Minimum Switching Field Research Articles

Radio Frequency Field Dependence of Microwave‐Assisted Switching Behaviors of Co/Pt Nanodots

SUMMARYMicrowave‐assisted magnetization switching (MAS) has been expected as one of the prominent future ultra‐high‐density magnetic recording technologies. In this paper, we have studied the radio frequency (RF) field dependence of the switching behavior of Co/Pt nanodot arrays with various dot diameters. While the critical frequency increases and the minimum switching field decreases with increasing the RF field, MAS behavior critically depends on the dot size. For small dots less than 130 nm in diameter, the critical frequency and the minimum switching field exhibit linear variation with the RF field. On the other hand, for the larger dots (dot diameter ≥ 230 nm), they exhibit not only profound MAS effect but also obvious change in the behavior at a certain RF field. These changes of MAS behaviors are explained as a consequence of the change of magnetization precession mode. On the other hand, the dispersions of MAS effect exhibit no remarkable variation on the RF field.

Co/Ptナノドットにおけるマイクロ波アシスト磁化反転の交流磁場強度依存性

Microwave-assisted magnetization switching MAS has been expected as one of the prominent future ultra-high-density magnetic recording technologies. In this paper, we have studied the radio frequency RF field dependence of the switching behavior of Co/Pt nanodot arrays with various dot diameters. While the critical frequency increases and the minimum switching field decreases with increasing the RF field, MAS behavior critically depends on the dot size. For small dots less than 130i¾źnm in diameter, the critical frequency and the minimum switching field exhibit linear variation with the RF field. On the other hand, for the larger dots dot diameter i¾ź 230i¾źnm, they exhibit not only profound MAS effect but also obvious change in the behavior at a certain RF field. These changes of MAS behaviors are explained as a consequence of the change of magnetization precession mode. On the other hand, the dispersions of MAS effect exhibit no remarkable variation on the RF field.

High-Areal Density Recording Simulation of Three-Layered ECC Bit-Patterned Media With a Shielded Planar Head

Magnetic parameters of the previously proposed three-layer exchange coupled composite (ECC) dot were modified to compensate the additional perpendicular anisotropy from the shape and the stacking of the layers. The modification in the magnetic parameters resulted in a minimum switching field and applied field angle dependence of the field. Recording simulation using a multistepped shielded planar head field on the bit-patterned media with modified three-layer ECC dots suggested possibility of a high-areal density recording above 4 T dot/in\(^{2}\) with no energy assist scheme. It was also concluded that magnetic parameter compensation for additional shape and stacking anisotropy is indispensable for ECC dots.

Theoretical Research on Microwave Assisted Magnetic Moment Reversal in Magnetic Recording Media

The minimum switching field threshold and switching speed are key parameters for the magnetic recording in writing. This paper presents the dynamic precession of the moments of the grains based on LL equation.Under microwave-assisted reversal conditions, the influence of the differences between the angle of Anisotropy field on the magnetic moment reversal and loading speed of reversal magnetic field in two interacting particles is investigated.

Inter/intra granular exchange and thermal activation in nanoscale granular magnetic materials

We explain the effect of inter/intra granular exchange coupling and thermal activation on the switching behavior of nano-scale granular magnetic materials. For an ideal, non-interacting granular system, the minimum switching field occurs at 45° from the easy axis of the grains. We show through simulation and measurements, using a CoCrPt oxide-segregated granular film as a model system, that there is a clear shift in the angle of applied field at which the minimum switching field occurs. This arises solely due to incoherent reversal induced by inter-granular exchange coupling or incoherency within larger grains, rather than thermal activation.

Theoretical Study on the Microwave Assisted Reversal of Magnetic Moment for Graining

This paper presents the dynamic precession of the moments of the grains based on LL equation, and the impact of the interaction between the grains on the minimum switching field threshold and the speed of the switching process in the microwave field is investigated.As an isolate grain, microwave assisted switching could enhance minimum switching field threshold and switching speed.

Simulating Study on Microwave Assisted Switching of Ferromagnetic Moment for Grains

The minimum switching field threshold and switching speed are important parameters for the magnetic recording in writing. This paper presents the dynamic precession of the moments of the grains based on LL equation, and that the impact of the volume of the grain on the switching speed is investigated under the condition of microwave assisted switching of magnetic moment.

An excellent crystal for high resistance against optical damage in visible-UV range: near-stoichiometric zirconium-doped lithium niobate

Near-stoichiometric zirconium-doped lithium niobate crystals were fabricated and their optical damage resistance was investigated. It was found that these crystals can withstand a light intensity of 20 MW/cm2 at 514.5 nm cw laser, 80 GW/cm2 at 532 nm pulse laser, and 120 kW/cm2 at 351 nm cw laser. The minimum switching field is only 1.00 kV/mm for 0.5 mol% zirconium-doped lithium niobate crystal. These properties suggest that the near-stoichiometric zirconium-doped lithium niobate crystals will be an excellent candidate for quasi-phase matching technique.

Analysis of Microwave Assisted Magnetization Switching in Magnetic Material

The minimum switching field threshold and switching speed are key parameters for the magnetic recording in writing. This paper presents the dynamic precession of the moments of the grains based on LL equation.Under microwave-assisted reversal conditions, the influence of loading speed of reversal magnetic field in two interacting particles is investigated.

Exchange-coupled perpendicular media

The potential of exchange spring bilayers and graded media is reviewed. An analytical model for the optimization of graded media gives an optimal value of the magnetic polarization of J s=0.8 T. The optimum design allows for thermally stable grains with grain diameters in the order of 3.3 nm, which supports ultra-high density up to 5–10 Tbit/in 2. The switching field distribution is significantly reduced in bilayer media and graded media compared to single-phase media. For the graded media the switching field distribution is reduced by about a factor of two. For bilayer media the minimum switching field distribution is obtained for soft-layer anisotropies that are about one fifth of the hard-layer anisotropy. The influence of precessional switching on the reversal time and the reversal field is investigated in detail for magnetic bilayers. Exchange spring bilayers can be reversed with field pulses of 20 ps.

Angular dependence of switching field measured on maghemite recording particles

The switching field, H 0, required to reverse the magnetic moment of an elongated single-domain particle, depends on the angle θ between applied field and magnetization axis of the particle, in a way related to the reversal mode. A macroscopic method based on measurements of induced remanent magnetizations was used to reveal the angular dependence of the switching field for acicular γ-Fe 2O 3 recording particles. Separate data were obtained for four particle fractions of differing coercive force. For the particles investigated reversal is most readily achieved when the field is applied at low angles to the easy axis, as is expected when the magnetic moments are reversing by incoherent rotation of the atomic spins. Furthermore, it appears that the relative increase of H 0( θ) for high θ is smaller for particles of higher minimum switching field.