Small Magnetic Clusters Research Articles

Nontrivial Topological Features and Griffith’s-Phase Behavior in CrFeVGa Probed by Experiment and Theory

We report a combined theoretical and experimental study of the topological semimetal CrFeVGa with an emphasis on the role of atomic disorder on the magnetoelectronic properties. CrFeVGa belongs to the quaternary Heusler alloy family and crystallizes in the cubic structure with B2 disorder. It is found that the disorder plays a crucial role in quenching the magnetization (net moment $\ensuremath{\sim}5\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}2}\phantom{\rule{0.2em}{0ex}}{\ensuremath{\mu}}_{B}$ per formula unit) and other anomalies. Ac and dc magnetization data reveal the occurrence of Griffith's-phase-like behavior in the presence of small magnetic clusters with a weak antiferromagnetic or ferrimagnetic ordering. A nonsaturating, linear positive magnetoresistance is observed even at 70 kOe, in a wide temperature range, which is attributed to the quantum linear magnetoresistance arising due to the zero- or small-gap band structure. Hall measurements show some anomalous behavior (including an anomalous Hall conductivity ${\ensuremath{\sigma}}_{xy0}=270\phantom{\rule{0.2em}{0ex}}\mathrm{S}\phantom{\rule{0.2em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}1}$ and an anomalous Hall angle of 0.07 at 2 K) with a significant contribution from the semimetallic bands. Hall data analysis also reveals the presence of some non-negligible topological Hall contribution, which is significant at low temperatures. Ab initio calculations confirm the topological Weyl behavior of CrFeVGa, which originates from a unique combination of broken time-reversal symmetry and noncentrosymmetry. The nontrivial band topology stems from the $p$ and $d$ states of vanadium, which overlap near the Fermi level. The presence of multi-Weyl points (24 pairs) near the Fermi level causes a large Berry curvature and hence reasonably high anomalous Hall conductivity. The coexistence of so many emerging features in a single material is rather rare and thus opens up new avenues for future topological and spintronics-based research.

Exact classical spin dynamics of high spin nanoscale molecular magnetic clusters

A common feature of many organic-based molecular magnets is that inter-molecular magnetic interactions are extremely weak compared to intra-molecular ones. As a result a bulk sample can be described in terms of independent individual molecular magnets made up of a cluster of a small finite number of coupled magnetic spins. Because of the large value of individual spins of several molecular magnetic compounds it turns out that such systems can be described to very high accuracy, at sufficiently high temperatures, by a classical Heisenberg spin model. Only for sufficiently low temperatures need one incorporate the quantum character of the spins. In this work we focus on the exact classical spin dynamics of small nanoscale molecular magnetic clusters of classical Heisenberg spins. The present study permits us to obtain analytical solutions for the time-dependent spin-spin autocorrelation function for certain clusters of classical Heisenberg spins coupled through exchange interaction. This study underscores the potential utility of a classical spin treatment of nanoscale magnetic clusters and provides results useful to interpret data obtained from experiments.

Crystal field model simulations of magnetic response of pairs, triplets and quartets of Mn3+ ions in GaN

A ferromagnetic coupling between localized Mn spins was predicted in a series of ab initio and tight binding calculations and experimentally verified for the dilute magnetic semiconductor Ga1−x Mn x N. In the limit of small Mn concentrations, x ≲ 0.01, the paramagnetic properties of this material were successfully described using a single ion crystal field model approach. In order to obtain the description of magnetization in (Ga,Mn)N in the presence of interacting magnetic centers, we extend the previous model of a single substitutional Mn3+ ion in GaN by considering pairs, triplets and quartets of Mn3+ ions coupled by a ferromagnetic superexchange interaction. Using this approach we investigate how the magnetic properties, particularly the magnitude of the uniaxial anisotropy field, change as the number of magnetic Mn3+ ions in a given cluster increases from 1 to 4. Our simulations are then exploited in explaining experimental magnetic properties of Ga1−x Mn x N with x ≅ 0.03, where the presence of small magnetic clusters gains in significance. As a result the approximate lower and upper limits for the values of exchange couplings between Mn3+ ions in GaN, being in nearest neighbors (nns) J nn and next nns J nnn positions, respectively, are established.

