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Due to its rich variety of electromagnetic properties, such as a colossal magnetoresistance, charge and orbital ordering, and metal-insulator transition, the magnetic behavior in La0.5Ba0.5MnO3 double perovskite compounds has been investigated by several techniques, however more experimental data, especially from atomic resolution techniques, are still necessary to understand such complex behavior. In this paper, we have used a nuclear and short-range technique, the Perturbed Angular Correlation (PAC) spectroscopy, to investigate the magnetic hyperfine interaction at the 140Ce and 111Cd probe nuclei as impurities occupying La sites. This double perovskite samples were synthesized by Sol-Gel route. The crystal structure was determined by X-ray diffraction and the analyses showed that this method produced perovskite oxides with cubic structure in Pm-3m space group and the homogeneity was determined by Transmission Electron Microscopy (TEM). The local properties investigated by PAC spectroscopy revealed a ferromagnetic transition temperature above 300 K and a pure antiferromagnetic interaction below 100 K. Moreover, it also indicates an anomalous behavior of the temperature dependence of magnetic hyperfine field at La sites measured with 140Ce probe nuclei, which can be ascribed to the contribution of 4f band of Ce to Magnetic Hyperfine Field (Bhf) at low temperatures due to the increase in its localized character.Due to its rich variety of electromagnetic properties, such as a colossal magnetoresistance, charge and orbital ordering, and metal-insulator transition, the magnetic behavior in La0.5Ba0.5MnO3 double perovskite compounds has been investigated by several techniques, however more experimental data, especially from atomic resolution techniques, are still necessary to understand such complex behavior. In this paper, we have used a nuclear and short-range technique, the Perturbed Angular Correlation (PAC) spectroscopy, to investigate the magnetic hyperfine interaction at the 140Ce and 111Cd probe nuclei as impurities occupying La sites. This double perovskite samples were synthesized by Sol-Gel route. The crystal structure was determined by X-ray diffraction and the analyses showed that this method produced perovskite oxides with cubic structure in Pm-3m space group and the homogeneity was determined by Transmission Electron Microscopy (TEM). The local properties investigated by PAC spectroscopy revealed a fe...

In the work here reported, we have calculated magnetic hyperfine interactions in rare-earth (R) intermetallic compounds by using the free open-source all-electron ELK code. The RCd (R = Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb) series was chosen as a test system because an almost complete set of experimental data on the hyperfine parameters at Cd sites was acquired through the time differential perturbed angular correlation (TDPAC) spectroscopy as previously reported. Moreover, results on magnetic hyperfine field (Bhf) from WIEN2k code were also reported allowing a qualitative comparison analysis. We emphasize that the utilized version of ELK accounted for the contact field only. Yet, as it is the only contribution expected for Cd site in RCd compounds, the calculated Bhf values are in reasonable agreement with the experimental results. The Spin-orbit coupling when taken into account led to a decrease in deviation from experimental data. Addition, the Hubbard-like term was revealed crucial in order to make Bhf predictions for CeCd, suggesting that this behavior may be associated with a weaker 4f electron localization in Ce.

GdMnIn is reported to crystallize in the hexagonal MgNi2-type structure presenting a spin-glass behavior with no magnetic order attributed to the triangular spin frustration of magnetic ions. In the present work, FC-ZFC magnetization, specific heat and AC susceptibility measurements along with the local magnetic exchange measured by hyperfine interactions at In sites are used to investigate the magnetic behavior in GdMnIn compound. The ZFC-FC magnetization curves exhibit an inflection which was ascribed to the antiferromagnetic transition at TN= 145 K. These curves also give an indication of thermomagnetic irreversibility at 118 K, which along with the absence of inflection in specific heat results might be associated to spin-glass behavior. Results of AC susceptibility and magnetic hyperfine field measured using 111In(111Cd) probe nuclei carried out by perturbed angular correlations (PAC) technique did not show evidence of spin-glass behavior. The thermomagnetic irreversibility in FC-ZFC curves along with results of hyerfine interactions suggest the presence of magneto-crystalline anisotropy effects and a weak long-range coupling in GdMnIn.

