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Chapter 20: Problem 27

Briefly explain the manner in which information is stored magnetically.

Short Answer

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Question: Explain the key concepts involved in magnetic storage and how data is written and read from magnetic storage devices. Answer: Magnetic storage is a non-volatile method that relies on manipulating the magnetic properties of materials to store information. Key concepts involved in magnetic storage include magnetism, magnetic domains, and hysteresis. Data is stored by changing the magnetization of small regions, called magnetic bits, that can represent binary data (either "0" or "1"). Writing data is done using a magnetic write head that generates a local magnetic field, which changes the magnetization direction of the bits. Reading data is accomplished with a magnetic read head, which measures the changes in the magnetic field without altering the magnetization, and converts these changes into an electrical signal that represents binary data.

Step by step solution

01

Introduction to Magnetic Storage

Magnetic storage is a method of storing information by manipulating the magnetic properties of a material. This is often used as a non-volatile storage method, meaning the data is retained even when the device is not powered. Common examples of magnetic storage devices include hard disk drives (HDDs) and magnetic tapes.
02

Magnetism Basis

Magnetic storage relies on the phenomenon of magnetism, which is based on the behavior of charged particles, like electrons, in materials. Materials have a property called magnetization, which is the measure of the net magnetic moment resulting from the alignment of the magnetic dipoles, such as electrons. When these magnetic moments are aligned, they create a measurable magnetic field.
03

Magnetic Domains and Hysteresis

The key concept in magnetic storage is the existence of magnetic domains, which are regions within a magnetic material where the magnetic moments tend to align in the same direction. By applying an external magnetic field, the alignment of the magnetic moments in these domains can be changed. The relationship between the applied external magnetic field and the magnetization of the material is described by the hysteresis loop.
04

Storing Data in Magnetic Storage Devices

Data is stored in magnetic storage devices by changing the magnetization of small regions (known as magnetic bits) on a magnetic medium, such as a hard disk platter or magnetic tape. Each magnetic bit can have one of two possible magnetization states, representing a binary digit (either "0" or "1").
05

Writing Data to Magnetic Storage

Writing data to a magnetic storage device involves changing the magnetization direction of magnetic bits with a magnetic write head. The write head generates a local magnetic field that is strong enough to overcome the coercivity (resistance to change the magnetization) of the magnetic medium. By controlling the direction and duration of the magnetic field generated by the write head, the magnetization direction of the bits can be set to represent the desired data.
06

Reading Data from Magnetic Storage

To read data from a magnetic storage device, a magnetic read head is used to detect the magnetization direction of the magnetic bits. The read head does not change the magnetization of the bits, but instead measures the changes in the magnetic field as it moves across the magnetic medium. These changes in magnetic field are then converted to an electrical signal, which can be interpreted as binary data.
07

Summary

Magnetic storage is a non-volatile method of storing information by manipulating the magnetic properties of materials. It involves dividing the magnetic medium into small regions, or bits, and aligning the magnetic moments in these bits to represent binary data. Writing data involves changing the magnetization direction of the bits using a magnetic write head, and reading data is done by measuring the magnetic field changes with a magnetic read head.

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Most popular questions from this chapter

The chemical formula for copper ferrite may be written as \(\left(\mathrm{CuFe}_{2} \mathrm{O}_{4}\right)_{8}\) because there are eight formula units per unit cell. If this material has a saturation magnetization of \(1.35 \times 10^{5} \mathrm{~A} / \mathrm{m}\) and a density of \(5.40 \mathrm{~g} / \mathrm{cm}^{3}\), estimate the number of Bohr magnetons associated with each \(\mathrm{Cu}^{2+}\) ion.

Cite the differences between type I and type II superconductors.

It is possible to express the magnetic susceptibility \(\chi_{m}\) in several different units. For the discussion in this chapter, \(\chi_{m}\) is used to designate the volume susceptibility in SI units-that is, the quantity that gives the magnetization per unit volume \(\left(\mathrm{m}^{3}\right)\) of material when multiplied by \(H\). The mass susceptibility \(\chi_{m}(\mathrm{~kg})\) yields the magnetic moment (or magnetization) per kilogram of material when multiplied by \(H\); similarly, the atomic susceptibility \(\chi_{m}\) (a) gives the magnetization per kilogram-mole. The last two quantities are related to \(\chi_{m}\) through the following relationships: $$ \begin{aligned} &\chi_{m}=\chi_{m}(\mathrm{~kg}) \times \text { mass density }\left(\text { in } \mathrm{kg} / \mathrm{m}^{3}\right) \\ &\chi_{m}(a)=\chi_{m}(\mathrm{~kg}) \times \text { atomic weight }(\text { in } \mathrm{kg}) \end{aligned} $$ When using the cgs-emu system, comparable parameters exist that may be designated by \(\chi_{m}^{\prime}\), \(\chi_{m}^{\prime}(\mathrm{g})\), and \(\chi_{m}^{\prime}(a) ;\) the \(\chi_{m}\) and \(\chi_{m}^{\prime}\) are related in accordance with Table 20.1. From Table 20.2, \(\chi_{m}\) for copper is \(-0.96 \times 10^{-5}\); convert this value into the other five susceptibilities.

The formula for samarium iron garnet \(\left(\mathrm{Sm}_{3} \mathrm{Fe}_{5} \mathrm{O}_{12}\right)\) may be written in the form \(\mathrm{Sm}_{3}^{c} \mathrm{Fe}_{2}^{a} \mathrm{Fe}_{3}^{d} \mathrm{O}_{12}\), where the superscripts \(a, c\), and \(d\) represent different sites on which the \(\mathrm{Sm}^{3+}\) and \(\mathrm{Fe}^{3+}\) ions are located. The spin magnetic moments for the \(\mathrm{Sm}^{3+}\) and \(\mathrm{Fe}^{3+}\) ions positioned in the \(a\) and \(c\) sites are oriented parallel to one another and antiparallel to the \(\mathrm{Fe}^{3+}\) ions in \(d\) sites. Compute the number of Bohr magnetons associated with each \(\mathrm{Sm}^{3+}\) ion, given the following information: (1) each unit cell consists of eight formula \(\left(\mathrm{Sm}_{3} \mathrm{Fe}_{5} \mathrm{O}_{12}\right)\) units; (2) the unit cell is cubic with an edge length of \(1.2529 \mathrm{~nm} ;\) (3) the saturation magnetization for this material is \(1.35 \times 10^{5} \mathrm{~A} / \mathrm{m} ;\) and (4) there are 5 Bohr magnetons associated with each \(\mathrm{Fe}^{3+}\) ion.

An iron bar magnet having a coercivity of \(7000 \mathrm{~A} / \mathrm{m}\) is to be demagnetized. If the bar is inserted within a cylindrical wire coil \(0.25 \mathrm{~m}\) long and having 150 turns, what electric current is required to generate the necessary magnetic field?
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