Magnetic Hyperfine Field Bhf Research Articles

Magnetic Phase Transitions in Ultrathin YFeO3 Films According to Synchrotron Mössbauer Reflectometry Data

The magnetic properties of ultrathin single-crystal Y57FeO3 orthoferrite films have been studied by Mössbauer reflectometry. Mössbauer spectra were measured using the ESRF synchrotron in the reflection geometry. As the temperature changes from 3.6 K to about 773 K, the splitting of the Zeeman sextet in the spectra successively decreases and, simultaneously, a quadrupole doublet appears in them, which indicates the development of a magnetic phase transition. From the temperature dependences of the magnetic hyperfine field Bhf for the main orthorhombic Y57FeO3 phase, Néel temperatures equal to TN ≈ 593 K, 562 K, and 567 K and the critical parameter values equal to β ≈ (0.28–0.3) ± 0.02 are determined in films with thicknesses of 28, 6.5, and 4 nm, respectively. An analysis of changing the ratio of the line intensities in the Zeeman sextet with temperature makes it possible to trace the successive rotation of the direction of the antiferromagnetic axes in Y57FeO3 toward the surface plane with an increase in the temperature and a decrease in the film thickness.

Investigation of Mn-Fe magnetic interaction in mechanically alloyed Fe doped-MnAlC by 57Fe Mössbauer spectrometry

Four samples γ2-Mn40Fe0.5Al59.5, β-Mn60Fe0.5Al39.5, and ε-Mn50.5Fe0.5Al47C2, τ-Mn50.5Fe0.5Al47C2 were synthesized by mechanical alloying method. X-ray diffraction results showed high purity of the γ2, β, ε, and τ phases in each sample. Mössbauer measurement at room temperature showed non-ferromagnetic characteristic of the γ2-Mn40Fe0.5Al59.5, β-Mn60Fe0.5Al39.5, and ε-Mn50.5Fe0.5Al47C2. Interestingly, τ-Mn50.5Fe0.5Al47C2 showed a complex magnetic hyperfine splitting, indicating magnetic ordered structure. The hyperfine interaction in τ-Mn50.5Fe0.5Al47C2 was found dependent with temperature, in which isomer shift (IS) and magnetic hyperfine field (Bhf) decreased with increasing temperature. From the IS temperature dependence curve, the Debye temperature (θD) is determined to be 422 ± 80 K. The temperature dependence of Bhf values and the thermomagnetic measurement yielded a Curie temperature (Tc) values of 560 ± 13 K and 565 ± 2 K respectively. In order to investigate the magnetic interaction between Fe and Mn atoms in τ-Mn50.5Fe0.5Al47C2, local magnetic order of τ-Mn50.5Fe0.5Al47C2 was probed by using in-field 57Fe Mössbauer spectrometry. The obtained results showed that Fe and Mn formed a non-collinear magnetic structure with magnetic moments of Fe at different sites showing different canting angles with neighboring Mn atoms.

DFT-based calculations of the magnetic hyperfine interactions at Cd sites in RCd (R = rare earth) compounds with the FP-LAPW ELK code

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.

Effect of the magnetic impurity on the charge diffusion in highly dilute Ce doped LaMnO3

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.

Influence of Cr on structural, spectroscopic and magnetic properties of CoFe2O4 grown by the wet chemical method

The Cr doped CoFe2O4 nano crystalline ceramics are synthesized using wet chemical method. The structural, morphological, functional, spectroscopic and magnetic properties of pure CoFe2O4 and Cr doped CoFe2O4 are characterized by XRD, FESEM, FTIR, Raman, Mössbauer spectroscopy and M-H hysteresis loop. The X-ray diffraction (XRD) patterns of undoped (x = 0) and doped (x≠ 0) samples reveal the formation of single phase cubic spinel structure. The lattice parameters and cation distribution between tetrahedral (A) and octahedral (B) sites of the samples (AB2O4) were obtained by Rietveld refinement of XRD patterns. The FESEM micrographs exhibit dense micro structure with small voids. The energy dispersive x-ray studies confirm the presence of Cr in CoFe2O4. The FTIR spectrum confirms that the peaks corresponding to the metal-oxygen bonds have shiftedtowards higher wavelength region. Raman spectrum exhibits broad peaks which confirm the existence of local disorder due to the inter-site cation migration between tetrahedral and octahedral sites. The Mössbauer spectroscopy reveals that the magnitude of magnetic hyperfine field of tetrahedral site (HA) and octahedral site (HB) decreases with increase in Cr doping in CoFe2O4 and that the decrease is more rapid in tetrahedral site (HA) compared to that in octahedral site (HB). And also confirm that the magnetic hyperfine fields (Bhf) are smaller relative to pure cobalt ferrite representing that super exchange interaction which is decreases as the Cr concentration increases. The magnetization studies reveal a decrease in the saturation magnetization (Ms) of CoFe2O4with increase in Cr substitution. A similar and non-monotonic variation of coercivity (Hc) and magneto crystalline anisotropy (K) suggests that Hc is mainly determined by K.

