FIG 1 - uploaded by Alfonso Cebollada
Content may be subject to copyright.
a Specular 2 x-ray scan of 1000-Å-thick film of FePt001/ MgO001. The complete structure was 18 Å Pt/Fe 0.52 Pt 0.48 /150 Å Pt/ MgO001. b Specular x-ray scan of 943-Å-thick film of FePt001/ MgO001. The complete structure was 18 Å Pt/Fe 0.50 Pt 0.50 / 7 Å Pt/MgO001.
Source publication
Growth of epitaxial films of the L1 0 phase of FePt, with the tetragonal c axis along either the film normal or in‐plane, is described. Films were grown by coevaporation of Fe and Pt, under ultrahigh vacuum conditions, onto a seed film of Pt grown on MgO or SrTiO 3 substrates. The perpendicular or in‐plane orientation of the c axis was controlled b...
Similar publications
The L1 0 ordered MPt(001) thin films (M = Fe or Co) are very interesting for perpendicular recording due to their magnetic anisotropy and magneto-optical behaviours. Epitaxial L1 0 -ordered NiPt(001) / FePt(001) bi-layers were co-deposited on MgO(100) substrates by MBE. The L1 0 order parameter is high with the concentration modulation along the gr...
Solid-state synthesis of a Sm 2 Co 7 (110) hard magnetic phase prepared by successive deposition of Co and Sm layers onto a MgO(001) surface at a temperature of 400 °С has been experimentally studied. Upon annealing at 500 °С, the structure of the material changes, which leads to the formation of an epitaxial Sm 2 Co 17 (110) phase. The first and s...
The thickness dependence of the fourfold in-plane magnetic anisotropy was first observed in epitaxial Fe(001) films and described by the volume anisotropy of bcc Fe with a positive anisotropy constant (K<sub>1</sub><sup> vol </sup>≫0) superimposed by a negative interface term (K<sub>1</sub><sup> int </sup>≪0). This results in a spin reorientation o...
The in-plane magnetic anisotropy in the Fe/MgO/GaAs(001) system has been carefully studied as a function of MgO thickness. The epitaxial relation is Fe(001)[110]//MgO(001)[100]//GaAs(001) [100] for d(MgO)>1 monolayer (ML). The interfacial uniaxial anisotropy was greatly reduced by the MgO interlayer, and the easy axis of the fourfold anisotropy was...
Single-crystalline RFe2(110) compounds (R=Y, Sm, Gd, Tb, Dy0.7Tb0.3, Dy, Er, and Lu) have been grown by molecular-beam epitaxy. Compared to the bulk compounds, the thin films exhibit modifications of the magnetic anisotropy, related to the strains induced during deposition. We present here a detailed determination of in-plane and out-of-plane param...
Citations
... This can be larger than the magnetic field generated by a write head, which is approximately 2 T [4]. ≥60 B , was estimated experimentally from the anisotropy constant of the thin film or non-equiatomic [7][8][9][10]. However, the magnetic anisotropy constant depends strongly on the temperature, size, and shape of the nanomaterial. ...
𝐿10 FePt nanoparticle is among the most promising materials for magnetic recording and nanomagnetic applications. In nanoparticles, the superparamagnetic effect, wherein the thermal fluctuation is comparable to the energy barrier for magnetic flips, strongly affects the stability of magnetic recording. The temperature dependence of the magnetic anisotropy constant in 𝐿10 FePt nanoparticles is a crucial factor for estimating the relaxation time of magnetic flips in a magnetic nanoparticle. However, comprehensive simulations of the atomic level for energy barrier for magnetic flips in the 𝐿10 FePt nanoparticles are lacking. This study entailed a simulation that quantitatively reproduced the size dependence of the Curie temperature of nanoparticles in the experimental studies. Moreover, the surface effect, wherein the magnetization decreases owing to the loss of magnetic exchange interaction pairs on the surface, was also clarified. The temperature and size dependences of energy barrier for the magnetic flips of 𝐿10 FePt nanoparticles were elucidated.
