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A systematic experimental study of reverse overwrite (ReOVW) process in the shingled recording scheme has been conducted in conjunction with characterization of corresponding recording performances from recording heads with different geometries. It was found that not only is there no ReOVW reduction as the track density increases, but also ReOVW is, in fact, slightly increased from 300 ktpi to 600 kpi or beyond by using the same writing conditions. These data suggest that conventional magnetic recording technology might be able to extend all the way beyond an areal density of one Tbit/in2 by using the shingled recording scheme.

The response of a trailing shielded perpendicular magnetic recording (PMR) write head with a three-turn two-layer coils is calculated using a full micromagnetic large scale model including return pole and soft underlayer. We study the effect of PMR yoke length and write current overshoot on the dynamic response of the head at high frequency. In particular, recording performance parameter, nonlinear transition shift (NLTS) is simulated using micromagnetic media model. Shorter yoke length head improves NLTS as compared with longer yoke length. Measured NLTS has qualitative agreement with micromagnetic model results.

The interface magnetocrystalline anisotropy (MCA) of (0 0 1), (1 1 0) and (1 1 1) oriented Co/Cu n superlattices ( n ⩽5) was investigated by means of the full potential linearized augmented-plane-wave (FLAPW) method. The results show a marked dependence of the interface MCA on both the orientation and the thickness of the Cu layer. For (0 0 1) oriented superlattices, the small value of the interface MCA with one Cu layer increases significantly as more Cu layers are added. In contrast, the interface MCA of (1 1 0) and (1 1 1) oriented superlattices are not sensitive to the number of Cu layers. The interface MCA is large and positive in the (0 0 1) orientation for n =3 and 5 and slightly positive in the (1 1 1) orientation for n =2 and 5, corresponding to a perpendicular easy axis while the (1 1 0) oriented superlattices show in-plane easy axis.

The in-plane interface magnetocrystalline anisotropy (MCA) of fcc Co (110), either as a free standing monolayer or as an overlayer on a Cu substrate, is investigated using the local density all-electron full-potential linearized augmented plane-wave method. We find an in-plane MCA which has the same order of magnitude as the perpendicular MCA, and which exhibits a significant twofold anisotropy. The results for free standing monolayers calculated with different lattice constants reveal that (i) the strength of the in-plane MCA is severely changed by the strain \char22{} introducing an 8% strain (relative to the Cu lattice constant) induces a five times larger in-plane MCA \char22{} and (ii) the change of band structure due to the strain plays an important role in determining the in-plane MCA. The strength of the in-plane MCA is found to be largely enhanced by the nonmagnetic Cu substrate while it is reduced by the structural relaxation. Interestingly, for all systems the in-plane easy axis is found to lie along $[1\ifmmode\bar\else\textasciimacron\fi{}10$], which is along the direction of the in-plane nearest neighbor atom.

To achieve an electronic level understanding of intergranular embrittlement and its control in steel, the first principles full potential linearized augmented plane wave method and the atomic force approach are used to investigate the effect of Mn additions and P impurities on the energetics and underlying electronic properties of both the Fe grain boundary (GB) and the corresponding intergranular fracture surface (FS). The calculated binding-energy difference is +0.17 eV/adatom for P in the P/Fe binary system, in agreement with its observed embrittlement potency. The Mn is also found to contribute a direct embrittling effect of +0.20 eV/adatom, associated with stronger Mn-Fe chemical bonding in the FS environment. The computed binding-energy difference for P in the (P+Mn)/Fe ternary system is increased to +0.40 eV/adatom, consistent with experimental evidence that Mn facilitates P embrittlement in the grain boundary. The origin of the Mn enhanced P embrittlement is attributed to the strengthened in-plane P-Mn interaction, which makes the P impurity interact more isotropically with the surrounding Mn and Fe atoms in the GB and FS.

The electronic and magnetic structure of fcc Fe has been investigated for a range of lattice constants from a = 3.30 to 3.75 A by the first-principles all-electron linearized augmented planewave method in the local spin-density functional approximation. Electronic band structure, density of states, charge and spin densities of fcc Fe for all known possible magnetic phases of collinear spin configuration are presented and discussed. Besides the previously reported antiferromagnetic, high-spin and two low-spin ferromagnetic phases, a ferrimagnetic phase is predicated to co-exist in the range a = 3.59 – 3.67 A. The calculated moments of the two magnetic sublattices of fcc Fe with Cu lattice constant (a = 3.61 A) are 1.91 and −1.29μB. The total energy of the ferrimagnetic phase is as low as the antiferromagnetic phase which was believed to be the lowest in energy previously.

The multiphoton absorption coefficients of typical crystalline solids are calculated by the first-principles all-electron self-consistent linearized augmented plane wave method in the local-density approximation and the high-order perturbation theory. The crystals studied include the group IV semiconductor Ge, the III–V compound GaAs, II–VI semiconductor CdTe and ionic crystals NaCl and KBr. Calculated 2-, 3-, 4-photon absorption coefficients are approximately in agreement with available experimental data in their orders of magnitude.

