October 13, 2016

Low energy terahertz radiation could reset computer memory in a picosecond which is 1000 times faster then current memory

A novel, highly energy efficient and ultrafast magnetization control scheme is successfully demonstrated by international team of scientists from the Netherlands, Germany, and Russia. With low-energy terahertz photons the team succeeded to make a magnet wobble in a trillionth of a second.

“Our finding addresses the long-term technological ambition of a direct, high-speed manipulation of magnetic data bits by an electric field, which is achieved at terahertz frequencies in our experiment” says Dr. Rostislav Mikhaylovskiy, the leader of the project at Radboud University in the Netherlands.

The researchers generated very strong pulses of electric field, which cycle within 1 picosecond, i.e. one trillionth of a second. The corresponding frequency is called terahertz which is one trillion of a Hertz. The terahertz electric field is so strong that it can induce a voltage of a million of Volts in a magnet. Thereby it perturbs the orbital motion of the electrons and deflects the direction of the magnetic anisotropy axis. Importantly, this process happens so fast that the magnetization cannot follow this new orientation. Instead, the magnetization starts to wobble around. The amplitude of the magnetization oscillations scales nonlinearly with the driving electric field.

The work could be applicable in recording devices in the near future, using high-frequency transistor amplifiers in combination with tailor-cut near-field antennas. They are working on attaining higher terahertz fields sufficient for the magnetization reversal using terahertz antennas. Another next step is to perform systematic studies of the ultrafast control of the spin-orbit interaction and the magnetic anisotropy in a broad spectral range, to compare the efficiencies of the pumping in the far-, mid-infrared and visible ranges and thus to identify the most efficient, least dissipative, as well as the fastest approach for the manipulation of spins.

Future information technologies, such as ultrafast data recording, quantum computation or spintronics, call for ever faster spin control by light. Intense terahertz pulses can couple to spins on the intrinsic energy scale of magnetic excitations. Here, we explore a novel electric dipole-mediated mechanism of nonlinear terahertz-spin coupling that is much stronger than linear Zeeman coupling to the terahertz magnetic field. Using the prototypical antiferromagnet thulium orthoferrite (TmFeO3), we demonstrate that resonant terahertz pumping of electronic orbital transitions modifies the magnetic anisotropy for ordered Fe3+ spins and triggers large-amplitude coherent spin oscillations. This mechanism is inherently nonlinear, it can be tailored by spectral shaping of the terahertz waveforms and its efficiency outperforms the Zeeman torque by an order of magnitude. Because orbital states govern the magnetic anisotropy in all transition-metal oxides, the demonstrated control scheme is expected to be applicable to many magnetic materials.

Nature Photonics - Nonlinear spin control by terahertz-driven anisotropy fields

11 pages of Supplemental information

SOURCES- Nature Photonics, University of Regensburg

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