Computer Simulation of Small Magnetic Clusters of 3d-Transition Metals of the Iron Subgroup Using the Hybrid Density Functional Method

This paper presents the results of s study focused on the stability of small 3d-transition-metal magnetic clusters (metals of an iron subgroup) in spin-polarized states using the hybrid density functional method. Computer modeling and full variational optimization of geometric structures of clusters were performed for various values of the spin multiplicity of electronic states. The binding energies, the bond lengths, and the frequencies of atomic zero-point vibrations in small clusters with a nuclearity of n = 2, 3, 4, 5, 6 were calculated depending on the metal (Fe, Co, Ni) and spin multiplicity M in the zero-charge state. The calculations were carried out using the hybrid density functional B3LYP method in the def2-TZVP basis set of the ORCA package algorithms. A comparison of the calculated results with the available experimental data is presented. It is shown that the calculated data obtained by the hybrid density functional method are in satisfactory agreement with the experimental data for “naked” clusters in inert media both for the spin multiplicity of the ground state and for the energy of atomic shock dissociation of clusters in inert gas flows.

Mössbauer and Magnetic Study of Lanthanum Manganite La1 – xCaxMn0.98Fe0.02O3 + δ (x = 0.05, 0.10, 0.20): Nonstoichiometric and Stoichiometric Composition

Mossbauer and magnetic study of calcium-doped lanthanum manganites La1 – xCaxMn0.98Fe0.02O3 + δ (x = 0.05, 0.10, 0.20) of nonstoichiometric (LCM–NS) and stoichiometric (LCM–S) compositions have been carried out in a wide temperature range. Phase structural separation is observed in the samples of stoichiometric composition (δ = 0). With a decrease in temperature all investigated lanthanum manganite samples exhibit superparamagnetic behavior, caused by the formation of small magnetic clusters in the structure. An expansion of the concentration range toward lower dopant concentrations in the LCM–S samples allowed us to establish the competing processes occurring at a low Ca content, including the Jahn‒Teller effects (orbital order) and the presence of Mn4+ ions (violation of orbital order), and study the dynamics of the structure and magnetic properties as functions of the Ca content.

General method for atomistic spin-lattice dynamics with first-principles accuracy

We present a computationally efficient general first-principles based method for spin-lattice simulations for solids. Our method is based on a combination of atomistic spin dynamics and molecular dynamics, expressed through a spin-lattice Hamiltonian where the bilinear magnetic term is expanded to second order in displacement, and all parameters are computed using density functional theory. The effect of first-order spin-lattice coupling on the magnon and phonon dispersion in bcc Fe is reported as an example, and is seen to be in good agreement with previous simulations performed with an empirical potential approach. In addition, we also illustrate the abilities of our method on a more conceptual level, by exploring dissipation-free spin and lattice motion in small magnetic clusters (a dimer, trimer and quadmer). Our method opens the door for quantitative description and understanding of the microscopic origin of many fundamental phenomena of contemporary interest, such as ultrafast demagnetization, magnetocalorics, and spincaloritronics.

Confinedly tailoring Fe3O4 clusters-NG to tune electromagnetic parameters and microwave absorption with broadened bandwidth

High efficiency and great tunability are becoming hot spot in microwave absorption, drawing great interests of global health researchers. However, meeting the two factors is still a tough challenge. In this work, we demonstrate an easily-tailored absorber of Fe3O4 clusters-nitrogen doped graphene by a facile strategy of confined growth. Small magnetic clusters are uniformly implanted on nitrogen doped graphene, which realizes synergy of dielectric and magnetic loss with good conductivity and improved impedance matching. More significantly, tailoring small Fe3O4 clusters successfully tunes microwave absorption and bandwidth. The minimum reflection loss is greatly increased by ∼7 times, achieving −53.6dB, and the effective bandwidth reaches ∼5GHz with only 1.8mm thickness. Moreover, tailoring the small clusters also drives the absorption peaks from 4.6 to 14.7GHz, covering ∼60% of the investigated frequency. This highly efficient and even frequency-selective microwave absorption endows Fe3O4 clusters-nitrogen doped graphene with wider applications in electromagnetic shielding, microwave absorption, healthcare, information safety and military fields.

Electronic structure, stability and magnetic properties of small M1–4(M = Fe, Co, Ni) clusters encapsulated inside a (BN)48 cage

The geometrical structure and magnetic properties of M1–4(M=Fe, Co and Ni) clusters within a (BN)48 cage were calculated at the BPW91/LanL2DZ level. The small M1–4 clusters generally prefer an off-centered position near the hexagonal rings in the (BN)48 cages. The (BN)48 cages can increase the stability of these small magnetic clusters while protecting the magnetic nature of M and M2 clusters.

