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Basics of Nanothin Film Magnetism
Published in Evgeny Y. Tsymbal, Žutić Igor, Spintronics Handbook: Spin Transport and Magnetism, Second Edition, 2019
Bretislav Heinrich, Pavlo Omelchenko, Erol Girt
To increase the recording density of magnetic media, the size of magnetic grains has to be reduced. This ensures that there is a large enough number of grains per bit to achieve the desired signal-to-noise ratio (SNR). From statistical arguments, the SNR is directly related to the number of grains/bit. The stored bits must be thermally stable. Thus, a decrease of grain volume, V, requires a proportional increase in K of grains in order to keep KV/kBT>40 [71], where T is the temperature at which hard drives operate, and kB is the Boltzmann constant. If K of magnetic grains increases, the recording head field has to also increase to reverse magnetic grains in a bit. Since the maximum field that can be generated by recording head is limited, it would follow that the increase of magnetic recording areal density is also limited. This trilemma correlates three recording media parameters, SNR, thermal stability and writability.
Magnetic Nanoparticle for Information Storage Applications
Published in Claudia Altavilla, Enrico Ciliberto, Inorganic Nanoparticles: Synthesis, Applications, and Perspectives, 2017
The standard design for hard disk drives, throughout the vast majority their existence and until recently, has been the longitudinal recording system (Piramanayagam and Srinivasan 2009). The media in longitudinal recording contains grains whose magnetic moments lie in the plane of the disk. The system also contains a recording head composed of a separate read and write element, which flies in close proximity to a recording medium. The inductive write element records the data in horizontal magnetization patterns (Figure 3.2a). The information is then read back with a giant magnetoresistive (GMR) read element by measuring the stray magnetic field from the transitions between regions of opposite magnetization. Finally, a signal processing unit transforms the analog read back signal into a stream of data bits. The media for these longitudinal systems is fabricated in the form of granular thin films, which are usually deposited by dc magnetron sputtering and consist of a CoPtCrX alloy (X = B, Ta). Along with the recording layer, there are several other layers that make up the media and all are in a polycrystal-line state. The extra layers help to nucleate grain growth, control grain size and shape, and help in reducing stray magnetic fields and interactions from the read and write elements.
Miscellaneous Sensors
Published in Clarence W. de Silva, Sensor Systems, 2016
Many types of sensors and transducers that are based on optical methods do indeed employ optical coupling (e.g., optical encoders, fiber-optic tactile sensors). Optical sensors are widely used in industry for parts counting, parts detection, and level detection. In these sensors, a light beam is projected from a source to a photodetector, both units being stationary. An interruption of the beam through the passage of a part will generate a pulse at the detector, and this pulse is read by a counter or a parts detector (see Chapter 11). Furthermore, if the light beam is located horizontally at a required height, its interruption when the material filled into a container reaches that level may be used for filling control in the packaging industry. Note that the light source and the sensor can be located within a single package if a mirror is used to reflect light from the source back onto the detector. Further applications include computer disk drive systems, for example, to detect the write protect notch as well as the position of the recording head.
Characterisation of electroplated Ni45Fe55 thin films on n-Si (111)
Published in Surface Engineering, 2019
A. Chenna, N. Benbrahim, L. Hamadou, S. Boudinar, A. Kadri, E. Chainet, Y. Dahmane
The need for recording heads to write on highly coercive media at high frequencies created additional requirements for new soft magnetic materials with higher magnetic moments. A magnetic recording head should preferably have a low coercivity, high magnetic moment, large electrical resistance, no internal stresses and high corrosion resistance. As a consequence, a combination of suitable magnetic properties with excellent corrosion behaviour would improve the reliability of the devices. Corrosion resistance is considered as an indication of the durability of the film material [1,2]. Due to this combination of properties, NiFe film seems to be an appropriate candidate to meet these technological demands. Since it is possible to change its magnetic properties by controlling its form and composition, different studies were carried out on the FexNi1−x alloy, including thin films[3–7] and nanowires or nanotubes [8,9],