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We report a systematic study of the switching and recording characteristics of perpendicular magnetic recording media in which the exchange coupling between granular oxide and continuous cap layers was varied. The interfacial exc...
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We report a systematic study of the switching and recording characteristics of perpendicular magnetic recording media in which the exchange coupling between granular oxide and continuous cap layers was varied. The interfacial exchange coupling strength was controlled by adjusting the magnetization $({rm M}_{rm s})$ and the thickness (t) of the exchange control layer (ECL) between granular oxide and cap layers. The media switching mechanism highly depends on the oxide-to-cap exchange coupling strength as well as the relative moment ratio of cap and oxide layers. Reversal process is coherent for medium with only granular oxide layer and becomes incoherent with incorporation of ECL and continuous cap layers. Optimizing granular oxide-to-cap exchange coupling improves the media writeability as well as the media signal-to-noise ratio $({rm SNR}_{rm m})$. At optimum exchange coupling condition, the switching field is significantly reduced even with higher thermal stability factor (${rm K}_{rm u} {rm V/k}_{rm B}$ T). However, when the interlayer coupling strength is too weak, independent switching of oxide and cap layers occurs, resulting in poor writeability and high media noise. An optimum design of oxide-to-cap exchange coupling is critical in attaining recording properties for high density recording through selection of appropriate ECL and cap materials.
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Epitaxial La_(0.67)Ca_(0.33)MnO_3/CaMnO_3 (LCMO/CMO) bilayers and the reference single layers were deposited by pulsed laser deposition on (001)- and (110)-oriented SrTiO_3 (STO) substrates, allowing us to perform a detailed study...
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Epitaxial La_(0.67)Ca_(0.33)MnO_3/CaMnO_3 (LCMO/CMO) bilayers and the reference single layers were deposited by pulsed laser deposition on (001)- and (110)-oriented SrTiO_3 (STO) substrates, allowing us to perform a detailed study of the dependence of exchange coupling on crystal orientations. It is found that the exchange bias (coercive) field of the (110)-oriented LCMO/CMO bilayer are decreased (increased) compared to that of (001)-oriented bilayer, due to the enhanced (weakened) Mn~(3+)-Mn~(4+) ferromagnetic double-exchange interaction of LCMO layer. It is clear that the spin flop coupling that leads to the enhanced coercivity and the spin glass state that results in the exchange bias effect can coexist and are determined by the competition between Mn~(3+)-Mn~(4+) ferromagnetic double-exchange and Mn~(4+)-Mn~(4+) antiferromagnetic super-exchange interactions at the interface. We propose that strong Mn~(3+)-Mn~(4+) ferromagnetic double-exchange interaction facilitates the existence of spin flop coupling, not the formation of spin glass state at the LCMO/CMO interface.
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Exchange-coupled magnetic nanocomposite powders were obtained by mechanically milling ferromagnetic (FM)-antiferromagnetic (AFM) powders. A shift in the field-cooled (FC) hysteresis loop and the coercivity enhancement of the FM ph...
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Exchange-coupled magnetic nanocomposite powders were obtained by mechanically milling ferromagnetic (FM)-antiferromagnetic (AFM) powders. A shift in the field-cooled (FC) hysteresis loop and the coercivity enhancement of the FM phase ensuing from exchange bias anisotropy was observed. The blocking temperature$(T_B)$in all composites was found to be much lower than the Neel temperature$(T_N)$of the AFM phases. A model based on Preisach hysteresis was used to calculate the interfacial energy between FM and AFM particles. The calculated interfacial energies were highest for FM-CoO and lowest for FM-CuO composites. These values are in good agreement with those reported for polycrystalline AFM thin films.
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L1_0-FePt based perpendicular exchange coupled composite (ECC) films with both weak FePt interparticle exchange coupling (IPEC) and strong hard/soft exchange coupling (HSEC) are virtually crucial to improve the signal-to-noise rat...
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L1_0-FePt based perpendicular exchange coupled composite (ECC) films with both weak FePt interparticle exchange coupling (IPEC) and strong hard/soft exchange coupling (HSEC) are virtually crucial to improve the signal-to-noise ratio and the writability of recording media concurrently. This article reports synthesis and magnetic property tunability of the L1_0-FePt:Au/Fe ECC film with low IPEC between neighboring L1_0-FePt particles and strong HSEC between the hard L1_0-FePt:Au composite layer and the soft Fe layer. Moreover, the magnetic domain configuration study reveals the domain wall assisted magnetization reversal mechanism. The coupled Fe layer facilitates reverse nucleation and magnetization reversal in the L1_0-FePt:Au composite layer, leading to remarkable reduce of the switching field while maintaining high thermal stability.
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The origin of the magnetic anisotropy energy barriers in a series of bpym~2 (bpym = 2,20-bipyrimidine) radical-bridged dilanthanide complexes [(Cp~*_2Ln)_2(μ-bpym)]~+ [Cp~* = pentamethylcyclopentadienyl; Ln = Gd~(III) (1), Tb~(II...