Morphology Controlled 1-D Iron Oxide Nanochains with Tunable Magnetic Properties

Magnetic 1-dimension (1-D) ordered nanostructures has stimulated great interests attributed to their potential applications including magnetic resonance imaging, data storage, magnetic sensor, and drug delivery. Self-assembly of 1-D hierarchical nanostructures with aids of surfactant using bottom-up wet chemistry method can provide controllable magnetic properties. Herein, an unusual polymeric additive- polypropylene grafted maleic anhydride (PP-g-MA, 2500 g/mole) has demonstrated its unique capability, i.e., to synthesize 1-D ferromagnetic hard (292.7 Oe) γ-Fe2O3 nanochains made of 24 nm nanoparticles vs. PP-g-MA with 8000 g/mole for the synthesis of 1-D ferromagnetic soft (70.5 Oe) γ-Fe2O3 nanochains (30 nm) made of flowerlike nanoparticles (NPs). Experimental The synthesis procedures of γ-Fe2O3 nanochains were demonstrated as below. First, solid PP-g-MA (0.25 g, Molecular weight, Mn≈8000 or ≈2500) was added into a three-neck flask with 100 mL xylene and heated to reflux (140 °C) for 30 min. Second, brown Fe(CO)5 (3.50 g) was injected into the hot mixed solution (solution turned from transparent to yellow). Then, the solution was further refluxed for 3 hours at 140 °C constantly to form a black colloid. After cooling, the final colloidal solution was used for morphology characterization, while the powder product from drying the colloidal was used for magnetic property measurement. Results and Discussion By using PP-g-MA (Mn≈ 8000), the formation of 1-D nanochains (diameter: ~30.0 nm) was observed in the TEM image, Fig. 1a. The enlarged TEM image in Fig. 1b demonstrates that the building blocks of these nanochains are consisted of unique flower-shape NPs, Selected area electron diffraction (SAED) ring pattern confirm the soleexistence of γ-Fe2O3 in the nano-chains.17 The self-assembled 1-D nanochains can be realized via replacing PP-g-MA (Mn≈ 8000) with PP-g-MA (Mn≈ 2500). When PP-g-MA (Mn ≈ 2500) was used, the formed colloidal NPs were observed to assemble into 1-D nanochains consisting of quasi-spherical NPs instead of the flower shape NP building blocks, when drop-cast on the carbon coated copper TEM grid, the average diameter was ~24.0 nm, Fig. 1c and d. SAED patterns also indicate the sole existence of γ-Fe2O3.1 Figure 1 EM images of γ-Fe2O3 nanochains with a, b) PP-g-MA (Mn≈8000); and c, d) PP-MA (Mn≈2500). Average chain diameter is: a, b) ~30.0 nm, and c, d) ~ 24.0 nm, respectively. The difference in nanochain morphologies are caused by the different capping strength from varying the Mn of PP-g-MA on the magnetic NPs. The MA group in PP-MA can be tightly chemisorbed onto the magnetic NPs2 similar to the carboxylic acid surfactant. 3Larger Mn PP-MA resulted in low MA density in the reaction system, and a lower capping strength on the surface of magnetic NPs was thus observed. At low concentrations, for example, 0.25 g PP-MA (Mn≈ 8000), the aggregation of small magnetic clusters led to the formation of flower-shape NPs grown from the highly concentrated nuclei upon thermal-decomposition of Fe(CO)5. The further assembly of these flower ‘‘aggregates’’ is driven by the balance between attractive forces (magnetic dipolar attractions) and the steric hindrance from the coordinating PP-MA backbones.Beside the morphological difference, different magnetic properties were also observed. Materials with coercivity (H c ) greater than 200 Oe is defined as ferromagnetic hard; while H c smaller than 200 Oe is defined as ferromagnetic soft. Room temperature magnetic property reveals that the γ-Fe2O3 nanochains (30 nm diameter) have higher saturation magnetization (M s ) than that of γ-Fe2O3 nanochains (24 nm diameter), More importantly, the H c of 30 nm γ-Fe2O3 nanochains is about 70.5 Oe, reflecting a ferromagnetic soft material; while the H c of 24 nm γ-Fe2O3 nanochains is 292.7 Oe, corresponding to a ferromagnetic hard material. It can be concluded that the magnetic property such as coercivity (ferromagnetic soft vs. hard) of thus synthesized 1-D nanochains can be easily controlled by only changing the molecular weight of PP-MA. It is believed that the size and aspect ratio, shape anisotropy and magnetization reversal mechanism are responsible for the observed different magnetic property. Conclusion A facile one-pot bottom up approach has been demonstrated to synthesize well defined 1-D γ-Fe2O3 nanochains with easily controlled building block configurations, self-assembly morphologies towards the further manipulation of magnetic property. PP- MA with proper MA grafting density and reaction concentration is of key importance to achieve these evolved different 1-D γ-Fe2O3nanochains. These 1-D nanochains are promising for a variety of applications such as high-density magnetic storage and sensors.

