Angular Dependence Of Switching Field Research Articles

Study of Erase Band and Write Performance for Shingled Magnetic Recording With FePt-Based Exchanged Coupled Composite Media

The shingled magnetic recording (SMR) with $\text{L}1_{0}$ -FePt-based exchange coupled composite (ECC) media is a promising way to achieve ultrahigh recording density. During the writing process, the insensitive angular dependence of switching field provided by ECC media is found to play an important role in mitigating transition noise and adjacent track erasure, furthermore the investigation indicates that the skew angle (SA) and corner angle (CA) of wide main pole inevitably affect the erase band noise in SMR. Hence, this paper studies an improved calculation method of erase bandwidth (EBW) to evaluate the erase band noise more accurately, and investigates the impact of SA and CA on write performance. Additionally, by investigating the bit error rate of adjacent track’s bits caused by the erasure, the results show that the high angular tolerance of switching field provided by $L1_{0}$ -FePt(6 nm)/[Co/Ni]5(4 nm) ECC media can effectively reduce EBW. Finally, the analyses demonstrate that an optimum combination of writer CA, tapered angle, and suitable range of SA is helpful to reduce erase band noise and improve the write performance.

Relationship Between Applied Field Gradient and Magnetization Switching in ECC Structured Dots

The dependence of the switching of magnetic dots with a composite structure on applied field gradients is investigated. The dot size and magnetic properties were targeted at 2 Tbit/in -class bit patterned media. In the case of a head field with only a perpendicular component, the switching probability can be considered to be the fraction of the dot volume in which the field exceeds the average switching field of the dot when measured in a globally uniform field. The switching probability also depends on the recording field gradient within the dot. On the other hand, in the case of a vector recording field with in-plane components, the switching probability can be approximated by considering the angular dependence of switching field, calculated in a globally uniform field. Additionally, down-track write margins are estimated and found to increase logarithmically as the gradient is increased.

Exchange Coupled Composite Media

Exchange coupled composite (ECC) media consisting of both magnetically hard and soft regions within the same grain have been proposed for 1 Tb/in2 perpendicular magnetic recording. Compared to conventional perpendicular media, a composite structure can effectively decrease the switching field of the media without a loss in thermal stability. This paper reviews the recent work on composite media including two spin and complete micromagnetic models for ECC media, exchange spring media, synthetic antiferromagnet ECC media, and experimental results in support of these theories. The figure of merit (defined as xi = 2E/(MsHsV), where DeltaE, Ms, Hs, and V are energy barrier, saturation magnetization, switching field, and grain volume of the media, respectively) of composite media is found to be 2 ~ 3 times that of conventional media. Therefore, grain volume can be decreased and the impact of the magnetic recording ldquotrilemmardquo reduced. The switching mechanism of composite media is discussed and its properties such as angular dependence of switching field and thermal attempt frequency is studied and compared with conventional media. Results for micromagnetic simulation of recording on ECC media are shown together with a brief discussion of write head design for ECC media.

Effect of shape anisotropy on the magnetization reversal process of (Ga,Mn)As ferromagnetic semiconductors

We have carried out the planar Hall effect measurement on two different sizes of Hall bar devices fabricated from GaMnAs ferromagnetic films. The detailed information on the magnetic anisotropy properties including the shape anisotropy field were obtained from the angular dependence of planar Hall resistance. The shape anisotropy field per magnetization in the device with 10μm channel width was about 39G. Though the value of shape anisotropy is small, it affects the magnetization reversal processes of the 10μm Hall device by showing steplike feature in the angular dependence of switching fields.

Fast switching in single-domain particles with uniaxial quartic anisotropy

The effect of quartic anisotropy on angular dependence of the high-speed switching behavior for uniaxial particles is studied. For large applied field angles with respect to the anisotropy axis, the magnetization reversal is dominated by the precessional switching and the switching speed is very fast in the presence of quartic anisotropy. The quartic anisotropy enhances the switching fields moderately, and expands the precessional switching regime towards the anisotropy axis, while slightly increases the switching time for the applied field magnitude larger than the anisotropy field. The angular dependence of switching field exhibits a broad minimum around the field angle of 45° for large quartic anisotropy. The results have implications for improving the recording characteristics of the tilted media.