... This rather low value (a fully ordered system would have S = 1) shows that the chemical order of the tetragonal L1 0 phase is incomplete. Previous reports found that FePt deposited on a Pt or Au seed layer on MgO(110) also grow in the L1 0 structure with its c axis oriented in plane [10,[21][22][23][24][25], however, the c axis was reported to be canted out of the film plane when deposited directly on MgO(110) [26,27]. ...
Magnetic exchange springs (ESs) are composed of exchange-coupled hard and soft magnetic layers, i.e., layers with high and low anisotropy, respectively. The moments in the soft layer can be wound up by applying an external field, which has to be smaller than the anisotropy field of the hard layer. Alternatively, an ES can be realized by biasing the soft magnetic layer by two adjacent hard magnetic layers with different magnetic anisotropy directions. We have fabricated an ES layer stack by magnetron sputter deposition. As the hard magnetic bottom layer, we used epitaxial FePt L10, and as the top layer Co with both layers having different in-plane easy axes. These hard layers pin the moments of a soft permalloy (Ni81Fe19) layer sandwiched between them, winding up an ES at remanence. The anisotropy of the polycrystalline top Co layer was engineered by glancing-angle deposition to have in-plane easy axis anisotropy perpendicular to the easy direction of the bottom layer. Using soft x-ray spectroscopy and magneto-optical measurements, we found the in-plane ES to extend from the soft layer into the top layer of our FePt/permalloy/Co trilayer structure.
... The critical size of FePt nanoparticle to have the thermal stability against the superparamagnetic effect, with ≥60 B , is estimated in the experiment from the anisotropy constant of the thin film or non-equiatomic [7,8,9,10]. However, the magnetic anisotropy constant should be intensely dependent on the temperature, size, and shape of the nano-material. ...
... The MAE of L1 0 FePt bulk obtained in DFT with spin-orbit coupling is 14.4 MJ/m 3 (2.52 meV/f.u), which is slightly higher than the value in the experimental works of L1 0 FePt thin film and non-equiatomic [8,9,10] being 4-11 MJ/m 3 . The last term denotes the interaction of the spin at site with the external magnetic field. ...
... Chemical order refers to the atomic preferred occupation or displacement at spatial sites, providing dominated near-coordination environment around the specified atoms and new features of chemical bonds 1,2 . Accompanied with the rearrangement of the lattice potential field and spatial channels in crystals 3,4 , chemical order has been viewed as one of the promising approaches to tailor functionalities or explore new properties 5,6 . ...
Chemical ordering is a common phenomenon and highly correlated with the property in solid materials. By means of the redistribution of atoms and chemical bonds, it invokes the effective lattice adjustment and tailors corresponding physical properties. To date, however, a direct probe to the 3D interfacial interactions of chemical ordering remains a big challenge. In this work, we deciphered the interlaced distribution of the nanosized domains with chemical order/disorder in Fe3Pt bulk alloy. HAADF-STEM images evidence the existence of such nanodomains. The reverse monte carlo method with the X-ray pair distribution function data reveal the 3D distribution of local structures and the tensile effect in the disordered domains at the single-atomic level. The chemical bonding around the domain boundary changes the bonding feature in the disordered side and reduced the local magnetic moment of Fe atoms. This results in a suppressed negative thermal expansion and its extended temperature range in Fe3Pt bulk alloy with nanodomains. Our study demonstrates an elaborate local revelation for the chemical order/disorder nanodomains in bulk alloy. The understanding gained from the atomic short-range interactions within the domain boundaries provides useful insights to design new functional compounds.
... Because of the potential for improving thermoelectric performance by exploiting the magnetic degree of freedom [16][17][18][19], thermoelectric transport in magnetic materials, including transition metal and alloys, gained renewed attention recently [20][21][22][23]. L10 FePt holds a special place among these materials, with a large magnetocrystalline anisotropy K u > 10 7 J/m 3 highly desirable for overcoming the superparamagnetic effect in magnetic data storage and spintronic devices [24][25][26][27][28]. ...
We report unconventional thermoelectric power (Seebeck coefficient, S) in L10 structured FePt films. The temperature dependence of S can be well fitted by a phenomenological expression consisting of electron diffusion and magnon-drag contributions. Interestingly, the magnon drag coefficient carries an opposite sign to that of electron diffusion, revealing a dominant contribution from the elusive electron-magnon Umklapp scattering. Density-functional theory calculations identify several bands crossing the Brillouin zone boundaries, facilitating the Umklapp process. The large spin–orbit coupling in FePt results in strong mixing of majority and minority spins among some of those bands, greatly enhancing the electron-magnon scattering.
