Perpendicular magnetic anisotropy and magneto-optical Kerr effect of MnSbAg alloy films with NiAs structure (original) (raw)
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We have studied the time-scale and temperature dependence of the magnetization reversal in perpendicular magnetic recording media. One of the under-reported phenomena associated with this reversal is the thermal dependence of the squareness of the magnetic hysteresis loop. Understanding this phenomenon is important because the coercive squareness parameter S ء is often used to evaluate the strength of the magnetic exchange-coupling interactions between the grains. In this work, we demonstrate that S ء is a dynamic quantity which depends on the thermal agitation of the magnetization, and it is imperative to take this dependence into account in interpreting magnetic and microstructural effects. Based on the Sharrock model for the dynamic coercivity, we built an expression for the time-scale and temperature dependence of S ء in highly oriented perpendicular magnetic recording media. Fits of experimental data to the resulting expression were then used to extract the intrinsic squareness parameter S int ء which originates in the thermal-independent demagnetization and exchange-interaction effects. S int ء was estimated for two sets of perpendicular recording media samples. For the first set of media samples showing progressively smaller grain sizes, the values of S ء measured at the normal magnetometry time-scales of milliseconds to seconds indicated progressively smaller values. In contrast, the values of the thermal-independent S int ء determined from applying the above model were progressively larger. This discrepancy can only be explained on the basis of progressively stronger intergranular exchange coupling, which is offset by strong thermal effects at small grain sizes. For the second set of media samples with increasingly larger segregant oxide content, progressively smaller values of both S ء and thermal-independent S int ء were observed, thus verifying the strong intergranular segregation effects due to greater nonmagnetic grain boundary phase. The phenomenological model for thermal-independent S int ء will be helpful in interpreting the microstructural and magnetic properties of perpendicular magnetic recording media, especially as thermal effects become important in the approach to areal densities of 1 Tbits/ in 2 .
Magnetisation reversal mechanism in CoCr media for perpendicular magnetic recording
Journal of Magnetism and Magnetic Materials, 1997
In this study Co-Cr thin films with perpendicular anisotropy are investigated. Three films with values for/-/'~ of 11, 90 and 170 kA/m have been selected for this paper. Besides the coercivity several other parameters such as the Ho/l-lk, Cr-segregation, domain structure, column sizes, etc. were studied by VSM, SEM, NMR, MFM, AFM and selective etching. The anomalous Hall effect (AHE) has been used to record the hysteresis curves of submicron Hall crosses. This very sensitive technique in combination with e-beam lithography and ion-beam etching resulted in the recording of AHE hysteresis loops with dimensions of the Hall crosses as small as 0.3 x 0.3 ~tm 2. The AHE loops of three samples, with less than 60 columns, show different micromagnetic properties. Only the sample with H~± = 90 kA/m shows clear steps in the curves above the noise level. The largest steps correspond with the reversal of one column and the total number of steps was five times the number of columns for this sample. The different reversal mechanisms observed by the AHE are related to the differences in structure, coercivity and domain size.
Magnetic Characterization of Perpendicular Recording Media
Ultra-High-Density Magnetic Recording: Storage Materials and Media Designs, G. Varvaro and F. Casoli Eds, Pan Stanford Publishing
Developing a nanostructured material to fit the design criteria for perpendicular magnetic recording (PMR) media requires a multiple approach, which involves the investigation of structural, microstructural and magnetic properties, analytical and numerical simulations as well as recording tests to evaluate the material’s read/write performance. Studying the magnetic properties represents a challenging task as the magnetic behavior of materials for PMR media is governed by a complex interplay among intrinsic material properties, magnetic interactions and various sources of microscopic inhomogeneity, the overall properties being further complicated by thermal effects that lead to time-dependent magnetic phenomena. Moreover, the magnetic behavior of systems with perpendicular anisotropy is significantly affected by the presence of strong demagnetizing fields that, in principle, should be corrected in all magnetic measurements for a proper investigation. This chapter will provide an overview of both basic and advanced magnetic characterization methods, mainly based on magnetometry techniques, commonly used to investigate the magnetic behaviour of materials for PMR media in relation to the requirements for high-density recording. Section I will provide a selection of methodologies for the investigation of granular thin films with perpendicular anisotropy, which are used in currently available PMR media being also at the basis of future recording systems. All the methods discussed in this section are also suitable for the characterization of exchange coupled composite systems and next generation bit patterned magnetic recording media, the analysis of their most relevant magnetic properties being discussed in sections II and III, respectively. Section IV will focus on the energy assisted magnetic recording (EAMR) technology by reporting on some specific measurements needed to verify if a material is able to match the peculiar requirements for the application.