Nanoparticles (NPs) that combine biocompatibility and enhanced physical characteristics for biomedical applications are currently an area of intense scientific research. Hafnium oxide NPs are an innovative approach in the anticancer treatment by radiotherapy due to their low toxicity and enhancement of local dose in the tumor reducing the total radiation dose for the patient. The combination of this property with the excellent magnetic hyperthermia performance of Fe3O4 NPs can produce a promising nanomaterial for cancer therapy. In this work, we attempted to synthesize nanoscale samples of HfO2 doped with nominal 10 at.% Fe, and Fe3O4 doped with Hf at 10 at.% level using simple chemical routes. The crystal structure of the samples was characterized by X-ray diffraction. The material was irradiated with neutrons in a research reactor, the nuclear reaction 180Hf(n, γ)181Hf yielding the probe nucleus 181Hf(181Ta) used in the perturbed angular correlations experiments to measure hyperfine interactions. Despite their immediate response to the external magnetic field, at local level both samples showed only electric quadrupole interaction typical of the monoclinic hafnia indicating that Fe replaces Hf in HfO2 NPs, but, rather than substituting Fe, Hf enters magnetite in the form of HfO2 clusters. Transmission Electron Microscopy was exploited to study the morphology of these complex systems, as well as to localize hafnia clusters and understand the nature of their coupling to Fe3O4 specks.

In order to understand the interaction mechanisms in RE2O3 (RE=Gd, Er) nanoparticles (NPs), Perturbed Angular Correlation (PAC) spectroscopy, a local technique, plus external magnetic field, was used to elucidate local interactions and possible mapping of the different contribution in these compounds. NPs were synthesized by thermal decomposition and characterized by transmission electron microscopy and X-ray diffraction. PAC measurements were performed using 111In(111Cd) as probe nuclei, with and without the application of an external magnetic field (EMF) of 0.5 T in different temperatures (50 K, 100 K, 200 K, 300 K). Results show that the hyperfine magnetic field is almost zero when the probe is located at the symmetric site, and ∼4 T and ∼5 T for Gd2O3 and Er2O3, respectively, when the probe occupies the asymmetric field.

LaMnO3+δ is a complex oxide, which, depending on the oxygen excess concentration, presents different crystalline structure and interesting magnetic and electric properties such as colossal magnetoresistance, polaron dynamics, multiferroic behavior, and charge-orbital ordering. This complexity requires different characterization techniques to draw a picture as complete as possible allowing a good understanding of these phenomena. Here, we have used the perturbed angular correlation (PAC) technique to measure hyperfine interactions at La and Mn sites of LaMnO3+δ(δ ∼0.15) using 140Ce and 111Cd at La sites as probe nuclei in order to investigate within an atomic scale the magnetic and electric interactions in this compound. The results show that 111Cd nuclei occupy highly symmetric local sites in agreement with a rhombohedral structure. The magnetic hyperfine field (Bhf) measured with 111Cd at La sites is very small (Bhf = 0.40 T) due to the supertransferred magnetic field from Mn neighbors through oxygen orbitals. On the other hand, 140Ce nuclei at La sites present a saturation field of around 3.7 T much higher than that expected for La sites (due to the weak transfer field by superexchange mechanism). In addition, for temperature range above the magnetic ordering (200-300 K) a dynamic hyperfine interaction was observed characterized by the attenuation parameter λ(T) whose temperature dependence allowed to determine the activation energy (Ea) associated to charge transfer. The polarization of the 4f-electron of Ce impurities affects the local magnetic field at impurity sites as well as the Ea.

In this paper, we investigate the effects of doping in the local structure of SnO2 by measuring the hyperfine interactions at impurity nuclei using the Time Differential Perturbed Gamma-Gamma Angular Correlation (TDPAC) method in addition to density functional theory simulations. The hyperfine field parameters have been probed as a function of the temperature in thin film samples. The experimental results reveal that 117Cd/In and 111In/Cd are incorporated and stabilized in the SnO2 lattice replacing the cationic site. Significant differences in the electric field gradient were observed from TDPAC measurements with both the probe nuclei. Furthermore, the absence of strongly damped spectra further indicates that implanted Cd atoms (for 117Cd/In probe nuclei measurements) easily occupy regular substitutional Sn sites with good stability. The simulated value for the electric field gradient obtained with the first oxygen neighbor removed is closer to the experimental value observed for 117Cd, which also indicates this configuration as stable and present in the sample.

