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In this article, we present the fabrication of FePt/FePt-BN/FePt-SiOx and conventional FePt/FePt-C for heat-assisted magnetic recording (HAMR) on Corning Lotus NXT glass substrates. For FePt/FePt-BN/FePt-SiOx media, a 2.5 nm FePt/FePt-35vol.%BN was fabricated on polycrystalline MgO underlayers at 700 °C to serve as the templated layer for the growth of 4 nm FePt-35vol.%SiOx at 550 °C. For the FePt/FePt-C media, 6.5 nm FePt/FePt-C media was fabricated at 550 °C with FePt and C co-sputtered on top of 0.5 nm FePt. Both media show well-isolated FePt grains, which are fully surrounded by the grain boundaries materials. Compared with FePt/FePt-C media, the FePt/FePt-BN/FePt-SiOx media show distinctively smaller grain-to-grain pitch distance or higher grain areal density. Moreover, the bimodal grain-size distribution that is often observed in FePt/FePt-C media has been suppressed in the FePt/FePt-BN/FePt-SiOx media. In addition, both media show good magnetic properties on Corning Lotus NXT glass substrate. [ABSTRACT FROM AUTHOR]

The Curie temperature distribution induced from grain size variation in heat-assisted magnetic recording (HAMR) can be alleviated by including the thermally insulating magnetic grain boundaries. In this paper, we present a systematic micromagnetic study on this new type of HAMR media, focusing on the impact to the recording behaviors from the exchange coupled magnetic boundary (shell). It is found that the soft magnetic shell of higher Curie temperature is capable of assisting the switching of FePt grain in both magnetization and transition process. The important implication of the proposed media for practical HAMR recording is that optimal performance now can be accomplished with relaxed recording conditions in both head field intensity and the heating source, eventually enhancing area density capability and the overall HAMR system stability. [ABSTRACT FROM AUTHOR]

Grain size and size distribution reduction in L10 FePt granular thin film is becoming critical to increase the areal storage density and realize the full potential of heat-assisted magnetic recording media. FePt and amorphous carbon or mixture with other segregants are often deposited at elevated temperature in order to promote the L10 ordering in FePt. Due to the materials system and high temperature involved in the fabrication process, the bimodal distribution of the grains is often observed with a significant amount of small grains with diameter <3 nm. The bimodal distribution of the grains could potentially lead to a significant microstructure nonuniformity and thus grain-to-grain properties variation, such as Curie temperature (Tc), texture, ordering, and magnetic properties. In this paper, we performed a detailed analysis on microstructure evolution of FePt-C thin film during the growth process on different initial layer conditions to understand the origin of bimodal grain size distribution in the FePt-C media. Experimental modeling study of depositing FePt on continuous carbon layer at elevated temperature was conducted to understand the nucleation and growth process. [ABSTRACT FROM AUTHOR]

In this paper, we present systematic micromagnetic modeling investigation on recording process of segmented thin-film media with circularly polarized magnetic field at microwave frequencies. This paper provides insightful understanding about the segmented medium stack design in microwave-assisted magnetic recording (MAMR) by exploring the impact of signal-to-noise (SNR) ratio and recording track width. By utilizing segmentation of grains with exchange breaking layers, the ac magnetic field generated from spin torque oscillator can be best exploited. Via optimized medium stack design, MAMR is able to achieve both high SNR and areal density gain with the proposed notched-structure medium (top and bottom segments have the strongest crystalline anisotropy) compared with conventional graded medium (with gradually increasing anisotropy from top to bottom). By tuning crystalline anisotropy strength in top and bottom segment, we studied the MAMR behavior of SNR and track width under different ac frequencies. This provides a novel view for future segmented media design. [ABSTRACT FROM AUTHOR]

Transition curvature in heat-assisted magnetic recording can be eliminated by appropriately varying head field amplitude across recording track width. In this paper, we present a systematic micromagnetic study on the effects of non-vanishing field beyond track edges in practical head designs, focusing on the recording characteristics beyond track edges. It is found that a uniform field amplitude beyond track edges will create wing-like patterns beyond straightened transitions, forming erase bands at high linear densities. The width of the erase band decreases if the head field diminishes beyond track edges. However, for practical field reduction gradients beyond track edges, the width of the erase band still remains significant. [ABSTRACT FROM AUTHOR]

Temperature dependence of medium anisotropy field is an important property for recording performance in heat-assisted magnetic recording. In this paper, we report a pump–probe technique to characterize the temperature dependence of the anisotropy field. An experimental measurement is performed on two prototype FePt L10 -based recording media samples, which shows different temperature dependences of anisotropy field. Micromagnetic modeling study validates and provides further understanding of this technique. The simulation result shows the excellent agreement of an obtained value with actual medium property, especially near Curie temperature. [ABSTRACT FROM PUBLISHER]