Theoretical Aspects of Perpendicular Magnetic Recording Media
Physica Status Solidi (a), 1991
Contents I. Introduction I. I Definition of "perpendicular magnetic recording" 1.2 History 2. General magnetic conditions for perpendicular magnetic recording 2.1 Continuous rnedia 2.2 Particulate niedia 3. Macroscopic model of stored information patterns 3.1 Fields above the information track 3.2 Readhack voltage 3.3 Stahilitji Cf the stored information 3.4 jrr.ansition shlfi cliiriiig writing 3.5 Inzprovements and limits of the block model 4. Microscopic models 4.1 Early models of the influence of structural pr0pertie.r 4.2 Additional conditions ,for magnetic parameters 4.3 Microstructures of recording f i l m s 4.4 Magnetization reversal in films of dgferent magnetic packing deizsity 4.5 The structure ofjlux transitions and the physical limit of storage densit?, 5. Concluding remarks References. . ') Helmholtzweg 4, 0-6900 Jena, FRG. ') Rue de l'universitk 3-5, F-67084 Strasbourg, France.
Perpendicular magnetic anisotropy and magnetization process in CoFeB/Pd multilayer films
Perpendicular magnetic anisotropy (PMA) and dynamic magnetization reversal process in [CoFeB t nm/Pd 1.0 nm] n (t = 0.4, 0.6, 0.8, 1.0, and 1.2 nm; n = 2 -20) multilayer films have been studied by means of magnetic hysteresis and Kerr effect measurements. Strong and controllable PMA with an effective uniaxial anisotropy up to 7.7×10 6 J.m -3 and a saturation magnetization as low as 200 emu/cc are achieved. Surface/interfacial anisotropy of CoFeB/Pd interfaces, the main contribution to the PMA, is separated from the effective uniaxial anisotropy of the films, and appears to increase with the number of the CoFeB/Pd bilayers. Observation of the magnetic domains during a magnetization reversal process using polar magneto-optical Kerr microscopy shows the detailed behavior of nucleation and displacement of the domain walls.
Journal of Applied Physics, 1988
Perpendicular magnetic anisotropy (PMA) and dynamic magnetization reversal process in [CoFeB t nm/Pd 1.0 nm] n (t = 0.4, 0.6, 0.8, 1.0, and 1.2 nm; n = 2 -20) multilayer films have been studied by means of magnetic hysteresis and Kerr effect measurements. Strong and controllable PMA with an effective uniaxial anisotropy up to 7.7×10 6 Jm −3 and a saturation magnetization as low as 200 emu/cc are achieved. Surface/interfacial anisotropy of CoFeB/Pd interfaces, the main contribution to the PMA, is separated from the effective uniaxial anisotropy of the films, and appears to increase with the number of the CoFeB/Pd bilayers. Observation of the magnetic domains during a magnetization reversal process using polar magneto-optical Kerr microscopy shows the detailed behavior of nucleation and displacement of the domain walls.
Present and future of magnetooptical recording materials and technology
Journal of Alloys and Compounds, 1998
Erasable optical information storage from amorphous rare earth-transition metal (RE-TM) alloys media has led to impressive improvements towards hyper high density recording in the past five years. Write / erase and readout processes are based on light-induced thermomagnetic switching of magnetic domains and magnetooptical (MO) Kerr effect, respectively, in ferrimagnetic films exhibiting a uniaxial magnetic anisotropy. The route towards ultrahigh optical areal densities was open from the beginning of the nineties from two key technologies related to near field optical techniques and RE-TM exchange-coupled bi, tri-and multilayers. The performances of the MO media depend on the types and states of these multilayers with perpendicular or mixed (perpendicular and planar) anisotropies which change with the temperature and the applied field. The development of the thermomagnetooptical materials is discussed with reference to their magnetic and MO properties to increase the density storage.
Magnetic Anisotropy and Coercivity in Magneto-Optical Recording Materials
Journal of the Magnetics Society of Japan, 1999
The perpendicular magnetic anisotropy of both amorphous Tb-Fe and crystalline fcc Pt-rich Co-Pt alloys is enhanced by increasing growth temperature, up to the onset of significant bulk atomic mobility (approximately one third of the melting temperature). High growth temperature also stabilizes these materials against subsequent annealing which tends to eliminate the anisotropy. The dependence on growth temperature can be fit with a two-level systems analysis in which the low energy surface state during growth is anisotropic. The source of this low energy state is suggested to be related to surface segregation for the Co-Pt alloys. The anisotropy for both materials shows very little dependence on substrate type, sample thickness, or details of the deposition such as sputtering or e-beam evaporation. Coercivity on the other hand is extremely dependent on microstructure and hence on details of preparation, substrate type, thickness, and crystallographic orientation. For a-Tb-Fe, the dominant mechanism appears to be domain wall pinning by microstructural defects in the bulk of the film, such as columnar microstructure.