Magnetic Hyperfine Interaction Research Articles

Synthesis and Local Characterization of CoO Nanoparticles in Distinct Phases: Unveiling Polymorphic Structures.

The advancement of functional nanomaterials has become a major focus of recent research, driven by the exceptional properties these materials display compared to their macroscopic (bulk) counterparts. Cobalt oxide nanoparticles (CoO-NPs) stand out primarily for their catalytic and magnetic properties, which can enable a range of technological applications, such as advanced catalysts, drug delivery systems, implants, prosthetics, sensors. However, in addition to the dependence on factors such as size, morphology, and functionalization, the properties of CoO-NPs are significantly influenced by the crystal structure. Therefore, local investigation into the polymorphic structures of CoO at the nanometric scale may provide new insights into the local structural and magnetic characteristics of these systems. In this report, we address the synthesis and local characterization of cobalt oxide (CoO) nanoparticles in the rock-salt cubic fcc-CoO and Wurtzite hpc-CoO phases, obtained through thermal decomposition. We analyze the influence of oleylamine and oleic acid ligands on the structural and morphological control of these systems. The obtained nanoparticles were characterized using conventional techniques such as X-ray diffraction (XRD), transmission electron microscopy, Raman spectroscopy, and Fourier-transform infrared spectroscopy. Local characterization was carried out by the perturbed angular correlation (PAC) nuclear technique using the radioactive tracer 111In(111Cd). Measurements were conducted at 295 and 10 K to investigate possible magnetic phase transitions in these systems. XRD results confirmed the formation of fcc-CoO and hcp-CoO phases. The phase fcc was obtained with the pair of oleylamine and oleic acid ligands, while the phase hcp phase was synthesized using only oleylamine. Additionally, nanoparticles synthesized with oleylamine and oleic acid exhibited better morphological control compared to those produced with only oleylamine. Raman spectroscopy analyses suggest a phase transformation process resulting in Co3O4. PAC results for hyperfine interactions at the 111In(111Cd) probe nucleus, indicate that the hcp-CoO phase shows smaller hyperfine magnetic interactions (B hf = 1 T) compared to the fcc-CoO phase (B hf = 17 T). This suggests the mechanism of superexchange interactions, which are strongly influenced by the Co-O-Co bond angle, which is 110° for the hpc-CoO phase and 180° for the fcc-CoO phase due to the geometries of the systems.

The magnetic structure and spin-reorientation of ErGa.

The magnetic structure of the intermetallic compound ErGa has been determined using high-resolution neutron powder diffraction. This compound crystallizes in the orthorhombic (Cmcm, No. 63) CrB-type structure and orders ferromagnetically at 32 (2) K, with the Er moments initially aligned along the b axis. Upon cooling below 16 K, the Er magnetic moments cant away from the b axis towards the c axis. At 3 K, the Er moment is 8.7 (3) μB and the Er magnetic moments point in the direction 31 (3)° away from the crystallographic b axis, within the bc plane. 166Er Mössbauer spectroscopy work supports this structure and shows clear signals of the spin-reorientation in both the magnetic and electric quadrupole hyperfine interactions.

First-principle study of the ground-state crystal structure and optoelectronic response of CsPbX3 (X= Cl, Br, I) for photovoltaic applications

