The recording of 'information on the surface of the support ferromagnetic basically consists in the transfer of a particular towards the magnetization of a number of Weiss domains.
The number of Weiss domains that constitute a single bit multiplied by the extension mean surface area compared to the available storage, provide the density d 'information (bits per square inch). So
cram a larger amount of data on the same disc requires a reduction in the number of domains that define a single bit and / or reduction of the 'area of \u200b\u200ba single magnetic domain.
's continuing development of hard drive technology has brought us close to the lower limit now tolerable: when in fact the number of domains that define a single bit has been approached to 'unity and their area of' order of a few square nanometers, the 'thermal energy system has become comparable to the' magnetic energy and just a short time have to reverse the direction of magnetization of the domain (this is a fluctuation) and losing in this way the 'information contained.
Reading of 'information in the past was carried out by magnetic inductive heads, miniature copper coils that can detect the change in the flow of the static magnetic field to pass the head between a bit and the next secondo il principio di induzione magnetica.
L’ evoluzione che la spintronica ha portato nelle case di tutti sono state le testine magnetoresistive, basate su un dispositivo, la spin-valve, in grado di variare resistenza al mutare dell’ intensità del campo magnetico.
Il vantaggio dato da queste testine risiede nella loro sensibilità, migliore rispetto alle vecchie testine induttive, e nella loro dimensione ridottissima, cosa che consente di seguire il passo delle evoluzioni verso il nanometro per quanto riguarda l’ area di un singolo bit. Infine, il prossimo futuro vedrà protagoniste della scena le testine di lettura basate sulle magnetic tunneling junction, MTJ.
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