Precessional switching in magnetic memory devices demonstrated by NIST. (News Briefs).A particular type of thin-film magnetic device called a spin-valve can be engineered to have two stable states of electrical resistance Electrical resistance Opposition of a circuit to the flow of electric current. Ohm's law states that the current I flowing in a circuit is proportional to the applied potential difference V. based on the relative magnetization orientation of its ferromagnetic Refers to a material, such as iron and nickel, that can be easily magnetized. See MRAM. layers. This property has motivated a strong interest in using spin-valves as recording bits in non-volatile, magnetic random access memory (MRAM (Magnetic RAM) A non-volatile, random access memory technology that is designed to initially replace flash memory and, potentially, DRAM memory. MRAM uses magnetic, thin film elements on a silicon substrate that can be built on the same chip with the logic circuits. ). A primary technical hurdle is precise control of the switching of individual devices. NIST (National Institute of Standards & Technology, Washington, DC, www.nist.gov) The standards-defining agency of the U.S. government, formerly the National Bureau of Standards. It is one of three agencies that fall under the Technology Administration (www.technology. researchers have been studying the dynamics of magnetization reversal in spin-valves. Devices have sub-micrometer dimensions and are fabricated within a test structure that includes high-bandwidth transmission lines. One line delivers ultra-fast magnetic field pulses to the device. The other line is electrically connected to the device and carries the voltage pulse generated as the device changes state. This voltage pulse serves as a probe of the magnetization dynamics of the device. In a spin-valve, only one ferromagnetic layer, the free layer, responds to external fields. Internal magnetic fields magnetic fields, n.pl the spaces in which magnetic forces are detectable; created by magnetostrictive ultrasonic scalers to cause the tips of instruments such as ultrasonic scalers to vibrate. within the device allow only two stable magnetization directions, 180[degrees], along an easy axis. Current implementation of MRAM requires field pulses applied for 10 ns to 20 ns along either the positive or negative easy axis, depending on the desired state. The NIST scientists have discovered a way to switch the devices using field pulses of less than 300 ps duration directed perpendicular to the easy axis. The magnetization is reversed due to large-angle precessional pre·ces·sion n. 1. The act or state of preceding; precedence. 2. Physics The motion of the axis of a spinning body, such as the wobble of a spinning top, when there is an external force acting on the axis. 3. motion. For longer duration pulses, the device does not switch because the magnetization rotates back to its initial direction while the pulse is on. Precessional switching requires only a single polarity pulse applied perpendicular to the device easy axis, which results in a toggle To alternate back and forth between two states. toggle - To change a bit from whatever state it is in to the other state; to change from 1 to 0 or from 0 to 1. This comes from "toggle switches", such as standard light switches, though the word "toggle" actually refers to operation of the magnetic state of the device. This is a simpler and more efficient bit-setting operation than using pulsed fields along the easy axis which requires longer pulses in both directions. CONTACT: Stephen Russek, (304) 497-5097; russek@boulder.nist.gov. |
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