The optoelectronic response and ground state crystal structure of tetragonal (P4/mbm), orthorhombic (Pmnb) and monoclinic (P21/m) phases of CsPbX3 (X = Cl, Br, I) are studied for optoelectronic applications using first principle simulations. Electric field gradient (EFG) and magnetic hyperfine interactions are investigated to explore the charge distributions surrounding the nucleus and local magnetic environment of the atomic nucleus. The orthorhombic phase of these compounds is more stable having lowest ground-state energy compared to tetragonal and monoclinic phases. The understudied halide perovskites have direct band gap nature and spin orbit coupling (SOC) effect splits Pb-p and X-p orbitals at the edges of conduction and valence band (CB and VB) respectively. At the edge of VB, the strongly hybridized X-p and Pb-p orbital and direct band gap nature of CsPbX3 is excellent for the light absorption and photovoltaic (PV) applications. The n-i-p configuration (FTO/ETL/CsPbX3/HTL/Au) of the simulated structure shows that CsPbI3 has improved power conversion efficiency (PCE) of 22.48 % and 22.32 % and quantum efficiency (QE) about ∼80 % in tetragonal and monoclinic phases respectively. The Pb and Cs values of EFG tensor in z-direction (Vzz) are close to each other, which show that the distribution of electronic charge density is similar near these nuclei. Moreover, Cs-s orbital has negligible contribution and Pb-p and I-p orbitals have higher contribution in the hyperfine field (HFF). The negative HFF indicates the opposite HFF contribution.

Hyperfine interactions for small systems including transition-metal elements using self-interaction corrected density-functional theory

The interactions between the electronic magnetic moment and the nuclear spin moment, i.e., magnetic hyperfine (HF) interactions, play an important role in understanding electronic properties of magnetic systems and in realizing platforms for quantum information science applications. We investigate the HF interactions for atomic systems and small molecules, including Ti or Mn, by using Fermi–Löwdin orbital (FLO) based self-interaction corrected (SIC) density-functional theory. We calculate the Fermi contact (FC) and spin-dipole terms for the systems within the local density approximation (LDA) in the FLO-SIC method and compare them with the corresponding values without SIC within the LDA and generalized-gradient approximation (GGA), as well as experimental data. For the moderately heavy atomic systems (atomic number Z ≤ 25), we find that the mean absolute error of the FLO-SIC FC term is about 27 MHz (percentage error is 6.4%), while that of the LDA and GGA results is almost double that. Therefore, in this case, the FLO-SIC results are in better agreement with the experimental data. For the non-transition-metal molecules, the FLO-SIC FC term has the mean absolute error of 68 MHz, which is comparable to both the LDA and GGA results without SIC. For the seven transition-metal-based molecules, the FLO-SIC mean absolute error is 59 MHz, whereas the corresponding LDA and GGA errors are 101 and 82 MHz, respectively. Therefore, for the transition-metal-based molecules, the FLO-SIC FC term agrees better with experiment than the LDA and GGA results. We observe that the FC term from the FLO-SIC calculation is not necessarily larger than that from the LDA or GGA for all the considered systems due to the core spin polarization, in contrast to the expectation that SIC would increase the spin density near atomic nuclei, leading to larger FC terms.

Relativistic Douglas–Kroll–Hess calculations of hyperfine interactions within first-principles multireference methods

A relativistic magnetic hyperfine interaction Hamiltonian based on the Douglas–Kroll–Hess (DKH) theory up to the second order is implemented within the ab initio multireference methods, including spin–orbit coupling in the Molcas/OpenMolcas package. This implementation is applied to calculate relativistic hyperfine coupling (HFC) parameters for atomic systems and diatomic radicals with valence s or d orbitals by systematically varying active space size in the restricted active space self-consistent field formalism with restricted active space state interaction for spin–orbit coupling. The DKH relativistic treatment of the hyperfine interaction reduces the Fermi contact contribution to the HFC due to the presence of kinetic factors that regularize the singularity of the Dirac delta function in the nonrelativistic Fermi contact operator. This effect is more prominent for heavier nuclei. As the active space size increases, the relativistic correction of the Fermi contact contribution converges well to the experimental data for light and moderately heavy nuclei. The relativistic correction, however, does not significantly affect the spin-dipole contribution to the hyperfine interaction. In addition to the atomic and molecular systems, the implementation is applied to calculate the relativistic HFC parameters for large trivalent and divalent Tb-based single-molecule magnets (SMMs), such as Tb(III)Pc2 and Tb(II)(CpiPr5)2 without ligand truncation using well-converged basis sets. In particular, for the divalent SMM, which has an unpaired valence 6s/5d hybrid orbital, the relativistic treatment of HFC is crucial for a proper description of the Fermi contact contribution. Even with the relativistic hyperfine Hamiltonian, the divalent SMM is shown to exhibit strong tunability of HFC via an external electric field (i.e., strong hyperfine Stark effect).

