The writing quality of magnetic recording improves with increasing sharpness of the written transitions. Ultimately, the transition sharpness is limited by the grains themselves, and no longer depends on the head field gradient. In this study, we varied the head field gradient by changing the head-media spacing and characterized the write quality by transition jitter and equalized signal-to-noise (eSNR) measurements. Consistent with a recording in the grain size limit, we discovered that the write quality did not improve with smaller head to medium spacings. We also found that the measured values for the jitter and the eSNR are close to what is estimated for grain size limited recording.

We present a study of the magnetic reversal mechanism for exchange coupled composite perpendicular media, i.e., hard granular layer/exchange-coupling layer (ECL)/soft layer (SL) systems, without soft underlayer. Using a vibrating sample magnetometer, the out-of-plane and in-plane components of the magnetization are monitored simultaneously, while sweeping an external out-of-plane magnetic field. The in-plane signal reveals the reversible rotation of the magnetization during the switching process. The amplitude of this rotation is correlated with the variations in coercivity and angular dependence of the remanent coercivity for different ECL and SL thicknesses.

We have studied the recording performance of perpendicular exchange spring layer (ESL)-media for hard disk drive recording. In particular, we investigated the role of interlayer coupling by varying the thickness of a nonmagnetic coupling layer (CL). We demonstrate that not only the media writeability is improved upon optimizing the CL thickness, but also that substantial recording performance improvements can be achieved due to improved media noise properties. The potential of these media structures for high areal density recording is demonstrated by performing areal density measurements, which showed a substantial improvement for optimally coupled ESL-media.

A Monte Carlo approach and a modified nudged elastic band method are used to study the dynamic coercivity of interacting particle arrays in particular perpendicular recording media and exchange spring bilayers. Monte Carlo simulations are performed to study the effect of the interactions on the dynamic coercivity of interacting particle arrays. It is shown that the interactions in magnetic recording media only slightly influence the dynamic coercivity. The reliability of energy barrier measurements based upon Sharrock's equation for frequency-dependent coercivity data is investigated using a modified nudged elastic band method. It is shown that the extrapolated energy barrier at zero field may deviate from the correct one by up to 18% if the conventional exponent n=1.5 is assumed. Our micromagnetic simulations furthermore indicate that the accuracy of the extrapolated energy barrier can be improved by about a factor of 3 upon measuring the dynamic coercivity at an angle of 45 degrees and using the exponent n as an additional fit parameter.

This paper investigates the effect of varying the exchange-break-layer thicknesses (leading to a change in intergranular exchange) on spectral rolloff and the transition parameter (a-parameter). The rolloff curves are obtained by measuring the amplitude of the fundamental harmonic peak at each written density. A systematic increase of the low frequency amplitude is observed as the EBL thickness decrease.

The effect of intergranular exchange on the transition parameter (a) in perpendicular oxide composite media was investigated. Two different methods were used to vary the amount of intergranular exchange present in the films. The inter layer (IL) thickness was varied for one series of sample, while for the other, the oxygen (O 2 ) flow was changed during deposition. The transition parameter was extracted using a read-back model to fit experimental rolloff curves for both series. The exchange was quantified by calculating alpha values from the experimental (M-H) loops. It was found that increasing the intergranular exchange in the recording layer lead to a reduction of the transition parameter by up to 12% for alpha values in the range of 2.2. These results were achieved for both methods of varying exchange and lead to very similar range of alpha values

Two media, A and B, are discussed to illustrate the media requirements and properties for the 230Gb∕in2 demonstration. A and B had similar layer structures except that the recording layers had different oxide compositions and that the exchange break layer thicknesses were 21 and 13nm, respectively. They had similar coercivity and intrinsic switching field but showed large difference in writability. Consequently, even though they achieved similar performance for heads down to a track width of 150nm, medium A could not be saturated adequately for heads with a track width of 120nm. On the other hand, medium B possessed the desirable properties for high density recording and formed the base for the media that were used in the 230Gb∕in2 demonstration.

We have evaluated the magnetic properties and recording potential of longitudinal exchange spring recording media. The media structure consists of a low anisotropy CoCrX spring layer ferromagnetically coupled to a high anisotropy CoPtCrB hard layer via a CoRu interlayer. The interlayer exchange coupling is tuned by varying the CoRu layer thickness. The short-time coercive field (Hc0) as well as the energy barrier (KuV) of the structure are furthermore tuned by varying the thickness of the spring layer. We show that by changing the CoCrX layer thickness from 1to4nm, Hc0 can be decreased by a factor of 2 while the energy barrier can be increased by up to 50% hence improving the stability of the overall structure. More importantly, it is possible to reduce the switching field distribution width leading to an improved overall signal to noise ratio in this CoCrX thickness range.