Hyperfine Fields Of Impurities Research Articles

First principles density functional calculation of magnetic moment and hyperfine fields of dilute transition metal impurities in Gd host

We present first principles calculations of electronic structure and magnetic properties of dilute transition metal (3d, 4d and 5d) impurities in a Gd host. The calculations have been performed within the density functional theory using the full potential linearized augmented plane wave technique and the GGA+U method. The spin and orbital contributions to the magnetic moment and the hyperfine fields have been computed. We find large magnetic moments for 3d (Ti–Co), 4d (Nb–Ru) and 5d (Ta–Os) impurities with magnitudes significantly different from the values estimated from earlier mean field calculation [J. Magn. Magn. Mater. 320 (2008) e446–e449]. The exchange interaction between the impurity and host Gd moments is found to be positive for early 3d elements (Sc–V) while in all other cases an anti-ferromagnetic coupling is observed. The trends for the magnetic moment and hyperfine field of d-impurities in Gd show qualitative difference with respect to their behavior in Fe, Co and Ni. The calculated total hyperfine field, in most cases, shows excellent agreement with the experimental results. A detailed analysis of the Fermi contact hyperfine field has been made, revealing striking differences for impurities having less or more than half filled d-shell. The impurity induced perturbations in host moments and the change in the global magnetization of the unit cell have also been computed. The variation within each of the d-series is found to correlate with the d–d hybridization strength between the impurity and host atoms.

Electronic structure and magnetic properties of 3d impurities in antiferromagneticCr

Using the full-potential linearized augmented plane wave (FLAPW) method based on thedensity function theory (DFT) we have performed ab initio calculations of magneticproperties for dilute Cr–X alloys with 3d transition metals. We present here ourresults for the density of states, local magnetic moments and hyperfine fields. Theparamagnetic local density of states (LDOS) analyzed with the Stoner modelsuggests the occurrence of local moments for Mn, Fe, Co and Ni consistent withresults obtained from spin polarized calculations. In addition, we find a largemagnetic moment for the non-magnetic V atom in Cr. The impurity moments of Sc,Ti, V and Mn are found to be antiparallel with respect to the near neighborCr moment while, they show ferromagnetic coupling for Fe, Co, and Ni. Theobserved sign change for the exchange coupling is also reflected in our calculatedhyperfine field results. The trend observed for the variation of the impurity momentand hyperfine fields of 3d impurities in antiferromagnetic Cr show remarkablesimilarity with the results reported for ferromagnetic Fe, Co and Ni hosts. Theresults presented here would be helpful for a common understanding of localmagnetic properties of transition metal impurities in ferro and antiferromagnetichosts.

Electronic structure and magnetic properties of dilute Cr alloys with transition-metal impurities

By using full-potential linearized augmented plane wave (FLAPW) method based on the density function theory (DFT), we have performed ab initio calculations of electronic structure and magnetic properties for dilute alloys of Cr with transition metals. Here, we present our results for the local magnetic properties of $3d$ (Sc\char21{}Ni) and $4d$ (Y\char21{}Pd) impurities in Cr, as well as changes in macroscopic properties such as total magnetization and specific heat of Cr alloys, arising from impurity-induced host perturbations. Results obtained for nonmagnetic local density of states is analyzed within Stoner model, and the condition for local moment formation is found to be satisfied only for Fe, Co, and Ni. For all other cases including Mn, the impurity moments are predicted to be induced by Cr host. Systematic trends for the impurity local moments and hyperfine fields in antiferromagnetic Cr host have been established. The trends show remarkable similarity with those observed in ferromagnetic Fe, Co, and Ni hosts. While the impurity moments for Sc, Ti, V, and Mn are found to be antiparallel with respect to the near neighbor Cr moment, self-consistent solutions for Fe, Co, and Ni show ferromagnetic coupling. For $4d$ impurities, except for Rh and Pd, the exchange interaction remain antiferromagnetic. The calculated changes of the total moment due to host perturbations show qualitative agreements with data from magnetization measurements. A detailed comparison is made for the impurity-induced changes in the total density of states at Fermi energy ${E}_{F}$ and experimentally measured electronic specific heat of Cr alloys. The results presented in this work provide comprehensive and improved understanding of electronic and magnetic properties of dilute Cr alloys. They are also useful for a common understanding of local magnetic properties of transition metal impurities in ferromagnetic and antiferromagnetic hosts.

