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The effect of volume expansion on the magnetic properties of Nd[sub 5]Fe[sub 17] is explored using first-principle electronic structure calculations. A volume expansion of 6% increases the magnetization by ∼6% and the average total exchange parameter by ∼34%. As a result, the Curie temperature (T[sub C]) is expected to increase from 509 to 682 K. Therefore, some nonhybridizing interstitial and substitutional impurities should produce a moderate increase in T[sub C] of Nd[sub 5]Fe[sub 17]. The possible interstitial sites are discussed. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The net Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction between well-separated spin distributions can be mapped onto a RKKY interaction between two point-like effective moments. The effective moments, which a strongly oscillating dependence on the size, shape, and orientation of the spin distribution, are discussed for a variety of microscopic and macroscopic configurations. Particular emphasis is on the relation between RKKY interactions and band-structure Heisenberg exchange constants in itinerant magnets and on two-ion anisotropy contributions to the magnetocrystalline anisotropy of rare-earth ions. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Presents information on a study which investigated the magneto-optical properties of manganese-bismuth doped with chromium. Experimental details; Results and discussion; Conclusions.

Presents a study of the electronic structure and magnetic properties of iron-rich ternary compounds. Electronic structure; Results and discussion; Conclusions.

Presents a study which reported the electronic and magnetic structure and surface reactivity for R[sub2]T[sub14]B compounds. Description of the electronic structure of R[sub2]T[sub14]B crystals; Overview of the representative Auger spectra for the Nd[sub2]Fe[sub14]B surface; Oxidation of rare-earth alloys exposed to ambient atmosphere.

Carries out the self-consistent spin-polarized electronic structure calculations to derive the magnetic properties of samarium (Sm)[sub2] iron (Fe)[sub17-x]A[subx]. Application of linear-muffin-tin-orbitals method in the atomic sphere approximation; Magnetization and site decomposed magnetic moment per atom as a function of cell volume for Sm[sub2]Fe[sub17]; Site-protected spin-polarized density of states of Sm[sub2]Fe[sub17] for various Fe sites.

Deals with a study which measured at room temperature the Fe[sup57] Mössbauer spectra of Sm[sub2]Fe[sub17-x]Al[subx]. Background to the study; Experimental procedure; Results and discussion.

Provides information on a study that examined the electronic structure and Curie temperature of YFe[sub12-x]Mo[subx]N[suby] compounds using photoelectron spectroscopy. Experimental procedure; Results and discussion on the study; Conclusions.

Examines the electronic structures of Sm[sub2]Fe[sub17]N[subx] with photoemission and spin-polarized calculations. Examples of rare-earth permanent-magnetic materials with widespread applications; Description of the samples used in the study; Information on the calculated density of states for the clean and nitrided Y[sub2]Fe[sub17] compounds.

Presents photoemission studies of cobalt- and iron-based compounds with the thorium manganese[sub 12] structure. Details of the experiment; Theory used in the study; Results and discussion.

Examines the electronic and magnetic structures of YCo[sub10]V[sub2] using self-consistent spin-polarized calculations. Basis of the self-consistent spin-polarized electronic structure calculations; List of the calculated charge transfers and magnetic moments at various sites.

Deals with a study which investigated the effect of aluminum alloying on the electronic structure and magneto-optical properties of MnBi. Background to the study; Results; Discussion.

Ferromagnet/ferroelectric interface materials have emerged as structures with strong magnetoelectric coupling that may exist due to unconventional physical mechanisms. Here we present a first-principles study of the magnetoelectric effect at the ferromagnet/ferroelectric SrRuO3/BaTiO3 (001) interface. We find that the exchange splitting of the spin-polarized band structure, and therefore the magnetization, at the interface can be altered substantially by reversal of the ferroelectric polarization in the BaTiO3. These magnetoelectric effects originate from the screening of polarization charges at the SrRuO3/BaTiO3 interface and are consistent with the Stoner model for itinerant magnetism. [ABSTRACT FROM AUTHOR]

It is predicted that magnetic anisotropy of a thin magnetic film may be affected by the polarization of a ferroelectric material. Using a Fe/BaTiO3 bilayer as a representative model and performing first-principles calculations, we demonstrate that a reversal of the electric polarization of BaTiO3 produces a sizable change in magnetic anisotropy energy of Fe films. Tailoring the magnetic anisotropy of a nanomagnet by an adjacent ferroelectric material may yield entirely new device concepts, such as electric-field controlled magnetic data storage. [ABSTRACT FROM AUTHOR]

Defects play an important role in the properties of metal oxides which are currently used as barrier layers in magnetic tunnel junctions (MTJs). We study the effect of O vacancies on the interlayer exchange coupling (IEC) and tunneling magnetoresistance (TMR) in Fe-MgO-Fe tunnel junctions. Measurements of IEC in fully epitaxial Fe-MgO-Fe(001) tunnel junctions show IEC is antiferromagnetic (AFM) for small MgO thickness but changes sign and then vanishes for large barrier thickness. First-principles calculations based on density functional theory demonstrate that the presence of neutral O vacancies (F-centers) in the MgO barrier can explain this behavior. Resonant tunneling through the F-centers makes IEC AFM for thin barriers but with increasing MgO thickness the resonance contribution to IEC is reduced resulting in the ferromagnetic (FM) coupling typical for perfect MgO barriers. First-principles calculations also show that O vacancies can affect TMR. F-centers produce occupied localized s-states and unoccupied resonant p-states in the gap of MgO. We demonstrate that F-centers affect the conductance by either resonant transmission or nonresonant scattering of tunneling electrons both causing a substantial reduction of TMR compared to the ideal case. [ABSTRACT FROM AUTHOR]