Spin ordering and hyperfine interactions in langasite-like ferrite Ba3SbFe3Si2O14: 57Fe Mössbauer reinvestigation and ESR measurements

The present work reports new analysis and reinterpretation of the 57Fe Mössbauer data for the ferrite Ba3SbFe3Si2O14 with langasite-like crystal structure. The Mössbauer measurements show a two-step magnetic ordering process. Relaxation behavior, for temperatures below TN ≈ 32 K, persisting down to T* ≈ 20 K, indicates the coexistence of the short-range ordering spin clusters within a helically ordering state. Below T*, Mössbauer spectra are consistent with a modulated helical magnetic order, where iron magnetic moments rotate within the (ab) plane with propagation vector along c axis. All experimental spectra at T < TN were analyzed assuming the modulation of hyperfine interactions and anisotropy of the magnetic hyperfine field Bhf at the 57Fe nuclei when Fe3+ magnetic moments rotate with respect to the principal axis of the EFG tensor. The broadening of the electron spin resonance lines upon approaching TN from above was explained in terms of the short-range correlations near magnetic phase transition. The present results evidence a 3D character of magnetic correlations for high-temperatures T ≥ T0, which changes for rather 2D character of magnetic correlations below T0 ≈ 60 K. Such spin dynamics in Ba3SbFe3Si2O14 probably triggered by quasi-2D crystal structure and non-trivial helical magnetic structure.

Magnetic field at Ce impurities in La sites of La0.5Ba0.5MnO3 double perovskites

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.

Cation distributions and magnetism of Al-substituted CoFe2O4 - NiFe2O4 solid solutions synthesized by sol-gel auto-combustion method

Aluminium substituted cobalt-nickel ferrite nanoparticles were synthesized by citrate gel auto-combustion method followed by annealing at 1000 °C for 1 h in air. Scanning electron micrographs of all the samples show crystalline particles of irregular morphology with a small variation in particle sizes (~ 110–160 nm). From the analysis of the X-ray diffraction results we observed that the unit cell parameter decreases linearly with increase in aluminium concentration due to the smaller ionic radius of the Al3+ ions substituting the other cations such as Co2+, Ni2+ and Fe3+ ions in the compounds. The room temperature Mössbauer spectra of the samples show Zeeman split sextet patterns corresponding to the tetrahedral (Th) and octahedral (Oh) interstitial iron (Fe3+) cations. The observed magnetic hyperfine field (Bhf) decreases with increase in Al-concentration due to the distribution of diamagnetic Al3+ in the environment of 57Fe probe atoms. The saturation magnetization measured by Vibrating Sample Magnetometer (VSM) shows a similar trend like that of Bhf. The distributions of the cations obtained from the Rietveld refinement and Mössbauer spectroscopy results indicate an increase in Fe3+(Th)/Fe3+(Oh) occupancy-ratio on increasing Al3+ concentration, and Ni2+ cations prefer the octahedral site, whereas Co2+ and Al3+ ions redistribute themselves in tetrahedral and octahedral sites, in the ratio 2:3.

Magnetic interactions at Ce impurities in REMn2Ge2 (RE = La, Ce, Pr, Nd) compounds

In the work reported in this paper, the temperature dependence of the magnetic hyperfine field (Bhf) at 140Ce nuclei replacing Pr atoms in PrMn2Ge2 compound was measured by the perturbed angular correlation technique to complete the sequence of measurements in REMn2Ge2 (RE = La, Ce, Pr, Nd). Results show an anomalous behavior different from the expected Brillouin curve. A model was used to fit the data showing that the Ce impurity contribution (Bhfimp) to Bhf is negative for NdMn2Ge2 below 210 K. The impurity contribution (Bhfimp) at 0 K for all compounds is much smaller than that for the free Ce3+, showing that the 4f band of Ce is more likely highly hybridized with 5d band of the host. Results show that direction of the localized magnetic moment at Mn atoms strongly affects the exchange interaction at Ce impurities.

Local fields at nonmagnetic impurity sites in a perovskite La 0 . 7 Ca 0 . 3 MnO 3

The magnetic hyperfine field and electric field gradient at the 111Cd( $\leftarrow ^{\mathrm {111m}}$ Cd) and 111Cd( $\leftarrow ^{\mathrm {111}}$ In) probe nuclei introduced in a perovskite manganese oxide La0.7Ca0.3MnO3 (T C ∼ 250 K) were measured for the study of the local magnetism and structure by means of time-differential perturbed angular correlation spectroscopy. In the ferromagnetic phase at 77 K, a very slight supertransferred magnetic hyperfine field (SMHF) (< 0.014 T) combined with a well-defined electric field gradient was observed at the nonmagnetic 111Cd nucleus on the La/Ca A site. This observation suggests that the large magnetic hyperfine field (B h f = 6.9 T) measured, in our previous work, at the 140Ce probe nucleus on the A site originates from the contribution of a 4f spin oriented by the SMHF from adjacent Mn ions.