Langevin spin dynamics based on ab initio calculations: numerical schemes and applications

A method is proposed to study the finite-temperature behaviour of small magnetic clusters based on solving the stochastic Landau–Lifshitz–Gilbert equations, where the effective magnetic field is calculated directly during the solution of the dynamical equations from first principles instead of relying on an effective spin Hamiltonian. Different numerical solvers are discussed in the case of a one-dimensional Heisenberg chain with nearest-neighbour interactions. We performed detailed investigations for a monatomic chain of ten Co atoms on top of a Au(0 0 1) surface. We found a spiral-like ground state of the spins due to Dzyaloshinsky–Moriya interactions, while the finite-temperature magnetic behaviour of the system was well described by a nearest-neighbour Heisenberg model including easy-axis anisotropy.

Critical scaling analysis of the itinerant ferromagnetSr1−xCaxRuO3

The critical behavior of ${\mathrm{Sr}}_{1\ensuremath{-}x}$${\mathrm{Ca}}_{x}$${\mathrm{RuO}}_{3}$ was investigated by a scaling analysis based on the Arrott-Noakes equation of state. The critical exponents \ensuremath{\beta}, \ensuremath{\gamma}, and \ensuremath{\delta} of the magnetic critical behavior were extracted for samples with 0 $\ensuremath{\le}x\ensuremath{\le}0.6$ . The ferromagnetic system exhibits a smooth suppression of the Curie temperature ${T}_{\mathrm{C}}$ to zero at a critical concentration ${x}_{c}$ \ensuremath{\approx} 0.7. The ordered magnetic moment decreases simultaneously as expected for itinerant ferromagnets, however, does not vanish completely at ${x}_{\mathrm{c}}$, indicating small magnetic clusters or inhomogeneities. For $x$ = 0, mean-field like exponents are observed. With increasing $x$, the critical exponents \ensuremath{\beta}, \ensuremath{\gamma}, and \ensuremath{\delta} vary nearly linearly from \ensuremath{\beta} \ensuremath{\approx} 0.5, \ensuremath{\gamma} \ensuremath{\approx} 1, and \ensuremath{\delta} \ensuremath{\approx} 3 for $x$ = 0 to \ensuremath{\beta} \ensuremath{\approx} 1, \ensuremath{\gamma} \ensuremath{\approx} 0.9, and \ensuremath{\delta} \ensuremath{\approx} 1.6 for $x$ \ensuremath{\approx} 0.6. The Widom scaling relation is always met for $x\ensuremath{\le}0.6.$ Despite the systematic evolution of the critical exponents as a function of $x$, the exponents cannot be described by any of the universality classes known for classical standard models. The particular trend of the effective critical exponents may be possibly explained by a strong-disorder line of fixed points; the vicinity to ${x}_{c}$ suggests that this behavior is caused by the vicinity to a quantum phase transition.

Encapsulation of small magnetic clusters in fullerene cages: A density functional theory investigation within van der Waals corrections

