230
10 Spintronics Applications
upon the thermal stability of the bits, encoding certain information and recorded on
the hard disk, antiferromagnetically coupled (AFC) media has been realized. For
the purpose of recording or writing the information onto the magnetic hard disk
(Fig. 10.3), a ‘writer’ should be such that it can produce sufficiently high magnetic
field. Such strong magnetic field would be capable to switch the magnetization of a
localized nanosized area of the media to one of two fixed directions. Among those
two directions, one of them represents digit ‘1’ and the other digit ‘0’. Hence, each of
those nanosized localized areas of the hard disk, where information is being stored,
can be considered as one bit (Fig. 10.3). Noteworthy, each bit consists of a number
of partially exchange-coupled magnetic grains.
In early disk drive, while extracting and reproducing the saved information from
the disk, the same write head was employed as the read head. This implies that the
read head detected the signal while passing through the recorded media by measuring
the voltage change, induced across the coils because of the variation of magnetic
flux. Areal density in commercial drives has been found to increase steadily at a
rate of nearly 100% per year and one of the most significant technologies for large
capacity hard disks was the development of magnetic heads (Hirohataa and Yamadab
2020). Vital technology that is essential to increase the memory capacity, while
keeping the physical dimension of the hard disk intact, should be capable to write
and read of recorded information at ultra-high densities. Magnetoresistance is a
physical phenomenon, adopted and applied by magnetic read heads while reading
information. It is the evolution of the magnetoresistance element that in turn causes
the advancement of magnetic heads and thereby breaking the data storage barrier for
hard disks.
10.3.4 Operation of Magnetoresistance Read Heads
Figure 10.4 exhibits schematic representation of a shielded magnetoresistance sensor
used as read head in magnetic hard disk applications. Each bit is recorded in the hard
disk in the form of tiny magnet.
Now, binary bits, i.e., ‘0’ and ‘1’ are stored either in two possible orientations of
magnetizations, namely, left to right and right to left, of tiny magnets. For example,
one may assign ‘0’ to the ‘left to right’ magnetic polarity, whereas ‘1’ to that of ‘right
to left’ magnetic polarity. Flying magnetoresistance sensor, hovering just above such
nano-sized magnetic bits where information is stored, i.e., data storage media, detect
magnetic field lines emanating from those tiny magnets. As a result, they could
identify the direction of polarization of those tiny magnets and thereby the bit encoded
with them. This is the way magnetoresistance sensors act as ‘read head sensor’. As
shown in Fig. 10.4, such read head magnetoresistance sensors are generally shielded,
in order to increase linear resolution and improve high frequency response (Potter
1974).
10 Spintronics Applications
upon the thermal stability of the bits, encoding certain information and recorded on
the hard disk, antiferromagnetically coupled (AFC) media has been realized. For
the purpose of recording or writing the information onto the magnetic hard disk
(Fig. 10.3), a ‘writer’ should be such that it can produce sufficiently high magnetic
field. Such strong magnetic field would be capable to switch the magnetization of a
localized nanosized area of the media to one of two fixed directions. Among those
two directions, one of them represents digit ‘1’ and the other digit ‘0’. Hence, each of
those nanosized localized areas of the hard disk, where information is being stored,
can be considered as one bit (Fig. 10.3). Noteworthy, each bit consists of a number
of partially exchange-coupled magnetic grains.
In early disk drive, while extracting and reproducing the saved information from
the disk, the same write head was employed as the read head. This implies that the
read head detected the signal while passing through the recorded media by measuring
the voltage change, induced across the coils because of the variation of magnetic
flux. Areal density in commercial drives has been found to increase steadily at a
rate of nearly 100% per year and one of the most significant technologies for large
capacity hard disks was the development of magnetic heads (Hirohataa and Yamadab
2020). Vital technology that is essential to increase the memory capacity, while
keeping the physical dimension of the hard disk intact, should be capable to write
and read of recorded information at ultra-high densities. Magnetoresistance is a
physical phenomenon, adopted and applied by magnetic read heads while reading
information. It is the evolution of the magnetoresistance element that in turn causes
the advancement of magnetic heads and thereby breaking the data storage barrier for
hard disks.
10.3.4 Operation of Magnetoresistance Read Heads
Figure 10.4 exhibits schematic representation of a shielded magnetoresistance sensor
used as read head in magnetic hard disk applications. Each bit is recorded in the hard
disk in the form of tiny magnet.
Now, binary bits, i.e., ‘0’ and ‘1’ are stored either in two possible orientations of
magnetizations, namely, left to right and right to left, of tiny magnets. For example,
one may assign ‘0’ to the ‘left to right’ magnetic polarity, whereas ‘1’ to that of ‘right
to left’ magnetic polarity. Flying magnetoresistance sensor, hovering just above such
nano-sized magnetic bits where information is stored, i.e., data storage media, detect
magnetic field lines emanating from those tiny magnets. As a result, they could
identify the direction of polarization of those tiny magnets and thereby the bit encoded
with them. This is the way magnetoresistance sensors act as ‘read head sensor’. As
shown in Fig. 10.4, such read head magnetoresistance sensors are generally shielded,
in order to increase linear resolution and improve high frequency response (Potter
1974).