Mapping the magnetic hyperfine field in GdCo5

The magnetic hyperfine field (Bhf) in ferrimagnetic GdCo5 compound has been investigated as a function of temperature by Mössbauer 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.

Magnetic behavior of La-doped Fe3O4 studied by perturbed angular correlation spectroscopy with 111Cd and 140Ce

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 exchange interaction between Fe2+ and Fe3+ ions in the two regions of NP.

The magnetic behavior of the intermetallic compound NdMn2Ge2 studied by magnetization and hyperfine interactions measurements

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 Mn sites show that the dependence of Bhf with temperature follows the expected behavior for the host magnetization associated with the magnetic ordering of Mn ions. From these results, the antiferromagnetic transition followed by a ferromagnetic ordering is clearly observed. PAC results with 140Ce probe nuclei at Nd sites, however, showed a strong deviation from the Brillouin function, which is attributed to the Ce 4f-electron contribution to Bhf.

Hyperfine field at Mn in the intermetallic compound LaMnSi2 measured by PAC using 111Cd nuclear probe

Magnetic hyperfine field at Mn site has been measured in the orthorhombic intermetallic compound LaMnSi2 with PAC spectroscopy using radioactive 111In- 111Cd nuclear probe. Samples of LaMnSi2 were prepared by melting pure metallic components in stoichiometric proportion in an arc furnace under argon atmosphere. The samples were sealed in a quartz tube under helium atmosphere, annealed at 1000 °C for 60 h and quenched in water. Samples were analyzed with X-ray diffraction method. 111In was introduced in the samples by thermal diffusion at 1000 °C for 60 h. PAC measurements were carried out with a six BaF2 detector spectrometer at several temperatures between 50 K and 410 K. Results show well defined quadrupole and magnetic interactions at all temperatures. The magnetic hyperfine field (Bhf) measured at 50 K is 7.1(1) T. The temperature dependence of Bhf follows the normal Brillouin-like behavior expected for a simple ferromagnetic ordering. The ferromagnetic transition temperature (Tc) was determined to be 401(1) K.

Magnetic behavior of LaMn2(Si(1−x)Gex)2 compounds characterized by magnetic hyperfine field measurements

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 Néel 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.

Magnetic hyperfine field in antiferromagnetic RGa2 (R = Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er) studied by perturbed angular correlation spectroscopy using Cd111

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. Except for SmGa2 where the hyperfine field shows an abrupt decrease near TN, the temperature dependence of Bhf(T) is consistent with second order phase transitions. The magnetic ordering temperatures deduced from Bhf(T) agree with magnetization and neutron diffraction results.

Study of hyperfine interactions in GdIn3

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 functions as embodied in the wien2k package and with the GGA + U approximation. The value for the Hubbard U parameter was determined for each case. Results of the calculations show that the absence of Bhf in Cd probes in GdIn3 is related with the orientation of the magnetic moments in (001) direction, whereas in CeIn3 the magnetic moments are oriented out of this direction.

Investigation of the magnetic hyperfine field at R and Zn sites in RZn (R = Gd, Tb, Dy) compounds using perturbed gamma-gamma angular correlation spectroscopy with 140Ce and 111Cd as probe nuclei

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.

Effect of Ge substitution for Si on the magnetic hyperfine field in LaMn2Si2 compound measured by perturbed angular correlation spectroscopy with 140Ce as probe nuclei

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.

Hyperfine interactions in intermetallic rare earth-gallium compounds studied by 111 Cd PAC

Magnetic and electric hyperfine interaction of the nuclear probe 111In/111Cd in intermetallic compounds of the rare earth-gallium system have been investigated by perturbed angular correlation (PAC) spectroscopy. The PAC measurements, supported by X-ray diffraction, provide evidence for a marked phase preference of 111In for hexagonal RGa2 over orthorhombic RGa and of RGa3 with the L12 structure over RGa2. In the case of SmGa2, the magnetic hyperfine field Bhf, the electric quadrupole interaction and the angle β between Bhf and the symmetry axis of the electric field gradient have been determined as a function of temperature. The angle β = 0 is consistent with the results of previous magnetization studies. Up to T ≤ 17 K the magnetic hyperfine field has a constant value of Bhf = 3.0(2) T. The rapid decrease at higher T gives the impression of a first-order transition with an order temperature of TN = 19.5 K. In the RKKY model of indirect 4f interaction the ratio TC/Bhf(0) is a measure of the coupling constant. For 111Cd:SmGa2 (TC/Bhf(0)~6.5 K/T) this ratio is significantly smaller than for the same probe in other R intermetallics (SmAl2 ~9.5 K/T, Sm2In ~13.5 K/T).