The full-potential linearized augmented-plane-wave method with the atomic force approach has been used to determine the interface structure and magnetocrystalline anisotropy (MCA) of a Co monolayer on Cu(111), with and without Cu overlayers. It is found in good agreement with experiment, that the interface MCA for a fully relaxed structure is in-plane with a value of --0.30 meV for Co monolayer (ML) on Cu(111). When capped with nonmagnetic Cu, the interface MCA changes dramatically: for one ML Cu coverage, it is perpendicular to the film plane with a MCA value of + 0.23 meV; for two ML Cu coverage, it rapidly drops to --0.02 meV. Our results confirm that the hybridization at the Co/Cu interface plays an important role in the interface MCA of Co/Cu systems. By comparing the results of the fully relaxed structures with those of unrelaxed structures, we also found that relaxation is important for accurate determinations of the interface MCA. \textcopyright{} 1996 The American Physical Society.

Magnetic structures and magnetocrystalline anisotropy of the Σ3[110](111) grain boundary (GB) in ferromagnetic Fe are investigated by the first-principles full-potential linearized augmented plane-wave method including intra-atomic noncollinear magnetism. In breaking the spatial translation symmetry in a crystalline solid, the GB is found to give rise to a magnetic noncollinearity, where the magnetic moments at both sides of the GB orient at an angle of about 10° with respect to each other. Importantly, the presence of the GB enhances the magnetocrystalline anisotropy energy by one order of magnitude from its bulk value and may induce a pinning effect on the magnetization rotation or magnetic domain wall motion.

Analytic expression for embedded-atom potentials is extended to varieties of cubic and hexagonal materials. These pair potentials are computationally simple and rather accurate. The basic equations are developed and applied to metals and diamond which exhibit different types of bonding. The expressions are used to calculate the vacancy formation energy for bcc Fe and stacking fault energies for several fcc metals. The results are in good agreement with the experimental findings.

The magnetic structure of fcc Fe has been investigated in a range of lattice constants from a = 3.50 to 3.75 A by the first-principles all-electron linearized augmented plane wave method in the local spin-density functional approximation. Besides the previously reported antiferromagnetic phase, one high-spin and two low-spin ferromagnetic phases, a ferrimagnetic phase is predicted to coexist in the range of a = 3.59 to 3.67 A.

We investigate the domain walls in ferromagnetic Fe and antiferromagnetic NiMn with the first principles full-potential linearized augmented plane-wave method including intra-atomic noncollinear magnetism. In both cases, the self-consistent results demonstrate that the magnetization changes continuously from one orientation to another as seen in a Bloch wall. The formation energy of the domain wall (ΔEDW) significantly decreases when the wall thickness increases, which leads to an exchange stiffness of 1.13×10−11 J/m for Fe and 1.43×10−11 J/m for NiMn. The predictions agree with those determined separately for Fe from a phenomenological calculation.

The first-principles calculations within the local density approximation using the full potential linearized augmented plane wave (FLAPW) method were performed to investigate the structural and magnetic properties of the Ta/NiFe interface for both clean NixFe1−x (001) thin films and with a Ta overlayer. To study the composition dependence, we adopted x=0.5 (L10 structure with either Fe or Ni layers on the surface) and 0.75 (L12 structure with mixed Fe-Ni layers or with Ni on the surface). The equilibrium overlayer/substrate distance and the preferred site position of Ta were obtained by structural optimization employing atomic-force calculations and total energy comparisons for several possible adsorption sites of Ta. By comparing with results for the clean surface of five-layer NixFe1−x (001) films, we found that Ta has a significant detrimental effect on the magnetic properties of NiFe with its induced magnetic moment coupled ferro- or antiferro-magnetically with the substrate depending sensitively on t...

First-principles local density full potential linearized augmented plane wave method and state-tracking and torque approaches are employed for the theoretical determination of in-plane and off-plane magnetic anisotropy for both free standing planar Co stripes and the same film put on a Cu (100) substrate, with and without nonmagnetic Cu decoration. The easy magnetic axis is found to lie parallel to the stripes for clean Co stripes; the decoration with nonmagnetic Cu is found to switch the easy axis from parallel to perpendicular to the stripes. The magnetic anisotropy coefficients are determined and the magnetic behavior is related to, and explained in terms of, their electronic structures and the fundamental bonding properties of the constituent atoms.

The electronic and magnetic structure of Fe/Cu(001) superlattices are investigated with the first-principles all-electron linearized augmented plane wave method in the local spin-density functional approximation. The results show that the magnetic moment of the interface Fe layer is stabilized at the high spin state of the fcc Fe crystals. When the thickness of Fe layers is larger than two monolayers, the interior layers always exhibit an antiparallel spin configuration in its lowest energy phases.