Local magnetic moments and hyperfine fields of transition element impurities in ferromagnetic Gd and Tb rare earth metals

We discuss the formation of the local magnetic moments and the related magnetic hyperfine fields at nd ( n = 3 , 4 , 5 ) transition impurities diluted in ferromagnetic Gd and Tb metals. The nd impurities are described within the Wolff–Clogston picture and the mean field approximation is adopted to deal with the Coulomb-like interaction. The next-neighbor tunneling, due to the translational invariance breaking introduced by the impurity, is also included in this work. Following a self-consistent procedure and using a criterious physical choice of parameters, we are able to calculate the local magnetization and magnetic hyperfine fields at the impurity sites. The calculated hyperfine fields are in good agreement with the experiments.

Hyperfine Fields of Light Interstitial Impurities in Ni

The magnetic hyperfine interaction of light interstitial impurities in Ni have been studied by means of the Korringa-Kohn-Rostoker (KKR) band structure method. This method allows to deal with the impurity problem by solving the corresponding Dyson equation for the Green’s function. It also allows to account for lattice relaxations. For this purpose a new technique was developed that allows to handle in principle arbitrary lattice distortions. Corresponding calculations have been performed for the magnetic hyperfine fields of the light interstitial impurities H to Ne in Ni. By minimising the force on the nearest neighbour host atoms their equilibrium position was determined. The resulting hyperfine fields for the equilibrium configuration are found to be in rather good agreement with available experimental data.

Calculated hyperfine fields of 3d and 4d impurities in Co HCP

We present first-principles calculations of the hyperfine fields and magnetic moments of 3d and 4d impurities in cobalt HCP host. The first-principles discrete variational method in the self-consistent charge approximation is employed to obtain the electronic structure in spin-polarized calculations within the framework of the local approximation of the density-functional theory. Good agreement with experimental results is obtained for the calculated hyperfine magnetic fields. In the 3d series, the Cr atom has the largest value for the magnetic moment after Co, and is antiferromagnetically coupled with the surrounding host atoms. For the 4d impurities, the largest moment belongs to Rh, which is coupled in parallely to the host atomic moments.

Hyperfine fields at 3d impurities in ZrFe2 intermetallic compound: A theoretical study

In this article we study the systematics of the local magnetic moments and hyperfine fields of 3d impurities diluted in ZrFe2 intermetallic compound. In order to describe the magnetic properties of this intermetallic, we use a two coupled sublattice Hubbard Hamiltonian, treated in the mean field approximation. We include in the hopping the next neighbor perturbation, due to the transnational invariance breaking introduced by the 3d impurity. After determining the local charge potential by using an extended Friedel sum rule, we obtain the perturbed density of states and the local magnetic moments at the impurity site. The corresponding hyperfine fields are in good agreement with experimental data.

First Principles Calculation of Hyperfine Fields of Li Impurities in Ferromagnetic Nickel

The hyperfine fields of Li impurities in ferromagnetic Ni are calculated by use of the Korringa-Kohn-Rostoker (KKR) Green's function method in the framework of the local spin density approximation (LSDA) and the supercell method. The electronic structure is self-consistently determined by taking account of the local lattice relaxation around the Li impurities. The calculated hyperfine field of Li at the substitutional site shows a good agreement with the experimentally observed hyperfine field. The local lattice relaxation gives rise to fairly large configurational changes in the surrounding host atoms in the case of the interstitial Li impurities, which in turn causes remarkable changes in the hyperfine fields at the Li nucleus. This indicates that it is crucial to take the local lattice relaxation into account for the light interstitial impurities in Ni.