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The origin of the magnetic anisotropy energy barriers in a series of bpym~2 (bpym = 2,20-bipyrimidine) radical-bridged dilanthanide complexes [(Cp~*_2Ln)_2(μ-bpym)]~+ [Cp~* = pentamethylcyclopentadienyl; Ln = Gd~(III) (1), Tb~(III) (2), Dy~(III) (3), Ho~(III) (4), Er~(III) (5)] has been explored using density functional theory (DFT) and ab initio methods. DFT calculations show that the exchange coupling between the two lanthanide ions for each complex is very weak, but the antiferromagnetic Ln-bpym~+ couplings are strong. Ab initio calculations show that the effective energy barrier of 2 or 3 mainly comes from the contribution of a single Tb~(III) or Dy~(III) fragment, which is only about one third of a single Ln energy barrier. For 4 or 5, however, both of the two Ho~(III) or Er~(III) fragments contribute to the total energy barrier. Thus, it is insufficient to only increase the magnetic anisotropy energy barrier of a single Ln ion, while enhancing the Ln-bpym~-couplings is also very important.
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We investigate a tight-binding model on a two-dimensional square lattice with three terms: the Rashba spin-orbit coupling, the real amplitude next-nearest spin-orbit coupling, and an exchange field. We calculate the first Chern nu...
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We investigate a tight-binding model on a two-dimensional square lattice with three terms: the Rashba spin-orbit coupling, the real amplitude next-nearest spin-orbit coupling, and an exchange field. We calculate the first Chern number to identify band topology. It is found that the Chern number takes the quantized values of C_1 = 1,2 and the chiral edge modes can be obtained. Therefore our model realizes the quantum anomalous Hall (QAH) effect. The Rashba coupling is positive for the QAH phase while the next-nearest coupling is detrimental to it. By increasing the exchange field intensity, the Chern number changes from quantized value 2 to 0. The behavior of the edge states is also studied. Particularly for C_1 = 2 case, there are two gapless spin-polarized edge states with the same spin polarization moving in the same spatial direction. This indicates that their appearance is topological rather than accidental.
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The temperature dependences of interfacial exchange coupling in Co/semiconductor (SM)/Fe trilayers (SM≡Si or Ge) with different spacer thicknesses are investigated. Only one step is found in the third (not in the first) quadrant ...
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The temperature dependences of interfacial exchange coupling in Co/semiconductor (SM)/Fe trilayers (SM≡Si or Ge) with different spacer thicknesses are investigated. Only one step is found in the third (not in the first) quadrant of the hysteresis loop of the trilayers with different SM thicknesses, which is ascribed to a larger interfacial coupling strength of Co/CoGe (or Co/CoSi) than of Fe/FeGe (or Fe/FeSi). Furthermore, in comparison with Co/Ge/Fe, a smaller exchange bias field H_E and no clear step are observed in Co/Si/Fe, which may originate from the weaker interfacial coupling in this trilayer. The variation of coercivity H_C with spacer thickness at low temperatures in Co/Ge/Fe is different from that in Co/Si/Fe, indicating again the important effect of the SM layer in the trilayers.
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MCSCF calculations are performed in order to determine the exchange coupling between the 2p electrons of the N atom and the LUMOs of the fullerene cage in the case of mono- and tri-anions of N@C-60. The exchange couplings provided...
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MCSCF calculations are performed in order to determine the exchange coupling between the 2p electrons of the N atom and the LUMOs of the fullerene cage in the case of mono- and tri-anions of N@C-60. The exchange couplings provided our calculations are in the range of 1.5 meV which is large compared to the hyperfine interaction. The strong coupling can explain the missing EPR signal of the nitrogen in paramagnetic anions.
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By controlling the phase distribution and interfacial conditions, the composites of (soft)Ni_(0.6)Zn_(0.4)Fe_2O_4/ (hard) SrFe_(12)O_(19) ferrites were prepared with different mass ratios f_s of soft magnet. The coercivity mechani...
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By controlling the phase distribution and interfacial conditions, the composites of (soft)Ni_(0.6)Zn_(0.4)Fe_2O_4/ (hard) SrFe_(12)O_(19) ferrites were prepared with different mass ratios f_s of soft magnet. The coercivity mechanism was analyzed according to the theory for melt-spun and sintered magnets. Using the modified Brown's equation, we derive the exchange coupling coefficient α_(ex) that can be quantification-ally expressed as α_(ex)=α_0 exp( -f_s/f_0) with α_0 and f_0 being constants, which has not been reported before as far as we know.
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Control of magnetic states by external factors has garnered a mainstream status in spintronic research for designing low power consumption and fast-response information storage and processing devices. Previously, magnetic-cation s...
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Control of magnetic states by external factors has garnered a mainstream status in spintronic research for designing low power consumption and fast-response information storage and processing devices. Previously, magnetic-cation substitution was the conventional approach to induce ferromagnetism in an intrinsic antiferromagnet. Theoretically, anion doping is proposed to be another means to change magnetic ground states. Here, the authors demonstrate the synthesis of high-quality single-phase chromium oxynitride thin films using in-situ nitrogen doping. Unlike antiferromagnetic monoanionic chromium oxide and nitride phases, chromium oxynitride exhibits a robust ferromagnetic and insulating state, as demonstrated by the combination of multiple magnetization probes and theoretical calculations. With increasing the nitrogen content, the crystal structure of chromium oxynitride transits from trigonal (R3 over bar c) to tetragonal (4 mm) phase and its saturation magnetization reduces significantly. Furthermore, they achieve a large and controllable exchange bias field in the chromia heterostructures by synthetic anion engineering. This work reflects the anion engineering in functional oxides towards potential applications in giant magnetoresistance and tunnelling junctions of modern magnetic sensors and read heads.
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