Angular dependence of the switching field and implications for gyromagnetic remanent magnetization in three-axis alternating-field demagnetization

The critical field for reversing the magnetic moment of a single-domain (SD) grain, the switching field, is a function of the angle between the field and the grain's easy axis of magnetization. The functional relationship derived for coherent reversal, i.e. spins reversing in unison, differs from that of various incoherent mechanisms and of domain wall movement in multidomain (MD) grains. Due to the angular dependence of the switching field, uniaxial alternating-field (AF) demagnetization is less efficient than AF demagnetization with tumbling of the sample. The difference was determined for synthetic and natural rock samples carrying anhysteretic and rotational remanent magnetizations (ARM and RRM respectively). These types of remanence were chosen to activate dominantly SD grains, and their magnitudes relative to saturation isothermal remanent magnetization (SIRM) are discussed in relation to magnetic grain size. For the samples studied, data indicated that the majority of remanence carriers cannot be associated with the Stoner—Wohlfarth model for coherent reversal. In contrast, incoherent reversal or domain wall movement largely explains the observed lag. Based on the angular dependence of switching field corresponding to these models, the acquisition of gyromagnetic remanent magnetization (GRM) during three-axis demagnetization is discussed. In particular it is shown theoretically that the method of Dankers and Zijderveld fails to eliminate completely the effect of GRM in three-axis demagnetization.

Magnetization reversal of iron nanoparticles studied by submicron Hall magnetometry

Magnetization of an array of 16 elongated iron nanoparticles with diameter of ∼7 nm and height of ∼100 nm has been studied with a submicron semiconductor Hall magnetometer. Details of the magnetization hysteresis curves and the angular dependence of switching fields are examined. The results indicate that the magnetization reversal in these cylindrical nanoparticles cannot be described with a single coherent rotation mode.

Angular dependence of the switching field of thin-film longitudinal and perpendicular magnetic recording media

An experimental survey of the angular dependence of the remanent switching fields for longitudinal and perpendicular magnetic recording media is presented and compared to the Stoner–Wohlfarth and Kondorsky models of magnetic switching. An experimental procedure is used where the remanence measured in the easy-axis direction is used to define the switching field for all angles of the applied field. Clear differences between different types of media are found. CoPtCrB alloy longitudinal recording media are found primarily to have a Stoner–Wohlfarth switching character. In contrast, the switching of perpendicular Co/Pd multilayer media is a mixture of Stoner–Wohlfarth rotation and domain-wall motion.

Magnetization reversal of individual nanowires with controlled defects

Low temperature magnetization reversal measurements were performed on individual permalloy nanowires of diameters between 30 and 60 nm. During the electrochemical growth of the wire, a defect was induced by a short pulse in the deposition potential modifying locally the microstructure and composition. Magnetic measurements performed with micro-superconducting quantum interference devices were performed. The angular dependence of switching field revealed significant deviations from classical predictions. For specific angles, magnetization curves indicate a reversal occurring in two steps.

Angular dependence of switching field of magnetic recording particles

In a magnetic recording media, anisotropic particles are placed with different directions in the head field. The switching field, H s of a particle at a certain direction is defined as the minimum field, which reverses its easy axis magnetization. To determine the position of magnetization transition in recording media, one needs the angular dependence of the switching field. To find this for a texture of anisotropic single domain particles, the acicular iron particles with 0.3 μm length have been grown in a magnetic field. Then, the textures of the particles have been oriented by another magnetic field. We have measured the remanent magnetization of samples m r( θ) and m r( H), respectively, as functions of angle and field by a VSM system. The easy axis distribution is obtained from m r( θ), then the distribution and m r( H) is used for determining the angular dependence of the switching field. Results show that H s for small angles is <20% of the anisotropy field of the particles H k. This difference from the Stoner–Wohlfarth model is explained by using particles interaction.

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.

Magnetisation reversal by uniform rotation (Stoner–Wohlfarth model) in FCC cobalt nanoparticles

The combination of high sensitive superconducting quantum interference device (SQUID) with high quality nanoparticles allowed to check the simplest classical model describing the magnetisation reversal by uniform rotation which were proposed more than 50 yr ago by Néel, Stoner and Wohlfarth. The micrometer sized SQUIDs were elaborated by electron beam lithography and the nanoparticles were synthesised by arc-discharge. The measured angular dependence of switching fields of nearly all FCC. Co nanoparticles revealed a dominating uniaxial magnetic anisotropy. This result suggests that twin boundaries and stacking faults strongly alter the cubic magnetocrystalline anisotropy leading to dominating uniaxial anisotropy. However, few particles were sufficiently “perfect” in order to show a more complex switching field surface and a field path dependence of the switching field which is the important signature of the cubic magnetocrystalline anisotropy.

Switching field distribution of magnetic fine particles

In the magnetic recording media the switching field distribution (SFD) is an important micromagnetic characteristic curve. However, in general case, methods of assessing SFD have not presented a reasonable relation between the macroscopic measurements and the microscopic properties of the system. The degree of alignment of particles easy axis in a texture and the angular dependence of switching field are two fundamental factors for the distribution function. A technique for determining the switching field distribution curve due to these factors is reported. This technique is performed for textured iron fine particles and samples of CrO 2 and γFe 2O 3 commercial tapes. The distribution differs from a gaussian function. However, the width and the mean switching field equal to twice of the width of d M r/d H curve and the remanent coercivity, respectively. Furthermore, it is shown that the width of the switching field distribution decreases with increasing the degree of easy axis orientation.