Magnetic hyperfine interactions of probe 57Fe atoms within the hexagonal manganite ScMnO3

Here we present the Mössbauer study of the combined magnetic and electrical hyperfine interactions of the probe 57Fe nuclei localized in the hexagonal manganite ScMnO3. The hyperfine interactions were measured in the temperature range where ScMnO3 demonstrates spin ordering: 15 K <T <TN (∼ 130 K). By analyzing the hyperfine parameters of 57Fe nuclei, we evaluated the oxidation state of the iron ions, their local crystal environment, and the orientation of the magnetic moments μFe in the structure of ScMn0.99657Fe0.004O3 at T <<TN. The temperature-dependent evolution of Zeeman structures in Mössbauer spectra was analyzed using the stochastic relaxation model, and indicates the presence of frustration of the superexchange interactions Fe3+−O−Mn3+. The temperature dependence of the hyperfine magnetic field Bhf(T) was described using critical indices, whose values reflect the reduced dimensionality of the magnetic system under study. It was shown that the observed sharp temperature-dependent change of the quadrupole shift of the Zeeman structure components may be attributed to the spin reorientation process, resulting in antiferromagnetism with a weak ferromagnetic component.

Magnetic ground states and hyperfine interactions in YMnO[formula omitted] using density functional theory

This study employs the Local Density functional theory (DFT) and the DFT+U extension, to better describe the localized d-Mn states, and therefore analyze six magnetic configurations of the Mn ions in hexagonal manganite YMnO3. The respective study was complemented through hyperfine interaction calculations of different atomic configurations. Our focus is on six distinct magnetic configurations, complemented by thorough Hyperfine Interactions (HFI) calculations targeting the most plausible configuration. We find the P6’3 and P63 configurations are the most probable, aligning with previous research in the field. These configurations also show a strong correlation with experimental observations of magnetic moments, providing new insights into the magnetic ordering of YMnO3. Our results highlight the intricate relationship between magnetic moments and the lattice structure of YMnO3, offering valuable insights into the material’s magnetic properties.

Magnetic hyperfine interaction made easier

We present two derivations of the hyperfine interaction in the ground state of hydrogen using classical electrodynamics. We calculate, at the site of the proton moment m→p, the magnetic field B→e due to the magnetization source M→e(r→) of the relatively extended 1 s electron state. This gives the magnetic interaction via −m→p·B→e. One derivation applies the Biot–Savart law to the bound 1 s electric current J→b=∇→×M→ to directly find B→e; the other derivation applies the magnetic version of the Coulomb Law to the bound 1 s magnetic charge density ρb=−∇→·M→ to first obtain μ0H→e and then adds μ0M→ to find B→e. We show, for any source M→, that these two approaches give the same B→(r→), as is expected within classical electrodynamics.

Temperature-dependent evolution of micromagnetic structure of B20-type Fe1-xCoxGe studied by Mössbauer spectroscopy

The non-collinear magnetic structures hosted in magnets with broken central inversion symmetry, some of which are topologically non-trivial, have unique physical properties and application prospects. This paper presents a detailed study of the temperature evolution of the micromagnetic structures of B20-type Fe1-xCoxGe (x = 0, 0.05, 0.10) polycrystalline samples using 57Fe Mössbauer spectroscopy. We take the relatively weak electric quadrupole interaction as a perturbation of the hyperfine magnetic interaction to obtain the distribution of the hyperfine magnetic field Hhf (φ) in the plane perpendicular to the magnetic propagation vector ks. It is found that the geometric features of Hhf (φ) are sensitive to the relative orientation of ks regarding the electric field gradient at the iron nucleus, as well as to the spin texture. The temperature dependence of Hhf (φ) provides a distinct signal of first-order phase transition when ks shifts from [100] to [111]. The doping of cobalt atoms leads to out-of-plane component and in-plane component aggregation of the neighboring iron magnetic moments. These results are instructive for understanding the dynamical behavior of spiral magnets with long-periods.