Here we report time differential perturbed angular correlation (TDPAC) results of Co-doped SnO2 thin films. Making use of stable Co and radioactive 111In implanted at the Bonn Radioisotope Separator with energies of 80 keV and 160 keV, respectively, it was possible to study the dopant incorporation and its lattice location during annealing. The hyperfine parameters have been probed as a function of temperature in vacuum. Two quadrupole interactions were observed. At high temperatures the dominant fraction for the probe nuclei can be assigned to the Cd-incorporation at the cation substitutional site in a highly disordered structure, obtained after implantation, to high crystallinity for the measurements at 873 K and 923 K. The similarity in TDPAC spectra obtained in undoped SnO gives indirect evidence that In and Co diffuse to different depths during the annealing process. Other interpretations will be discussed. OA gold

The local environment in titanium dioxide was studied by the time dependent perturbed γ-γ angular correlation of 111In/111Cd and 181Hf/181Ta at the Helmholtz-Institut fur Strahlen-und Kernphysik, Bonn. An introduction to the implantation methodologies performed at the Bonn Radioisotope Separator is presented. The investigation was carried out on thin films, which were deposited by magnetic sputtering on Si. The results show two different sites for both probe nuclei with unique electric quadrupole interaction. Using 111Cd one of them has been attributed to the substitutional Ti at the rutile structure. For 181Ta, the spectra show the anatase phase, with a well-defined electric quadrupole frequency.

Magnetic hyperfine field has been measured in the orthorhombic intermetallic compound LaMnSi2 with perturbed angular correlation (PAC) spectroscopy using radioactive 140La(140Ce) nuclear probes. Magnetization measurements were also carried out in this compound with MPSM-SQUID magnetometer. Samples of LaMnSi2 compound were prepared by arc melting the component metals with high purity under argon atmosphere followed by annealing at 1000°C for 60 h under helium atmosphere and quenching in water. X-ray analysis confirmed the samples to be in a single phase with correct crystal structure expected for LaMnSi2 compound. The radioactive 140La (T1/2 = 40 h) nuclei were produced by direct irradiation of the sample with neutrons in the IEA-R1 nuclear research reactor at IPEN with a flux of ∼ 1013 n cm−2s−1 for about 3 - 4 min. The PAC measurements were carried out with a six BaF2 detector spectrometer at several temperatures between 10 K and 400 K. Temperature dependence of the hyperfine field, Bhf was found to be anomalous. A modified two-state model explained this anomalous behavior where the effective magnetic hyperfine field at 140Ce is believed to have two contributions, one from the unstable localized spins at Ce impurities and another from the magnetic Mn atoms of the host. The competition of these two contributions explains the anomalous behavior observed for the temperature dependence of the magnetic hyperfine field at 140Ce. The ferromagnetic transition temperature (TC) of LaMnSi2 was determined to be 400(1) K confirming the magnetic measurements.Magnetic hyperfine field has been measured in the orthorhombic intermetallic compound LaMnSi2 with perturbed angular correlation (PAC) spectroscopy using radioactive 140La(140Ce) nuclear probes. Magnetization measurements were also carried out in this compound with MPSM-SQUID magnetometer. Samples of LaMnSi2 compound were prepared by arc melting the component metals with high purity under argon atmosphere followed by annealing at 1000°C for 60 h under helium atmosphere and quenching in water. X-ray analysis confirmed the samples to be in a single phase with correct crystal structure expected for LaMnSi2 compound. The radioactive 140La (T1/2 = 40 h) nuclei were produced by direct irradiation of the sample with neutrons in the IEA-R1 nuclear research reactor at IPEN with a flux of ∼ 1013 n cm−2s−1 for about 3 - 4 min. The PAC measurements were carried out with a six BaF2 detector spectrometer at several temperatures between 10 K and 400 K. Temperature dependence of the hyperfine field, Bhf was found to be a...