The structural, electronic, and magnetic properties of monolayer Mn on an Fe(111) substrate are determined using the local spin density total energy full potential linearized augmented plane wave method and atomic force approach. A strong interplay between magnetism and atomic structure is found, e.g., the interfacial Fe layer undergoes a large downward relaxation by 0.59 a.u. from the ideal bcc position. As was found previously for bulk fcc Mn and Mn/Fe(001), the equilibrium Mn–Fe bond length is larger in the ferromagnetic state (4.47 a.u.) than that in the antiferromagnetic (AFM) state (4.31 a.u.). The AFM coupling between Mn and Fe is the ground state. The interplay between the interfacial magnetic coupling in the Mn/Fe(111) and the multilayer relaxation is discussed.

We generalize the full-potential linearized augmented plane-wave method with a single slab geometry in order to treat noncollinear magnetism with no shape approximation for the magnetization, and apply this scheme to investigate free-standing Fe(001) monolayers with lattice constants matching those of fcc Ag(001) and Cu(001) substrates. Intra-atomic noncollinear magnetism on a smaller length scale inside the atom is observed in the ferromagnetic state, and is found to enhance the magnetocrystalline anisotropy energy (by 17∼20%) compared to values determined for their collinear magnetic state.

Both collinear and noncollinear magnetic structures of FeMn with ${L1}_{0}$ atomic ordering were determined from total-energy full-potential linearized augmented plane-wave calculations incorporating noncollinear magnetism with no shape approximation for the magnetization density. Different spin-density orientations for the different band states are observed on a smaller length scale inside an atom. The presence of the intra-atomic noncollinear magnetism enhances the stability of the $3Q$ noncollinear magnetic structure, in which the magnetic moments align toward the center of the cell of four atoms, thus becoming the lowest-energy state of the structures considered.

The magnetic structures at the compensated ferromagnetic/antiferromagnetic (FM/AFM) interface of exchange bias FM NiFe/AFM NiMn films were determined with first-principles full-potential linearized augmented plane-wave calculations including noncollinear magnetism. The results predict that the magnetic moments of the FM NiFe layer lie perpendicular to those of the AFM NiMn layer. The intra-atomic noncollinear magnetism that arises near the interface is found to play an important role in stabilizing the perpendicular coupling that leads to a large biquadratic exchange energy (BEE). The BEE is large enough to require formation of a magnetic domain wall (with an estimated thickness $\ensuremath{\sim}370 \AA{})$ in the AFM NiMn layers, which may account for the observed large coercivity and exchange bias. We also discuss magnetic structures at a rough FM/AFM interface---as simulated in model calculations with the inclusion of line step defects---which may contribute to a unidirectional magnetic anisotropy.

First-principles electronic structure studies based on local spin density functional theory and performed on extremely complex simulations of ever increasingly realistic systems, play a very important role in explaining and predicting surface and interface magnetism. This has led to solving even more challenging problems like the embrittlement of the Fe grain boundary, discussed here. Now, a major issue for first-principles theory is the treatment of the weak spin-orbit coupling (SOC) in magnetic transition metals and their alloys and its subsequent effects: (i) A major breakthrough in eliminating the numerical randomness for the determination of the magneto-crystalline anisotropy was made with the state-tracking and torque approaches. This now enables us to treat magnetostriction and its inverse effect, strain-induced magnetic anisotropy in transition metal bulk, thin films and alloys, (ii) The magneto-optical Kerr effects and x-ray magnetic circular dichroism are now directly calculated and compared with experiment. In all this work, and more recently, on the first-principles calculations of giant magneto-resistance in multilayers, extensive first-principles calculations and model analyses provide simple physical insights and guidelines to search for new magnetic recording and sensor materials.

Incomplete magnetization switching may take place between two recorded transitions in perpendicular magnetic recording. These write process issues were studied with a micromagnetic model. The relatively poor effective field from the central part of the perpendicular writer is unable to reverse the media grains properly. Consequently, media dc noise will increase as the incomplete switching becomes more severe. An expression for the effective field heff was proposed to easily discover those cases. The incompletely switched magnetization observed in the static footprint could also be partially transferred into the dynamic write process. The calculated media signal-to-noise ratio on a pseudorandom sequence could be reduced by as much as 3dB (compared to the fully switched case). On the other hand, transition quality does not become worse with a smaller heff. This insensitivity to the transition quality was caused by the magnetostatic field from the opposite magnetization polarity on the other side of the rec...

The full potential linearized augmented plane wave method and atomic force approach are employed for the theoretical determination of interface magnetocrystalline anisotropy (MCA) for superlattice systems of Co/Cu in (001), (110), and (111) orientations, and overlayer systems of the monolayer Co on Cu (111) substrate adsorbed by different further coverage of Cu. It is found in superlattices that the interface MCA is sensitive to the geometry arising from different orientations. In good agreement with experiment, the interface MCA with Cu overlayers is found to peak at 1 monolayer of Cu‐coated Co/Cu(111) and then to decrease with further Cu deposition. In addition to the hybridization of electronic states at the Co/Cu interface, the interaction between the interface layers and the next‐to‐interface layers in superlattices and structure relaxation in overlayers may have a significant influence on the MCA of the Co layer.