The encapsulation of magnetic transition-metal (TM) clusters inside carbon cages (fullerenes, nanotubes) has been of great interest due to the wide range of applications, which spread from medical sensors in magnetic resonance imaging to photonic crystals. Several theoretical studies have been reported; however, our atomistic understanding of the physical properties of encapsulated magnetic TM $3d$ clusters is far from satisfactory. In this work, we will report general trends, derived from density functional theory within the generalized gradient approximation proposed by Perdew, Burke, and Ernzerhof (PBE), for the encapsulation properties of the TM${}_{m}$@C${}_{n}$ (TM $=$ Fe, Co, Ni; $m=2\ensuremath{-}6$, $n=60,70,80,90$) systems. Furthermore, to understand the role of the van der Waals corrections to the physical properties, we employed the empirical Grimme's correction ($\mathrm{PBE}+\mathrm{D}2$). We found that both PBE and $\mathrm{PBE}+\mathrm{D}2$ functionals yield almost the same geometric parameters, magnetic and electronic properties, however, $\mathrm{PBE}+\mathrm{D}2$ strongly enhances the encapsulation energy. We found that the center of mass of the TM${}_{m}$ clusters is displaced towards the inside C${}_{n}$ surfaces, except for large TM${}_{m}$ clusters ($m=5$ and 6). For few cases, e.g., Co${}_{4}$ and Fe${}_{4}$, the encapsulation changes the putative lowest-energy structure compared to the isolated TM${}_{m}$ clusters. We identified few physical parameters that play an important role in the sign and magnitude of the encapsulation energy, namely, cluster size, fullerene equatorial diameter, shape, curvature of the inside C${}_{n}$ surface, number of TM atoms that bind directly to the inside C${}_{n}$ surface, and the van der Waals correction. The total magnetic moment of encapsulated TM${}_{m}$ clusters decreases compared with the isolated TM${}_{m}$ clusters, which is expected due to the hybridization of the $d\ensuremath{-}p$ states, and strongly depends on the size and shape of the fullerene cages.

Surface functionalization for tailoring the aggregation and magnetic behaviour of silica-coated iron oxide nanostructures

We report here a detailed structural and magnetic study of different silica nanocapsules containing uniform and highly crystalline maghemite nanoparticles. The magnetic phase consists of 5 nm triethylene glycol (TREG)- or dimercaptosuccinic acid (DMSA)-coated maghemite particles. TREG-coated nanoparticles were synthesized by thermal decomposition. In a second step, TREG ligands were exchanged by DMSA. After the ligand exchange, the ζ potential of the particles changed from − 10 to − 40 mV, whereas the hydrodynamic size remained constant at around 15 nm. Particles coated by TREG and DMSA were encapsulated in silica following a sol–gel procedure. The encapsulation of TREG-coated nanoparticles led to large magnetic aggregates, which were embedded in coalesced silica structures. However, DMSA-coated nanoparticles led to small magnetic clusters inserted in silica spheres of around 100 nm. The final nanostructures can be described as the result of several competing factors at play. Magnetic measurements indicate that in the TREG-coated nanoparticles the interparticle magnetic interaction scenario has not dramatically changed after the silica encapsulation, whereas in the DMSA-coated nanoparticles, the magnetic interactions were screened due to the function of the silica template. Moreover, the analysis of the AC susceptibility suggests that our systems essentially behave as cluster spin glass systems.

Effect of anisotropy on small magnetic clusters

The effect of dipolar interaction and local uniaxial anisotropy on the magnetic response of small spin clusters where spins are located on the vertices of icosahedron, cuboctahedron, tetrahedron and square geometry have been investigated. We consider the ferromagnetic and antiferromagnetic spin-1/2 and spin-1 Heisenberg model with uniaxial anisotropy and dipolar interaction and apply numerical exact diagonalization technique in order to study the influence of frustration and anisotropy on the ground state properties of the spin-clusters. The ground state magnetization, spin-spin correlation and several thermodynamic quantities such as entropy and specific heat are calculated as a function of temperature and magnetic field.

Extrinsic ferromagnetism in epitaxial Co-doped CeO2 pulsed laser deposited films

We report on the structural and magnetic properties of 5 at. % Co-doped CeO2 films grown on LaAlO3(001) substrates by pulsed laser deposition. A series of epitaxially grown samples made under different oxygen partial pressures ranging from 10−4 to 10−1 mbar showed a ferromagnetic signal at room temperature. This signal is independent on the oxygen partial pressure during deposition. X-ray photoelectron spectroscopy showed an increasing concentration of defects as the oxygen pressure during deposition decreases. Although x-ray diffraction and transmission electron microscopy observations could not prove the existence of spurious phases, the temperature dependent variation in the magnetization suggests the existence of small magnetic Co clusters with a large distribution of blocking temperatures.