The TDPAC technique was applied to verify a hypothesis about the influence of electron capture after-effects on the integrity of radiometal complexes with organic ligands in aqueous solutions. The neutral aqueous solutions of DTPA-complexes with two parent isotopes, 111 In(EC) 111 Cd and 111m Cd, were used for direct comparison of dynamic interaction parameters. Data for the parent 111 In–DTPA complexes revealed three fractions with essentially different relaxation constants, including an “unperturbed” fraction, which, according to the hypothesis, is due to small fragments of the initial complexes disintegrated as a result of Auger-process and the following Coulomb fragmentation. Only one fraction with a relaxation constant of 3(1)×10 6 s −1 was observed for the 111m Cd–DTPA solution confirming the proposal about the influence of electron capture after-effects. Measurements with the frozen solutions allowed determining the electric field gradient (EFG) at Cd-sites in complexes with DTPA, V zz =6.7(2)×10 21 V/m 2 with an asymmetry parameter η =0.75(5).

In this paper, the effect in structural and magnetic properties of iron doping with concentration of 20% in hafnium dioxide (HfO2) nanoparticles is investigated. HfO2 is a wide band gap oxide with great potential to be used as high-permittivity gate dielectrics, which can be improved by doping. Nanoparticle samples were prepared by sol-gel chemical method and had their structure, morphology, and magnetic properties, respectively, investigated by X-ray diffraction (XRD), transmission electron microscopy (TEM) and scanning electron microscopy (SEM) with electron back scattering diffraction (EBSD), and magnetization measurements. TEM and SEM results show size distribution of particles in the range from 30 nm to 40 nm with small dispersion. Magnetization measurements show the blocking temperature at around 90 K with a strong paramagnetic contribution. XRD results show a major tetragonal phase (94%).

The magnetic properties of PrMn2Ge2 compound have been investigated by perturbed γ−γ angular correlation (PAC) spectroscopy using 111In(111Cd) as probe nuclei as well as by magnetization measurements. This ternary intermetallic compound exhibits different magnetic structures depending on the temperature. The magnetic ordering is mainly associated with the magnetic moment of 3d-Mn sublattice but at low temperatures a magnetic contribution due to ordering of the magnetic moment from 4f-Pr sublattice appears. PAC results with 111Cd probe nuclei at Mn sites show that the temperature dependence of hyperfine field Bhf(T) follows the expected behavior for the host magnetization, which could be fitted by two Brillouin functions, one for antiferromagnetic phase and the other for ferromagnetic phase, associated with the magnetic ordering of Mn ions. Magnetization measurements showed the magnetic behavior due to Mn ions highlighting the antiferromagnetic to ferromagnetic transition around 326 K and an increase in the magnetization around 36 K, which is ascribed to Pr ions ordering.

The electric field gradient (efg) at the Nb site in the intermetallic compounds Nb3X (X = Al, In, Si, Ge, Sn) was measured by the Perturbed Angular Correlation (PAC) method using the well-known gamma-gamma cascade of 133 -482 keV in 181Ta from the β- decay of 181Hf, substituting approximately 0.1 atom percent of Nb. The PAC results show that Vzz drops by nearly 40% when X changes from Al to In, and by about 25% when X changes from Si to Ge and Sn. This behavior is most probably related to the change in the degree of sp hybridization in these compounds. The Vzz values of the studied compounds do not follow the well known universal correlation for the efg's in non-cubic metals but the observed trend is well reproduced by results of ab-initio electronic structure calculations. In the case of Nb3 Al a linear temperature dependence of the quadrupole frequencies was observed in the temperature range of 6.5 to 1210 K.

The magnetic behavior of Gd2O3 nanoparticles, produced by thermal decomposition method and subsequently annealed at different temperatures, was investigated by magnetization measurements and, at an atomic level, by perturbed γ − γ angular correlation (PAC) spectroscopy measuring hyperfine interactions at 111In(111Cd) probe nuclei. Nanoparticle structure, size and shape were characterized by X-ray diffraction (XRD) and Transmission Electron Microscopy (TEM). Magnetization measurements were carried out to characterize the paramagnetic behavior of the samples. XRD results show that all samples crystallize in the cubic-C form of the bixbyite structure with space group Ia3. TEM images showed that particles annealed at 873 K present particles with highly homogeneous sizes in the range from 5 nm to 10 nm and those annealed at 1273 K show particles with quite different sizes from 5 nm to 100 nm, with a wide size distribution. PAC and magnetization results show that samples annealed at 873 and 1273 K are paramagnetic. Magnetization measurements show no indication of blocking temperatures for all samples down to 2 K and the presence of antiferromagnetic correlations.

