GMRShort for giant magnetoresistive, a hard disk drive storage technology. The term is usually referred to in reference to GMR heads. GMR heads are not named "giant" because of their size. The technology is named for the giant magnetoresistive effect, first discovered by two European researchers -- Peter Gruenberg and Albert Fert -- in the late 1980s. While working with large magnetic fields and thin layers of magnetic materials, Gruenberg and Fert noticed very large resistance changes when these materials were subjected to magnetic fields.
Disk drives that are based on GMR head technology use these properties to help control a sensor that responds to very small rotations on the disk. The magnetic rotation yields a very large change in sensor resistance, which in turn provides a signal that can be picked up by the electric circuits in the drive.
GMR heads are made up of four layers of thin material that combine into a single structure:
- Free layer - The sensing layer. The free layer is passed over the surface of the data bits to be read. It is free to rotate in response to the magnetic patterns on the disk.
- Spacer - Typically made from copper, this is a nonmagnetic layer that separates the magnetization of the free and pinned layers.
- Pinned layer - A layer of cobalt material that is held in a fixed magnetic orientation by its proximity to the exchange layer.
- Exchange layer - A layer of antiferromagnetic material that fixes the pinned layer's magnetic orientation.
When the head passes over a magnetic field of one polarity, the electrons on the free layer turn to align with those on the pinned layer, creating a lower resistance in the head structure. When the head passes over a field of opposite polarity, the free layer electrons rotate so that they are not aligned with the electrons on the pinned layer. This causes an increase in the structure's resistance. Because the resistance changes are caused by changes to the spin characteristics of electrons in the free layer, GMR heads are also known as spin valves, a term coined by IBM.
- Check out eWeek's new Research Center, a central and comprehensive library of whitepapers, eBooks, eseminars, webcasts, and more from top industry brands and independent tech journalists »
- Watch Datamation's editor James Maguire moderate roundtable discussions with tech experts from companies such as Accenture, Dell, Blue Jeans Network, Microsoft and more »
If hackers get their hands on your company's data, they can wreak havoc on customer relationships and cause tremendous damage to your brand and... Read More »Windows XP: Move Along, There's Nothing to See Here
After more than 12 years of holding the title of most popular operating system in the world, Windows XP is taking center stage for its final... Read More »Report: The Role of Big Data in the Marketing Industry
According to a new study from Infogroup Targeting Solutions, we can expect to see companies spend heavily on big data marketing initiatives in... Read More »
Creating desktop shortcuts to a websites is useful. When you double-click the icon from your desktop it automatically launches the browser and... Read More »Flash Data Storage Vendor Trends
Although it is almost impossible to keep up with the pace of ongoing product releases, here are three recent highlights in the flash data storage... Read More »15 Important Big Data Facts for IT Professionals
Keeping track of big data trends, research and statistics gives IT professionals a solid foundation to plan big data projects. Here are 15... Read More »