Understanding Complex Interplay among Different Instabilities in Multiferroic BiMn7O12 Using 57Fe Probe Mössbauer Spectroscopy.

Here, we report the results of a Mössbauer study on hyperfine electrical and magnetic interactions in quadruple perovskite BiMn7O12 doped with 57Fe probes. Measurements were performed in the temperature range of 10 K < T < 670 K, wherein BiMn6.9657Fe0.04O12 undergoes a cascade of structural (T1 ≈ 590 K, T2 ≈ 442 K, and T3 ≈ 240 K) and magnetic (TN1 ≈ 57 K, TN2 ≈ 50 K, and TN3 ≈ 24 K) phase transitions. The analysis of the electric field gradient (EFG) parameters, including the dipole contribution from Bi3+ ions, confirmed the presence of the local dipole moments pBi, which are randomly oriented in the paraelectric cubic phase (T > T1). The unusual behavior of the parameters of hyperfine interactions between T1 and T2 was attributed to the dynamic Jahn-Teller effect that leads to the softening of the orbital mode of Mn3+ ions. The parameters of the hyperfine interactions of 57Fe in the phases with non-zero spontaneous electrical polarization (Ps), including the P1 ↔ Im transition at T3, were analyzed. On the basis of the structural data and the quadrupole splitting Δ(T) derived from the 57Fe Mössbauer spectra, the algorithm, based on the Born effective charge model, is proposed to describe Ps(T) dependence. The Ps(T) dependence around the Im ↔ I2/m phase transition at T2 is analyzed using the effective field approach. Possible reasons for the complex relaxation behavior of the spectra in the magnetically ordered states (T < TN1) are also discussed.

57Fe Mössbauer Effect Study of Y(Fe1 – xNix)2 Synthesized under High Pressure

The measurements of magnetic hyperfine fields (MHF), Hhf, and isomer shift, δ, in Y(Fe1 – xNix)2 intermetallic compounds (the MgCu2 structure type) synthesized at high pressure are performed. The MHF values that appear on 57Fe nuclei at a nickel concentration x below 20 at % practically do not change and are approximately equal to 22 T, and in the range from x = 0.4 to 0.98 they decrease linearly with an increase in the Ni concentration. However, linear extrapolation of the hyperfine field as a function of Ni concentration does not lead to its disappearance in YNi2. For YFe2, the rotation of the easy axis from the [101] direction to the [111] direction with increasing temperature is found. As the Ni concentration increases to x = 0.3 at a temperature of 5 K, the easy magnetization axis [101] is observed, and at x = 0.4 the axis changes direction to [100]. Based on the shape of the concentration dependence of the hyperfine field, it is assumed that during the crystallization of Y(Fe1 – xNix)2 under high pressure conditions, a magnetic moment exists on Ni ions. First-principles calculations of magnetic properties and hyperfine interactions are performed, which are consistent with experiment.

Fourier-transform microwave spectroscopy of the s-trans-3-propenalyl (CH2CHĊO) and 3-propenolyl (ĊH2CHCO) radicals.