The magnetic hyperfine field (Bhf) in ferrimagnetic GdCo5 compound has been investigated as a function of temperature by Mossbauer effect (ME) spectroscopy and perturbed angular correlation (PAC) spectroscopy using 119Sn and 111Cd probe nuclei, respectively. Results show that the non-magnetic probe atoms 119Sn and 111Cd substitute all three non-equivalent positions in GdCo5: Gd, CoI, and CoII. For 119Sn and 111Cd probes at Gd sites, the saturation magnetic hyperfine fields are very different with values of Bhf1 = 57.0(1) T and Bhf1= 20.7(1) T, respectively. For 119Sn and 111Cd atoms localized at CoI and CoII sites the magnetic hyperfine fields are practically identical and, in saturation, reach the values of Bhf2 = 11.6(1) T and Bhf2 = 11.1(2) T, and Bhf3 = 14.8(1) T and Bhf3 = 14.4(2) T, respectively.

The magnetic behavior of the intermetallic compound NdMn2Ge2 was investigated by bulk magnetization measurements and measurements of hyperfine interactions using perturbed γ–γ angular correlation (PAC) spectroscopy. Magnetization measurements indicate the presence of four magnetic transitions associated with the Mn and Nd magnetic sublattices. At high temperatures, magnetic measurements show a change in the slope of the magnetization due to an antiferromagnetic transition around TN ∼ 425 K and a well defined ferromagnetic transition at TC ∼ 320 K. Moreover, at ∼210 K a peak is observed in the magnetization curve, which is assigned to the reorientation of the Mn spin, and at ∼25 K an increase in the magnetic moment is also observed, which is ascribed to the ordering of Nd ions. PAC measurements using 140La(140Ce) and 111In(111Cd) probe nuclei allowed the determination of the temperature dependence of the magnetic hyperfine field (Bhf) at Nd and Mn sites, respectively. PAC results with 111Cd probe nuclei at...

In this paper, the local magnetic properties of La-doped Fe3O4 (5% and 10%) bulk and Nanoparticles (NPs) samples were studied by measuring hyperfine interactions in a wide range of temperature from 10 to 900 K with perturbed γ-γ angular correlation spectroscopy using 111In(111Cd) and 140La(140Ce) as probe nuclei. Results for the temperature dependence of the magnetic hyperfine field (Bhf) for bulk and NP samples, pure and doped with La show that its behavior follows a second order Brillouin-like transition from which the Curie temperature (TC) was determined (TC ∼ 855 K). Results also show two different regions in NP samples: the core where a minor fraction of probe nuclei with well defined magnetic dipole frequency was observed and the shell where a major fraction with broad distributed electric quadrupolar frequency (surface effect in NP) was observed. The Verwey transition TV ∼ 120 K, due the order disorder phase, was also observed in all samples. The results are discussed in terms of the magnetic exch...

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 implant 111In probes in the Heusler alloys Pd2MnZ(Z=Sn,Sb,Ge,In). Perturbed Angular Correlation method was used to study the hyperfine magnetic field in these alloys. Direct implantation of 111In probe nuclei was 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 111In probe nuclei substituting Mn and Z sites as a function of temperature. The fraction of 111In nuclei occupying Mn atom sites was found to increases with the annealing of sample at higher temperatures.

We performed the first-principles band-structure calculations for a pure and a Cd-doped AgInO2 delafossite compound. The results are carefully analyzed and compared with the results obtained for a pure and a Cd-doped CuAlO2 compound, calculated previously by our group. The electronic structures of both systems are found to be similar in many details, being characterized by the same hybridization scheme that occurs at both Cu and Ag positions. Introduction of Cd impurity into the Cu site produces a shallow band within the CuAlO2 gap, while the Cd presence at the Ag site creates a wide band pinned at the Fermi level in the AgInO2 spectrum. In both cases, however, the n-type conductivities are predicted.