Effect of lattice relaxations on the hyperfine fields of heavy impurities in Fe

We present first-principles calculations of hyperfine fields of heavy impurities in BCC Fe. In particular, the effect of lattice relaxations on the calculated hyperfine fields are studied. The calculations are based on a full-potential Korringa–Kohn–Rostoker Green's function method for defects and employ the local spin–density approximation for the exchange and correlation effects. The non-spherical parts of the potential and the charge density are treated correctly, while the forces are calculated by an ionic version of the Hellmann–Feynman theorem. Lattice statics methods are used to describe the longer ranged relaxations. The calculated hyperfine fields of 5sp and 6sp elements are compared with the available experimental data and it is shown that the inclusion of lattice relaxations in the calculation improves the agreement with experiments.

Lattice relaxations and hyperfine fields of heavy impurities in Fe

We present first-principles calculations of the lattice relaxations and hyperfine fields of heavy impurities in bcc Fe. We consider impurities of the $5sp$ and $6sp$ series, containing the largest atoms in the periodic table. As an application we calculate the hyperfine fields of these impurities and in particular the effects of lattice relaxations on these fields. The calculations are based on a full-potential Korringa-Kohn-Rostoker Green's-function method for defects and employ the local spin-density approximation for the exchange and correlation effects. The nonspherical parts of the potential and the charge density are included in the calculations and the forces are calculated by an ionic version of the Hellmann-Feynman theorem. The resulting lattice relaxations are relatively small, even for the largest impurities considered. The comparison of the calculated hyperfine fields with the experimental data shows that the inclusion of lattice relaxations improves the overall agreement with experiment.

Theoretical study of the hyperfine fields of Co impurities in Mo hosts

The currently accepted measured value for the hyperfine field at a Co impurity in Mo hosts is -2.6 T. Contrary to this value, in a previous work we have calculated the Fermi contact contribution to the hyperfine field at an isolated Co impurity in Mo hosts using the RS-LMTO-ASA scheme and we have found the value -8.9 T. In order to investigate if this discrepancy is due to the formation of small Co clusters in the measured sample, here we study, theoretically, the behaviour of local magnetic moments and hyperfine fields in three systems, representing different local configurations of Co atoms in Mo hosts: Co sites at Co dimmers; Co with a nearest neighbour vacancy; and a 9 Co atoms cluster. In all cases we use the RS-LMTO-ASA scheme. Our results suggest that the hyperfine fields at Co atoms in Mo can be very sensitive to the homogeneity of the alloy.

Hyperfine fields of probe atoms on the (001) surface of Ni

Abstract We present first-principles calculations of the electronic structure and hyperfine fields of 3d and 4sp impurities on the (001) surface of Ni. The calculations are based on the local-spin-density-functional theory and employ a Korringa-Kohn-Rostoker Green's function method for impurities at surfwes. The systematic behaviour obtained for the hyperfine fields of the 4sp adatoms or impurities in the first surface layer is completely different from that found in the bulk. Instead of a single maximum with a very large hyperfine-field value at about the end of an sp series, the adatoms exhibit two maxima with a pronounced minimum in between. This behaviour can be traced back to the reduced coordination number of the adatoms which leads to a much smaller relative splitting of the bonding and antibonding peaks, and to the lower symmetry at the surface which results in an on-site s-p: hybridization. The hyperfine fields found for the 3d impurities at the surface are determined basically by the ferromagnet...

Temperature anomaly of the Cd hyperfine field in a trivacancy complex in Ni

The temperature dependence of the Cd hyperfine field in a trivacancy complex in Ni between 25 and300 K is reported. It was found that, unlike the Cd substitutional field in Ni which follows the temperature dependence of the magnetization, the Cd hyperfine field in a trivacancy complex is essentially temperature independent. This temperature anomaly is compared with other temperature anomaly of impurity hyperfine fields in ferromagnetic hosts.