By averaging multiple writes of opposite polarity waveforms captured synchronously from heat-assisted magnetic recording (HAMR) media, we distinguish random noise of the HAMR writing process from the spatially anti-correlated repeatable noise due to media microstructure variations. We show both analytically and experimentally how the normalized cross correlation coefficient, $R$ , of two opposite polarity waveforms quantifies the random and repeatable dc-noise fractions, showing where dc-noise reduction efforts should be concentrated. The value of $R$ also reflects the degree of media saturation. At optimal recording conditions for the head and media studied here, the total dc-noise comprises appreciable fractions of both random and repeatable noise. The experimental results are supplemented with micromagnetic modeling and analytic calculations. [ABSTRACT FROM PUBLISHER]

In this paper, we present a spin-stand testing study of heat-assisted magnetic recording (HAMR). Motivated by the understanding of the major recording noise mechanisms predicted by previous modeling, experiments were made to investigate the recording field/write current dependence of signal-to-noise ratio. The two significant noise mechanisms in HAMR, incomplete switching and erase-after-write, have been observed in the experiments and shown to be similar to the previous modeling results. Previous simulations indicate that system performance strongly correlates with recording time window (RTW). Therefore, head/media relative velocity was varied to change the RTW, and the effects of linear velocity are also compared. Further analysis has been applied to cases with different writer and media components. These results help understand the field/media requirements to optimize the HAMR recording system performance. [ABSTRACT FROM AUTHOR]

In this paper, we present a micromagnetic analysis on two key noise mechanisms for current FePt-L10-based heat-assisted magnetic recording (HAMR) media: grain-to-grain variations of anisotropy field and Curie temperature. We found that the signal-to-noise ratio (SNR) versus heating power measurement could be used to distinguish the noise arising from these two different origins. We also found that in today's HAMR media, the dominate noise origin is likely to be the combination of Curie temperature distribution and heating, or temperature, variation from grain to grain. As one of the possible mechanisms for grain-to-grain heating variation, the effect of grain boundary thickness distribution is studied in terms of its impact to recording SNR. It is concluded that reducing the combined heating and Curie temperature distribution is critical for the realization of the area density capability gain promised by the technology. [ABSTRACT FROM AUTHOR]

In this paper, we present a micromagnetic modeling study on the switching property of segmented grains assisted by circularly polarized magnetic field at microwave frequencies and the actual recording process. This paper provides insightful understanding of the switching dependence on the Gilbert damping constant and the optimization for suppressing the impact of possible damping constant distribution. The recording processes with ac field generated by a spin torque oscillator on the media consisting of segmented grains are also investigated. In this microwave assisted magnetic recording (MAMR) process, the segmentation of the grains with exchange breaking layers enables the best utilization of the ac field. The MAMR simulations show significant signal-to-noise ratio (SNR) gain over today's perpendicular recording for medium for media with grain pitches <8~nm. Grain-pitch limited SNR performance can be achieved for medium grain pitches as small as 5 nm while achieving sufficient thermal stability simultaneously. At 4.5 nm grain pitch, MAMR shows significantly higher SNR than that predicted by corresponding HAMR simulations. It is concluded that MAMR should enable areal density capability of 4 Tb/in^2 and beyond and its SNR performance is superior to HAMR at all densities. [ABSTRACT FROM PUBLISHER]

Generally distributions in anisotropy field and grain-to-grain exchange are considered to be the main sources of noise in heat assisted magnetic recording (HAMR). Through systematic micromagnetic modeling based upon the Landau–Lifshitz–Bloch (LLB) equation , however, we show that variation in the Curie temperature from grain-to-grain is the primary contributor to noise in HAMR. Additionally, small and narrowly-distributed exchange coupling turns out to be helpful under certain circumstances or changes the noise format. These could be explained by the recently proposed HAMR noise mechanism and related recording patterns. [ABSTRACT FROM PUBLISHER]

The impact of RuAl underlayers and TiN intermediate layers on the microstructure, L10 ordering, and coercivity of granular FePt thin films is evaluated with an emphasis on controlling the FePt grains by using a new underlayer system. The use of the single RuAl/TiN film stacks does not help induce the epitaxial grain pick-up for FePt media due to their overly small grain size and smooth surface morphology. Two-step-deposited RuAl layers are developed to make a more open microstructure. By sputtering the top RuAl layers at low power and high Ar pressure, it is shown that there is a one-to-one grain matching between RuAl/TiN and FePt. It is also found that TiN underlayers are more favorable to the L10 ordering process compared to MgO underlayers. [ABSTRACT FROM AUTHOR]