A special target chamber for the direct production & recoil implantation of radioactive probes for perturbed angular correlation has been constructed and tested. Feasibility studies were made by reproducing the known quadrupole frequencies at 77Br and 111In probes in metallic zinc. Preliminary results were obtained on the lattice site dependence of Cd hyperfine field in Pd2MnSn Heusler alloy with the PAC technique.

The temperature dependence of the magnetic hyperfine field (Bhf) at Mn atom sites was measured in LaMn2(Si(1−x)Gex)2, with 0 ≤ x ≤ 1, compounds with perturbed γ−γ angular correlation spectroscopy using 111In(111Cd) as probe nuclei in the temperature range from 20 K to 480 K. The results show a transition from antiferromagnetic to ferromagnetic ordering for all studied compounds when Ge gradually replaces Si and allowed an accurate determination of the Neel temperature (TN) for each compound. It was observed that TN decreases when Ge concentration increases. Conversely, the Curie temperature increases with increase of Ge concentration. This remarkable change in the behavior of the transition temperatures is discussed in terms of the Mn-Mn distance and ascribed to a change in the exchange constant Jex.

In the present work, an experimental and theoretical study of the hyperfine interactions at Gd and In sites in GdIn3 were performed. The experimental measurements were carried out by perturbed angular correlation spectroscopy using 140Ce and 111Cd nuclear probes substituting Gd and In sites, respectively. Results for 111Cd probe at In sites in GdIn3 revealed only electric quadrupole interactions, differently from the results for CeIn3 where, in addition to quadrupole interactions, a magnetic hyperfine field (Bhf) was also observed at In sites. The temperature dependence of Bhf at 140Ce on Gd sites in GdIn3 could be fitted by a Brillouin curve, and the extrapolated Bhf value to 0 K was found to be much smaller than that at 140Ce in CeIn3. Ab-initio electronic structure calculations for GdIn3 matrix doped with Ce were confronted with experimental data in order to explain such differences. The calculations were carried out within density functional theory using Augmented Plane Waves plus local orbitals basis...

The magnetic and electric hyperfine interactions of the nuclear probe Cd111 in the hexagonal antiferromagnetic rare earth-gallium RGa2 (R = Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, and Er) intermetallic compounds have been investigated by perturbed angular correlation (PAC) spectroscopy as a function of temperature. With the exception of R = Nd and Ho, the magnetic hyperfine field Bhf is roughly proportional to the spin projection (g − 1)J of the R constituent. However, in the group of the light rare earths, the variation of Bhf with (g − 1)J is much weaker than that for the heavy R constituents, in contrast to the trend reported for all rare earth intermetallics investigated up to now as well as to the trend of the magnetic ordering temperatures of RGa2. The orientation of the 4f spins relative to the c axis of RGa2 deduced from the angle between Bhf and the symmetry axis of the electric field gradient was found to be temperature independent and in agreement with the results of previous magnetization measurements...

The effect of substitution of Ge for Si in LaMn2Si2 compound on the magnetic hyperfine field (Bhf) has been investigated by perturbed γ−γ angular correlation (PAC) spectroscopy using 140La(140Ce) as probe nuclei. This compound exhibits antiferromagnetism followed by a ferromagnetic ordering when temperature decreases. The behavior of the ferromagnetic transition when Ge gradually replaces Si, with concentrations of 20%, 40%, 80%, and 100% is discussed. PAC measurements were carried out in the temperature range from 15 K to 325 K. Results for LaMn2Si2 compound showed that the dependence of Bhf with temperature follows the expected behavior for the host magnetization and could be fitted by a Brillouin function for JMn = 5/2. However, the temperature dependence of Bhf for compounds when Si is gradually replaced by Ge showed a deviation from such a behavior, which gradually increases up to a strong deviation observed for LaMn2Ge2. This striking behavior was ascribed to the hybridization of d band of the host and f band of the Ce impurities, which is stronger when the unit cell volume increase as Si ions are substituted by Ge atoms.

The magnetic hyperfine field (Bhf) in RZn compounds (R = Gd, Tb, Dy) has been investigated by perturbed angular correlation spectroscopy using 140Ce and 111Cd as probe nuclei, respectively, at R and Zn sites, in order to study the origin of the magnetic coupling in these compounds. The results for 111Cd probe showed that the temperature dependence of Bhf roughly follows the Brillouin function for the R total angular momentum J of each compound. The temperature dependence of Bhf measured with 140Ce probes showed, however, a sharp deviation from the Brillouin curve for all compounds, which was ascribed to the contribution of the 4f-electron of Ce3+ to Bhf.