... However, choosing materials with high magnetocrystalline anisotropy (MAE) is preferable in order to avoid the effects of the super-paramagnetic limit. Among these materials, L1 0 -FePt which present strong magnetocrystalline anisotropy K u (≃ 7-10 10 7 erg/cm 3 ) [2][3][4] occupies a promising place in potential technological applications such as heat-assisted magnetic recording applications (HAMR) [5,6], and as ultra high-density recording media [7]. The high magnetocrystalline anisotropy (MAE) of L1 0 -FePt arises from the strong spin-orbit interaction (SOI) of Pt, and hybridization between Fe 3d and Pt 5d states [8][9][10][11]. ...
... Using these optimized lattice parameters, we calculate bulk magnetocrystalline anisotropy (K B v ) of 2.56 meV/ f.u, i.e. 1.28 meV/atom, close to 2.59 meV/ f.u found recently [36]. A review of MAE calculations is presented in [20], where values spread from 1.3 to 4 meV/f.u. and the experimental results are close to 1.2 meV/ f.u (≃ 7 x 10 7 erg/cm 3 ) [2][3][4]37,38]. The discrepancy in calculated values are due to different calculation methods and simulation parameters used by the authors. ...
We carried out first-principle calculations of magnetocrystalline anisotropy of L10-FePt thin films terminated by either perfect Fe (Pt) layers or defect surfaces, including vacancies or substituted surface atoms. Inspired by the experimental strategy for determining magnetic anisotropy, we present here a theoretical model for analyzing volume and surface magnetic anisotropies for L10-FePt thin films with different surface terminations. We demonstrate that surface anisotropy does not depend solely on the film thickness, but also on the atomic environment of the surface layer. Perpendicular surface anisotropy of L10-FePt thin films reaches its maximum with full Pt termination, which decreases with increasing Pt vacancies and becomes parallel to the surface for a full Fe surface. In the case of mixed surfaces, surface anisotropy of (3Pt,1Fe) is enhanced compared to platinum-rich surface with one vacancy, and tends to be more in-plane for an iron-rich surface (3Fe,1Pt). Our results could be used to study surface anisotropy effects on L10-FePt surfaces by mean of classical magnetic models, and they are very promising for the development of high density magnetic data storage such as magnetic memory.
... L1 0 -type FePt alloy is a key material for magnetic recording media because of its strong magnetocrystalline anisotropy. [1][2][3][4] Heat-assisted magnetic recording is a promising technology for achieving further increases in recording density in hard-disk drives. 5,6) However, the high Curie temperature T C of FePt of approximately 750 K causes energy dissipation and also can lead to serious damage by heating in writing operations. ...
We studied the Curie temperature TC variation in L10-type FePt ordered alloys that were partially substituted with other transition metal elements, such as Mn, Cu, Ru, and Rh, by first-principles calculations. For the theoretical evaluation of TC, a disordered local moment approach based on the coherent potential approximation was employed. The calculated results reveal that the most significant reduction in TC was observed for FePt where some Pt was substituted by Ru, while a large uniaxial magnetic anisotropy constant on the order of 10⁷ erg/cm³ was maintained. An analysis of the electronic structure demonstrates that the stability of the ferromagnetic state is degraded by the substitution of Ru.
... Chemically ordered L1 0 FePt alloy thin films exhibiting large perpendicular magnetic anisotropy (PMA) of up to 7 MJ/m 3 [1][2][3] are being implemented in data storage media for heat-assisted magnetic recording, which is expected to extend the current areal density of 1 Tb/in. 2 toward 3-4 Tb/in. 2 [4][5][6][7][8]. The material properties of FePt can be tailored by adding third elements, e.g. ...