Green's function calculations of the hyperfine interaction for impurities in metals andfor metallic interfaces

We present local density functional calculations for magnetic impurities andmagnetic monolayers in non-magnetic metals. The calculations employ a multiple scattering (KKR) Green's function method for impurities in the bulk andfor ideal surfaces and interfaces. In particular we discuss the moment formation of 3d and4d impurities in alkali andnoble metals. Special emphasis is put on an accurate calculation of the host polarization around 3d impurities in Cu andPd. While the calculated impurity hyperfine fields in Cu contain rather large errors due to the local density approximation, the induced fields of the Cu atoms agree very well with experiments. We also present similar calculations for magnetic monolayers andthe corre-sponding induced host polarization in Cu andPd.

The hyperfine fields of light impurities in iron

The hyperfine fields of light impurities in iron

Hyperfine interactions of111Cd in ion-implanted face centered cubic cobalt

The magnetic-dipole and electric-quadrupole hyperfine interactions of111Cd probes in fcc cobalt after implantation of radioactive111In+ ions have been investigated by PAC measurements with fast BaF2 detectors. Six different sites of the probe atoms could be distinguished and characterized by their hyperfine parameters and annealing behaviour. Besides the substitutional site, three sites are assigned to In-vacancy complexes which are formed athermally in the implantation process or by thermally-activated trapping of lattice defects in annealing stage III. The remaining two sites are attributed to In located in stacking faults or hcp regions of the host. Systematic trends of impurity hyperfine fields in defect sites become evident from a comparison with other impurity-host combinations. The temperature dependence of the magnetic hyperfine fields has been measured between 20 K and 390 K. Large differences found for the various sites are discussed.

Hyperfine fields at nonmagnetic impurities in ferromagnetic GdZn and GdCd

Hyperfine fields at sp impurities in ferromagnetic CsCl type compounds GdZn and GdCd have been measured by NMR method. The impurity hyperfine fields are always negative, indicating the negative polarization of s-like conduction electrons at impurities on the Zn(Cd) sites, and are smaller at the beginning and end of each sp series. This trend of the hyperfine fields is similar to that in Gd metal and is qualitatively understood by the Daniel-Friedel mechanism.

Magnetic hyperfine fields of 5sp impurities in vacancy complexes in ferromagnetic metals

A survey is given of recent experimental results for the hyperfine interactions of 5sp impurities in vacancy complexes in ferromagnetic 3d host metals. Emphasis is put on changes of the impurity magnetic hyperfine fields in such complexes as compared to substitutional lattice sites. Systematic trends are presented, which are beginning to emerge from studies of Cd and Sn impurities in particular.

Hyperfine fields of 3d and 4d impurities in nickel.

We present detailed calculations of the electronic structure and the hyperfine fields of 3d and 4d impurities in nickel. The calculations are based on the local-density approximation of density-functional theory and the Korringa-Kohn-Rostoker Green's-function method for impurity calculations. We self-consistently calculate the local moments and hyperfine fields of the impurities and their nearest neighbors. We derive new formulas for the proper relativistic generalizations of the contact, orbital, and dipolar contributions to the hyperfine field and explicitly calculate relativistic corrections to the contact interaction which are important for 4d impurities. The hyperfine fields can be split up into local and transferred contributions which are directly related to the local moments and to the moments of the neighboring atoms. The calculated hyperfine fields are in reasonable agreement with the experimental data.

Hyperfine fields of impurities in ferromagnets

Due to the development of Green's function methods the calculation of hyperfine fields of impurities in ferromagnets has become feasible in the last years. We present the result of recent calculations for sp- and d-impurities and their nearest neighbours in Fe. The calculations are based on density functional theory; the potentials of both the impurity and the neighboring host atoms are determined self-consistently. For not too heavy impurities ( Z ≤ 50) the calculations well produce the observed trend of hyperfine fields. We discuss the strong correlation between the local magnetic moment of magnetic impurities and the hyperfine field, observed experimentally, in the light of the calculations. For sp-impurities the so-called systematic behavior of the hyperfine field with increasing Z is explained in terms of the bonding properties between impurity s and host d orbitals.