sites decreased. The hyperfine interaction and the substitution effect of YIG films are discussed.     

High Pressure Mössbauer Studies on FCC Fe53Ni47 Alloy

Perturbed angular correlation measurements of the hyperfine interaction of ¹¹¹In in sapphire show, that after implantation and annealing at 1000°C, the fraction of undisturbed probe atoms exhibiting a unique quadrupole interaction with ν _Q = 219(1) MHz (η = 0) varies between 50% at 4 K, 5% at 100 K and 80% at 973 K in a reversible manner. A possible explanation for this surprising behaviour is the influence of so-called ‘after effects’ following the EC-decay of ¹¹¹In to ¹¹¹Cd. Immediately after the decay the ¹¹¹Cd is in an ionized state, then collects electrons from its surroundings and reaches the ground state. The different electronic configurations that arise during this relaxation process affect the amplitude (f _u) and the damping (δ _u) of the unique quadrupole interaction.     

Hyperfine Interactions in CeT2Ge2 (T = Mn,Co) Heavy Fermions Compounds Measured by TDPAC

Time Differential Perturbed γ–γ Angular Correlation (TDPAC) technique was used to measure the magnetic hyperfine field at both Ge and Ce sites in CeMn₂Ge₂ and CeCo₂Ge₂ intermetallic compounds. The ¹¹¹In (¹¹¹Cd) probe nuclei was used to investigate the hyperfine interaction at Ge sites, while the ¹⁴⁰La (¹⁴⁰Ce) nuclei was used to measure the magnetic hyperfine field at Ce site. The present measurements cover the temperature ranges from 10–460 K for CeMn₂Ge₂ and 9–295 K for CeCo₂Ge₂, respectively. The result for ¹¹¹Cd probe showed two distinct electric quadrupole frequencies above magnetic transition temperatures, in both compounds and a combined interaction in the magnetic region. The temperature dependence of the magnetic hyperfine field at ¹¹¹Cd at Mn site for the CeMn₂Ge₂ compound showed a transition from ferromagnetic to antiferromagnetic phase around 320 K and from antiferromagnetic to paramagnetic phase at 420 K. While a small magnetic field was measured on ¹¹¹Cd at Co site, no magnetic field on ¹⁴⁰Ce site was observed in CeCo₂Ge₂. This revised version was published online in September 2006 with corrections to the Cover Date.     

Mössbauer effect study of Gadolinium Iron Garnet

The Mossbauer Effect study of polycrystalline Gadolinium Iron Garnet has been undertaken between 714K and 4.2K. The temperature dependence of the sublattice magnetization has been determined at the two iron sites and the direction of the hyperfine fields at each site is [111] over the entire temperature range. The saturation fields at the octahedral and tetrahedral sites are respectively 547 kOe and 477 kOe. The ferrimagnetic Neel temperature has been found to be 562.5K and above this temperature, the quadrupole splitting at the octahedral and tetrahedral sites are –0.43 mms^–1 and ¦0.89¦mms^–1 respectively.     

Hf3Al2 and Zr3Al2 Isostructural Aluminides Studied by PAC with 181Ta and 111Cd Probes

The electric quadrupole hyperfine interactions for ¹⁸¹Hf/¹⁸¹Ta and for ¹¹¹In/¹¹¹Cd probes in polycrystalline Zr₃Al₂ and Hf₃Al₂ compounds were measured in the temperature range 24–1100 K. The hyperfine quadrupole interaction parameters were determined after different doping techniques and heat treatments of the samples.¹⁸¹Hf/¹⁸¹Ta was found to substitute the Hf/Zr sites and the ¹¹¹In/¹¹¹Cd impurities appear to substitute both the 8(j) Al sites and the three nonequivalent Hf/Zr sites.     

Investigation of the impurity hyperfine field polarization in polycrystalline Rare Earth ferromagnets

Time differential perturbed angular correlation spectra of¹¹¹Cd in ferromagnetic polycrystalline Dy have been measured at 4.2 K in external magnetic fields up to 60 kG. The experimental data were well reproduced by a calculation which assumed that the angular distribution of the magnetic hyperfine fields is identical to that of the magnetic moments of the 4f-shells. The distribution of the 4f-moments was derived from magnetic anisotropy data. The results of this work seem to justify the application of the integral perturbed angular correlation technique for the determination of magnetic hyperfine fields in incompletely polarized ferromagnetic samples. The magnetic hyperfine fields of¹⁷⁷Hf:Gd and¹⁷⁷Hf:Dy have been measured by this method as:H _hf(Hf:Gd)=–375(60)kG andH _hf(Hf:Dy)=–225(45)kG.     

111Cd hyperfine probes in YBaCuO

Different techniques like implantation or in-diffusion have been applied to place the hyperfine probe¹¹¹Cd at YBaCuO lattice sites. In this paper different experiments are reviewed which show that the standard PAC-probe can be placed at any regular site of YBaCuO. The PAC-parameters of these sites are collected and discussed. This work was supported by the BMFT, contract: FKZ 13 N 54930     

Phase transitions in the SrHfO3 perovskite measured with 111In/111Cd PAC

The temperature dependence of the hyperfine parameters in SrHfO₃ powder samples has been investigated by means of Perturbed Angular Correlation spectroscopy using implanted ¹¹¹In probes. Three quadrupole interactions have been established, with the largest fraction showing a pronounced dynamic interaction. We assign this fraction to ¹¹¹In / ¹¹¹Cd probe atoms on substitutional Hf sites. The temperature dependence of the dynamic interaction has been associated to the Pnma↔Imma phase transition at ∼700 K. We discuss the results in relation to those obtained for ¹⁸¹Hf / ¹¹¹Ta-probes in AHfO₃ (A=Ba, Sr, Ca) and for ¹¹¹In / ¹¹¹Cd-probes in PbZrO₃ and BaTiO₃. This revised version was published online in August 2006 with corrections to the Cover Date.     

Study of hyperfine interactions in the intermetallic compound CePd2Si2 using PAC technique with 111Cd as probe nuclei

Perturbed γ???γ angular correlation spectroscopy (PAC) has been used to investigate the hyperfine interactions in the intermetallic compound CePd₂Si₂ using ¹¹¹In→¹¹¹Cd probe nuclei. Samples of CePd₂Si₂ were prepared by melting constituent elements in an arc furnace under pure argon atmosphere. Carrier-free ¹¹¹In nuclei were introduced into the samples by thermal diffusion at 800°C in vacuum during 12 h. The measurements were performed in the temperature range of 4.2–300 K. Above the magnetic transition temperature (T _N ?=?10 K), the results show two distinct and well defined quadrupole interactions that were assigned to probe nuclei occupying Ce and Si sites in the compound. The quadrupole frequencies were found to decrease linearly with increasing temperature. The PAC spectra taken below 10 K were analyzed with a model including combined electric quadrupole plus magnetic dipole interactions, from which the hyperfine magnetic field was determined.