Novel properties of boron nitride nanotubes encapsulated with Fe, Co, and Ni nanoclusters

Using state of the art spin polarized density functional theory, we report the stability and structural aspects of small magnetic clusters M(4) (M = Fe, Co, and Ni) inside an inert boron nitride nanotube [BNNT(10,0)]. The geometry optimization was carried out starting with various possible configurations [one-dimensional (1D) linear chain, two-dimensional (2D) planar rhombus, and three-dimensional (3D) tetrahedral], and the results reveal that the ground state geometry of M(4) cluster inside the nanotube favors 3D configuration over others. Moreover, these small clusters are found to retain their magnetic nature with a small reduction in the total magnetic moment even after encapsulation. The radial confinement effect on the atomic structure of M(4) clusters was investigated by optimizing the Co(4) (prototype example) in BNNT(10, 0), BNNT(9, 0), and BNNT(8, 0). It is found that with the increase in radial confinement (smaller diameter), the Co(4) cluster becomes more compact, which further leads to significant changes in the electronic and magnetic properties. The electronic density of states analysis of the M(4) clusters inside BNNT(10,0) showed the appearance of additional electronic states in the band gap of BNNT(10, 0). In order to underscore the possibility of functionalizing these encapsulated tubes, we have performed the adsorption of oxygen molecules on it. The adsorption of oxygen in the molecular form with elongated O-O bonds further justifies its application in the oxidative catalysis.

Head/Media Integration Challenge Toward 1 ${\hbox{Tb/in}}^{2}$ Perpendicular Recording

We investigated medium noise using spinstand testing and calculation from the view point of head/media integration for 1 Tb/in 2, focusing on two kinds of noise sources: transition noise in the track center and track edge noise. A quantitative relationship between transition noise and magnetic cluster size of media was clarified. This relationship indicates that the transition noise can be reduced by reducing the magnetic cluster. In the track edge noise, there are two noise sources: edge line fluctuation and increase in transition length at the edges. The edge line fluctuation noise degrades low density SNR. We show that a high cross-track field gradient of writer and small magnetic cluster of media are effective to reduce the edge line fluctuation. The increase in transition length at the edges degrades high linear density SNR. The transition length at the edges increases as transition curvature increases. Both increase in transition length at the edges and large transition curvature make the magnetic write width narrow and erase band width wide. Large track edge noise was observed when the transition curvature was large. Therefore reducing the transition curvature is an effective way to reduce track edge noise. In the micromagnetic calculation for 1 Tb/in2 , high 2 T-SNR of 13.7 dB (1 T: 2200 kfci) at magnetic write width of 54 nm was obtained from a combination of graded Hk media with small magnetic cluster and wraparound shielded writer with high cross-track field gradient and small transition curvature.

First-principles calculation of monitoring spin states of small magnetic nanostructures with IR spectrum of CO

A fully ab initio controlled ultrafast magnetooptical switching mechanism in small magnetic clusters is achieved through exploiting spin-orbit-coupling enabled Λ processes. The idea is that in the magnetic molecules a fast transition between two almost degenerate states with different spins can be triggered by a laser pulse, which leads to an electron excitation from one of the degenerate states to a highly spin-mixed state and a deexcitation to the state of opposite spin. In this paper a CO molecule is attached to one magnetic center of the clusters, which serves as an experimental marker to map the laser-induced spin manipulation to the IR spectrum of CO. The predicted spin-state-dependent CO frequencies can facilitate experimental monitoring of the processes. We show that spin flip in magnetic atoms can be achieved in structurally optimized magnetic clusters in a subpicosecond regime with linearly polarized light.

Dual Segregant Perpendicular Recording Media With Graded Properties

We have introduced structural and magnetic gradations into the granular layer in capped media to promote incoherent switching and hence reduce the contribution of the cap layer to writeability improvement. X-ray photoelectron spectroscopy and transmission electron microscopy revealed that the granular layer was composed of two different microstructures: a well-isolated structure with Si-oxide and Cr-oxide at the bottom portion and a less isolated structure with Si-oxide at the top portion. We found that the graded media exhibit better adjacent track interference (ATI) performance than the conventional media in similar overwrite, magnetic core width, and bit error rate conditions. The graded media have shallower angular dependence of remanent coercivity while maintaining small magnetic cluster size, which is probably the main reason for the improved ATI performance.

Magnetic needles encapsulated inside (BN)36 cage: Prediction of atomic, electronic, and magnetic structure from first principle calculations

Using the first principle based density functional theory formalism, we report the stability and structural aspects of small magnetic clusters inside chemically inert (BN)36 cage. Although the atomic structures of small clusters showed significant changes due to the restrained imposed by the cage size, their stability improves inside the cage. Moreover, their magnetic structure remains almost unaltered inspite of being encaged. The implication of this work indicates that small magnetic particles can be protected inside the BN cage without losing their magnetic character for further applications.