A study of the magnetic, electrical resistivity and hyperfine properties of polycrystalline La2RuO5 compounds is presented in this work. This compound forms in a monoclinic phase (space group P21/c). Magnetic susceptibility measurements yield an effective magnetic moment which is consistent with spin S = 1 of Ru ions, and a negative paramagnetic Curie temperature which indicates the presence of antiferromagnetic interactions. Below T ∼ 165 K, the magnetization shows a sudden decrease, precisely where the electrical resistivity shows a change in the activation energy. Room-temperature perturbed angular correlation spectrum is well fitted considering two electric-quadrupole components. The temperature dependences of electric-quadrupole frequencies and asymmetry parameters corroborate the occurrence of a phase transition at T ∼ 170 K. Moreover, below 170 K, magnetic-dipole interactions, which coexist with electric-quadrupole interactions, are observed at Ru sites. This is considered as a strong evidence for ...

Hyperfine interactions in perovskite-structure RCoO3 (R=Gd,Tb) compounds have been measured by perturbed angular correlation technique using Cd111 and Ta181 nuclear probes. The electric quadrupole interactions at Cd111 show two different sites, assigned to probe substituting Gd or Tb and Co atoms. The temperature dependence of quadrupole frequencies shows discontinuities which have been interpreted as thermally activated spin-state transitions from low-spin ground state configuration to the intermediate-spin (IS) state and from IS state to high-spin state of Co3+ ion. For Ta181 only one major interaction was observed, which was assigned to probe at Co sites. Indication of a Jahn-Teller distortion, which stabilizes the intermediate-spin state with orbital ordering, is also pointed out.

The local magnetism at R and In sites in RNiIn (R=Gd, Tb, Dy, Ho) compounds was investigated by measuring hyperfine interactions via perturbed gamma-gamma angular correlation (PAC) technique using La140–Ce140 and In111–Cd111 probe nuclei. PAC measurements carried out below respective TC for each compound showed a combined electric quadrupole plus magnetic dipole interaction for Cd111 probe at In sites and a pure magnetic interaction for Ce140 at R sites. The temperature dependence of the magnetic hyperfine field (Bhf) shows that, whereas the Bhf values at rare-earth sites measured with Ce140 drop to zero at temperatures around the expected TC for each compound, the respective fields at In sites measured with Cd111 drop to zero at lower temperatures. The difference between the temperatures at which Bhf is zero for Ce140 and Cd111 probes when compared with TC of each compound shows that this difference decreases with decreasing TC values. The results are discussed in terms of the Ruderman-Kittel-Kasuya-Yosi...

A local study of the influence of annealing temperature that can provoke structural defects and chemical disorder on the magnetism of Heusler alloys has been carried out by measuring hyperfine interactions in Pd2MnZ (Z=Ge, In, Sn, and Sb). Perturbed angular correlation method has been used to measure the hyperfine fields at Cd111 probe nuclei substituting the Mn and Z sites as a function of temperature. The fraction of In111-nuclei-occupying Mn sites was found to increase with the annealing of sample at higher temperatures followed by quenching that can leave the alloy in a disordered state. As a consequence, it was possible to observe the effect of temperature in the ordering of the alloys. Moreover, electric quadrupole interaction measurements clearly indicated chemical disorder after quenching in Pd2MnSn and an improvement in the ordering of the Pd2MnGe structure at high temperatures.

Time differential perturbed angular correlation (TDPAC) measurements were carried-out on PbZr0.8Ti0.2 O3 as a function of temperature. A broad distribution of electric field gradient (EFG) was observed in all cases with a second site for 181Hf-181 Ta probes in the R3c phase. The results were analyzed in terms of a model which simulates an attraction of the ions by the smaller Ti ions. The EFG was calculated within the point charge approximation, by averaging over a large number of configurations generated by random distribution of the Ti ions in an ensemble of lattice cells. It was verified that the model reproduces qualitatively the broadening of the TDPAC frequencies as well as explains the second component EFG observed experimentally.