In this paper, we report a micromagnetic modeling study on the recording processes in heat-assisted magnetic recording. By solving coupled Landau-Lifshitz-Bloch equations, recording simulations are performed for granular \FePt-L10 thin film media. The calculated signal-to-noise ratio shows strong dependence on recording field amplitude, especially for media of small size grains. It is found that low field amplitude yields unsaturated recording whereas high field amplitude causes transitions to be broadened immediately after writing. High thermal gradient will alleviate the transition broadening, allowing high field amplitude to be employed so that completed magnetization in the recorded bits can be achieved in small grin size media. The study concludes that the ability in obtaining the expected signal-to-noise ratio performance at very small grain pitches would critically rely on whether sufficiently high thermal gradient can be achieved in the media. [ABSTRACT FROM AUTHOR]

In this paper, we present a systematic micromagnetic modeling investigation on the segmented perpendicular thin film media. Segmented medium with inserted exchange breaking layers not only enables tunability of the crystalline anisotropy at each segment through the medium thickness, but also enables a continuous tuning of the inter-segment ferromagnetic exchange coupling strength. It is found that the switching field distribution can be significantly narrowed by optimizing the inter-segment coupling. This is because for a three-segment grain, the switching field dependence on the anisotropy field variation of the segment with highest anisotropy field can be substantially suppressed with adequate inter-segment coupling. Recording simulation shows that optimizing the inter-segment coupling strength combined with the optimization of anisotropy field for each segment, significant SNR enhancement can be achieved. Although optimizing the inter-segment coupling does yield reduction of the energy barrier, it also reduces the switching field in proportion, such that the anisotropy strength can be engineered with sufficient thermal stability. It is argued that as long as the grain size is smaller than half of the bit length, segmenting the medium grains presents an alternative and likely more effective approach than that of reducing the grain size for increasing the area density capability. [ABSTRACT FROM AUTHOR]

Bit patterned media (BPM) is a promising technology for hard disk drive recording at ultra-high areal densities of 1 Tbit/in^2 and beyond. However, for BPM to be commercially viable, nanoscale bit patterns must be fabricated at low cost on a large scale and with low defect densities. The most likely route to realizing such criteria is through the use of high throughput nanoimprint lithography followed by direct etching of the recording media, where the bit pattern template is generated by highly accurate electron beam mastering tools. In this work, we experimentally demonstrate the merits of rotary stage electron beam mastering and the subsequent effects of direct pattern transfer on BPM and servo arrays patterned into 2.5'' commercially available CoCrPt perpendicular recording media (PRM) at a density of 366 Gbit/in^2. The 42 nm pitch staggered bit patterns and corresponding servo arrays were lithographically generated by a Pioneer Corporation EBR-401 rotary stage electron beam mastering system and subsequently transferred into the media using a series of reactive ion etching and ion milling processes with C/SiNx mask structures and a novel Al protection layer. The fabricated media was recorded and read back with a commercial recording head to verify pattern fidelity. [ABSTRACT FROM AUTHOR]

In this paper, we present a set of systematic experimental investigations on possible noise mechanisms for current perpendicular thin film media of small grain sizes. In particular, we focus on intergranular exchange coupling and grain boundary surface anisotropy in the granular layer of the present continuous-granular-composite film structure. Micromagnetic modeling studies are conducted to study the impact of the observed experimental phenomenon. Modeled experiments show that significant intergranular exchange coupling may occur when oxide grain boundary thickness becomes less than 1 nm. If the grain boundary thickness has significant distribution below this critical value, the exponential dependence of the coupling strength on the oxide thickness would yield significant degradation of the medium signal-to-noise ratio. Carefully designed experiments have also been conducted to study possible grain boundary interfacial anisotropy. Co/Cr, CoPt/Cr, Co/SiO2, Co/Cr2 O3, and Co/TiO2 interfaces are investigated and the corresponding interfacial anisotropy strengths are quantitatively measured. Although Co/SiO2 interfacial anisotropy appears to be the weakest among them, the measured interfacial anisotropy energy strengths for all of them are significant fractions of the crystalline perpendicular anisotropy of the grains at present grain sizes. Finally, we investigated the impact of stacking faults in hcp Co-alloy grains. It is found that when the anisotropy strength of a small segment of a grain substantially reduces due to the existence of stacking faults, it will yield a switching field reduction disproportional to the volume ratio of the segment. [ABSTRACT FROM AUTHOR]

Heat-assisted magnetic recording utilizes material with drastically changing crystalline anisotropy during the heating and cooling process. In this paper, the impact of media anisotropy near Curie temperature on medium signal-to-noise ratio (SNR) is systematically studied. Results show that the combination of proper gradient of anisotropy versus temperature and thermal profile is crucial to achieving satisfactory SNR and recording areal density. [ABSTRACT FROM AUTHOR]