Pure rotational transitions of two conformers of the CH2CHCO radical have been observed by Fourier-transform microwave spectroscopy, where one conformer is called the s-trans-3-propenalyl radical and the other the 3-propenolyl radical. The observed two conformers have different electronic states. The former, the s-trans-3-propenalyl radical, has the 2A' electronic state and can be written as CH2CHĊO, where the unpaired electron resides mainly on the terminal CO carbon. On the other hand, the latter, 3-propenolyl radical has the 2A'' electronic state and can be written as ĊH2CHCO. We were able to observe pure rotational transitions of the two conformers. Since both of the species have an unpaired electron, there exist spin-rotation interactions due to the unpaired electron and the magnetic hyperfine interactions due to the three coupling protons. The observed very complicated spectra, caused by these interactions, were assigned, leading to detailed molecular constants including the fine and hyperfine coupling constants for both of the species. The determined molecular constants support the electronic structures of the two conformers. There exists a controversy as to which of the two conformers is the lowest energy one. Our present observation led to the conclusion that s-trans-3-propenalyl is the lowest energy conformer.

Re-Evaluation of the Nuclear Magnetic Octupole Moment of 209Bi

We modified the Hfs92 code of the GRASP package in order to describe the magnetic octupole hyperfine interaction. To illustrate the utility of the modified code, we carried out state-of-the-art calculations of the electronic factors of the magnetic octupole hyperfine interaction constants for levels in the ground configuration of the Bi atom. The nuclear magnetic octupole moment of the 209Bi isotope was extracted by combining old measurements of the hyperfine structures of 6p34S3/2o [Hull, R.; Brink, G. Phys. Rev. A 1970, 1, 685] and 2P3/2o [Landman, D.A.; Lurio, A. Phys. Rev. A 1970, 1, 1330] using the atomic-beam magnetic-resonance technique with our theoretical electronic factors. The present extracted octupole moment was consistent with all the available values but the one obtained in the single-particle nuclear shell model approximation. This observation supports the previous finding that nuclear many-body effects, such as the core polarization, significantly contribute to the nuclear magnetic octupole moment in the case of 209Bi.

Hyperfine structure studies of neutral praseodymium with Fourier transform spectroscopy

The hyperfine structure patterns of some neutral praseodymium (Pr I) lines in the range of 2969 − 34998 cm−1 were investigated based on the archival data from the Fourier transform spectrometer at the US National Solar Observatory. The hyperfine magnetic dipole interaction constants A are presented by fitting the spectra with our spectral analysis program. The HFS constants A for 56 levels of Pr I from 0.0 to 27602.42 cm−1 were determined.

Ab initio calculations of the hyperfine structure of 109Cd, 109Cd+ and reevaluation of the nuclear quadrupole moment Q(109Cd)

Large scale ab initio calculations of the electric contribution (i.e. the electric field gradient (EFG)) to the electric quadrupole hyperfine interaction constants B for the state of 109Cd+ ion and the states of neutral 109Cd atom were performed. To probe the sensitivity of B to different electron correlation effects, six sets of variational multi-configuration Dirac–Hartree–Fock and relativistic configuration interaction calculations employing different strategies were carried out. The calculated EFGs, together with experimental values of B, allow us to extract a new value of the nuclear electric quadrupole moment Q(109Cd) = 0.634(22) b which is about 5% larger than the recommended value (Stone 2016 At. Data Nucl. Data Tables 111–112 1; Pyykkö 2018 Mol. Phys. 116 1328). Efforts were made to provide a realistic theoretical uncertainty for the final Q value based on statistical principles and correlation with the magnetic dipole hyperfine interaction constant A.

Temperature dependence and intermediate valence on magnetic hyperfine field at a Ce impurity diluted in RZn

In this work, we theoretically study the influence, at finite temperature, of the intermediate valence on the local moment formation and the magnetic hyperfine field at a Ce impurity diluted in RZn (R = Gd, Tb, Dy). The temperature dependence of the local magnetic moments and related hyperfine magnetic interaction is calculated by a functional integral approach in the static approximation, thereby extracting the 4f Ce valence at the range of temperature T ≤ TC (TC = critical temperature). Our self-consistent calculation shows that the intermediate valence model, focusing on the temperature dependence, explains the experimentally observed magnetic hyperfine fields at Ce impurity in these compounds, in particular exhibiting the two regimes of the magnetic hyperfine fields (and local magnetic moments) with temperature.