We have studied structural and magnetic properties of (FePt)1−xTbx thin films grown at elevated temperatures on MgO(100) substrates. The incorporation of Tb into the chemically ordered L10 FePt lattice gives rise to considerable changes in the structural and magnetic properties, depending on the Tb content and the deposition temperature. When grown at 770∘C, pronounced L10 ordering of the initial FePt phase is present. It vanishes gradually with Tb addition, thereby forming additional crystalline Tb-Pt phases at higher Tb content. These structural changes are accompanied by a strong reduction of the perpendicular magnetic anisotropy with increasing Tb content, finally resulting in a soft magnetic material with in-plane easy-axis magnetization. Extended x-ray absorption fine-structure measurements were performed to examine the possible incorporation of Tb into the FePt lattice. Based on the number of Pt first neighbors, the transformation from the initial tetragonal L10 structure to the chemically disordered fcc (A1) phase with increasing Tb content could be firmly concluded. In a further sample series, FePt was grown at a lower temperature of 530 °C, which leads to reduced initial L10 chemical ordering. Adding Tb results in strong elastic stress in the lattice, eventually causing full amorphization of the film. Interestingly, in this case, a spin-reorientation transition from in-plane to out-of-plane magnetic easy axis is found at low temperatures, which is associated with an anisotropic chemical short-range order present in the amorphous phase. Furthermore, x-ray magnetic circular dichroism studies at the FeL3,2 and Tb M5,4 edges for all samples reveal strong antiferromagnetic coupling between Fe and Tb, resulting in a reduction of the net magnetization of the film.
... Chemically ordered L1 0 FePt alloy thin films, comprising of equal amounts of Fe and Pt, can exhibit large perpendicular magnetic anisotropy (PMA) of up to 70 Merg/cm 3 . [1][2][3] Recently, these films have been implemented as storage material for applications in heat-assisted magnetic recording (HAMR), which is expected to further extend the areal density towards 3-4 Tb/inch 2 . [4][5][6][7][8] While high PMA is needed for thermal stability of today's hard disk drives, it poses a challenge to magnetic writing heads, as heat assistance is generally required in order to reverse the magnetization direction. ...
In this study, we have investigated the effect of Gd implantation on composition, chemical order, and magnetic properties of 20 nm thick L10 ordered FePt thin films. We show that upon Gd implantation at 30 keV even a small amount of 1 at. % is sufficient to destroy the L10 order, resulting in a soft magnetic A1 FePt alloy, with the exception of a thin L10 ordered layer located at the film/substrate interface. Additionally, a strong resputter effect is observed which results in a large decrease in film thickness as well as to a reduction in Fe content in the FePt alloy. Post-annealing of samples in Ar atmosphere did not result in a restoration of the L10 order, but leads to a transformation to pure Pt and Fe2O3, facilitated by the presence of a high density of vacancies induced by the implantation process.
... In most cases, these changes in the structure involve diffusion based processes, thus by exploiting processes like grain boundary diffusion, or GB diffusion induced reaction layer formation, GBDIREAC, low temperature processing could be reached. In order to get the magnetically favourable L1 0 phase, post annealing of the disordered A1-FePt phase [151], growing at high temperature on suitable substrates [152], can be used. Additionally the grain size and crystal orientation (texture) should likewise be controlled for applications. ...
Interdiffusion along grain boundaries can lead to shift of grain boundaries in form of Grain Boundary Diffusion Induced Grain Boundary Migration, DIGM, in systems forming wide range solid solutions, and to the Grain Boundary Diffusion Induced Solid State Reactions, in systems containing intermetallic phases. If, during above processes, the grain size of the sample is smaller than the double of the migration distance complete homogenization can also be reached (cold homogenization). Atomic mechanisms and phenomenological description of such alloying are reviewed. The main driving force, at low temperatures where the bulk diffusion is completely frozen out, arises from the unequality of the grain boundary atomic fluxes, leading to stress accumulations. The cold homogenization is the manifestation of such stress relaxations. Reviewing experimental data, we illustrate that DIGM takes place on both sides of a binary AB thin film and the solute content in the DIGM zone is higher on the side of the component of higher melting point (i.e. in the slower component). In binary systems containing intermetallic compounds the cold homogenization can lead, either to the formation of a given stoichiometric compound, or to two phase equilibrium, in accordance with the phase diagram. Different possible applications are likewise surveyed.