First-principles calculations based on density functional theory are used to elucidate the effect of O vacancies, forming F centers, on spin-dependent tunneling in Fe/MgO/Fe(001) magnetic tunnel junctions. O vacancies produce occupied localized s states and unoccupied resonant p states, which is consistent with available experimental data. The authors find that O vacancies affect the conductance by nonresonant scattering of tunneling electrons causing a substantial reduction of tunneling magnetoresistance (TMR). Improving the quality of the MgO barrier to reduce O vacancy concentration would improve TMR in these and similar junctions. [ABSTRACT FROM AUTHOR]

First-principles calculations of the atomic and electronic structure of crystalline CoFeB/MgO/CoFeB magnetic tunnel junctions (MTJs) are performed to understand the effect of B on spin-dependent transport in these junctions. The authors find that it is energetically favorable for B atoms to reside at the crystalline CoFeB/MgO interface rather than remain in the bulk of the crystalline CoFeB electrode. The presence of B at the interfaces is detrimental to tunneling magnetoresistance (TMR) because it significantly suppresses the majority-channel conductance through states of Δ1 symmetry. Preventing B segregation to the interfaces during annealing should result in an enhanced TMR in CoFeB/MgO/CoFeB MTJs. [ABSTRACT FROM AUTHOR]

Interlayer exchange coupling (IEC) in fully epitaxial Fe/MgO/Fe(001) tunnel junctions with wedge-shaped MgO layers is measured at room temperature from the unidirectional shift of the Kerr hysteresis loop. It is found that the IEC is antiferromagnetic for small MgO thickness but changes sign at 0.8 nm. Ab initio calculations of IEC show that this behavior can be explained by the presence of O vacancies in the MgO barrier which makes IEC antiferromagnetic for thin barriers. With increasing MgO thickness the resonance contribution to IEC from localized defect states is reduced resulting in the ferromagnetic coupling typical for perfect MgO barriers. [ABSTRACT FROM AUTHOR]

The exchange interaction parameters of Gd monopnictides are deduced from fitting the total energies of different magnetic configurations to those computed within the Heisenberg model. The magnetic structures predicted by first-principles calculations as well as the Curie (Néel) temperatures obtained from Monte Carlo simulations are both in good agreement with experiments. A detailed analysis of the exchange parameters suggests that the Ruderman-Kittel-Kasuya-Yosida-type indirect exchange interactions and antiferromagnetic superexchange interactions coexist in these compounds. The magnetic order changes from ferromagnetic in GdN to antiferromagnetic in other Gd pnictides as a result of the increased ionic radius of a pnictide in the latter. [ABSTRACT FROM AUTHOR]

A method for the switching of the spin polarization of the electric current injected into a semiconductor is proposed, based on injecting spins from a diluted magnetic semiconductor through a ferroelectric tunnel barrier. We show that the reversal of the electric polarization of the ferroelectric results in a sizable change in the spin polarization of the injected current, thereby providing a two-state electrical control of this spintronic device. We also predict a possibility of switching of tunneling magnetoresistance in magnetic tunnel junctions with a ferroelectric barrier and coexistence of tunneling magnetoresistance and giant electroresistance effects in these multiferroic tunnel junctions. [ABSTRACT FROM AUTHOR]

The microchemistry and magnetism of conventional and high-temperature Sm-Co permanent magnets are investigated by first-principles calculations. Particular emphasis is on the site preference for the substitution of Cu, Ti, and Zr in SmCo5 and Sm2Co17 compounds. Cu substitution is more favorable in the 1:5 phase, in agreement with experimental findings. Titanium and zirconium have positive solution energies for both the phases, with Ti(Zr) having slight preference for the 1:5 (2:17) phase. Some Zr may segregate to the phase boundaries because of its large solution energy. For Ti and Zr the dumbbell site of the 2:17 phase is preferred over the other three inequivalent cobalt sites. These results are used to discuss the observed cellular nanostructure of the high-temperature Sm-Co hard magnets with composition close to the 2:17 phase. [ABSTRACT FROM AUTHOR]

The electrical resistance of a constrained domain wall in a nanojunction is investigated using micromagnetic modeling and ballistic conductance calculations. The nanojunction represents two ferromagnetic electrodes connected by a ferromagnetic wire of 10 nm in length and of a few nanometers in cross section. We find that the anisotropy of the electrodes favors a localization of the domain wall within the constriction (wire) revealing a positive domain-wall resistance. An applied magnetic field moves the domain wall toward one of the electrodes and reduces its width. This compression of the domain wall leads to a sizeable enhancement of the domain-wall resistance. [ABSTRACT FROM AUTHOR]