Functional integral approach for temperature dependence of the magnetic hyperfine field at a Cd site in RCd (R = Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho and Er)

A theoretical study of the local moment formation and of the magnetic hyperfine field at a non-magnetic s-p site, namely Cd, embedded in RCd (R = Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho and Er) compounds is reported. The functional integral approach in the static approximation is adopted to calculate the temperature dependence of the local magnetic moments and hyperfine magnetic interactions, which is an extension of conventional mean field approach. Our calculations are performed in the temperature range from T=0K up to the critical temperatures TC of each compound, when they become paramagnetic. The local magnetic moments at a Cd, as a function of the temperature, were calculated from the perturbed densities of states. The results of our self-consistent calculations for the magnetic hyperfine field at the impurity site are in very good agreement with recent experimental reports. Furthermore, at T=0 K our results are compared with those obtained from ab initio calculations.

Benchmarking of the Fock-space coupled-cluster method and uncertainty estimation: Magnetic hyperfine interaction in the excited state of BaF

We present an investigation of the performance of the relativistic multi-reference Fock-space coupled cluster (FSCC) method for predicting molecular hyperfine structure (HFS) constants, including a thorough computational study to estimate the associated uncertainties. In particular, we considered the $^{19}$F HFS constant in the ground and excited states of BaF. Due to a larger basis set dependence, the uncertainties on the excited state results (16-85%) were found to be significantly larger than those on the ground state constants ($\sim$2%). The ab initio values were compared to the recent experimental results, and good overall agreement within the theoretical uncertainties was found. This work demonstrates the predictive power of the FSCC method and the reliability of the established uncertainty estimates, which can be crucial in cases where the calculated property cannot be directly compared to experiment.

Hyperfine Structure Constants of Sc i and Sc ii with Fourier Transform Spectroscopy

Abstract We report new experimental hyperfine structure (HFS) constants of neutral and singly ionized scandium (Sc i and Sc ii). We observed spectra of Sc–Ar and Sc–Ne hollow cathode discharges in the region 200–2500 nm (50,000–4000 cm−1) using Fourier transform spectrometers. The measurements show significant HFS patterns in 1431 spectral lines fitted in our 12 spectra given in Table 1. These were fitted using the computer package Xgremlin to determine the magnetic dipole hyperfine interaction constant (A) for 185 levels in Sc i and 6 levels in Sc ii, of which 80 Sc i levels had no previous measurements. The uncertainty in the HFS A constant is between 1 × 10−4 and 5 × 10−4 cm−1.

The [formula omitted] state of KCs revisited: Hyperfine structure analysis and potential refinement

Laser-induced fluorescence spectra of the c3Σ+(vc,Jc=Nc)→a3Σ+(va,Na=Jc±1) transitions excited from the ground X1Σ+ state of 39K133Cs molecule were recorded with Fourier-transform spectrometer IFS125-HR (Bruker) at the highest achievable spectral resolution of 0.0063 cm−1. Systematic study of the hyperfine structure (HFS) of the a3Σ+ state for levels with va∈[0,27] and Na∈[24,90] shows that the splitting monotonically increases with va. The spectroscopic study was supported by ab initio calculations of the magnetic hyperfine interaction in X1Σ+ and a3Σ+ states. The discovered variation of the electronic matrix elements with the internuclear distance R is in a good agreement with the observed va-dependencies of the HFS. Overall set of available experimental data on the a3Σ+ state was used to improve the potential energy curve particularly near a bottom, providing the refined dissociation energy De=267.21(1) cm−1. The ab initio HFS matrix elements, combined with the empirical X1Σ+ and a3Σ+ PECs in the framework of the invented coupled-channel deperturbation model, reproduce the experimental term values of both ground states within 0.003 cm−1 accuracy up to their common dissociation limit.