Abstract-Large terahertz magnetization response in ferromagnetic nanoparticles

Applied Physics Letters

Tomoaki Ishii,  Hiromichi Yamakawa, Toshiki Kanaki, Tatsuya Miyamoto, Noriaki Kida,   Hiroshi Okamoto, Masaaki Tanaka,  Shinobu Ohya,

https://aip.scitation.org/doi/10.1063/1.5088227

Ultra-fast coherent magnetization reversal, which is indispensable for high-speed spintronic devices, is expected to be realized by irradiation with a nearly monocyclic terahertz pulse. In this letter, using MnAs ferromagnetic nanoparticles embedded in a GaAs host matrix, we observe a large modulation up to 20% of the magnetization of these nanoparticles with terahertz pump pulse irradiation. This modulation ratio is the largest value ever reported for terahertz magnetization modulation. We reveal that the modulation is induced by the electric-field component of the terahertz pulse via spin-carrier interactions. Ferromagnetic nanoparticle systems are promising, and material designing is the key for ultrafast magnetization reversal using terahertz pulses.

Abstract-Ultrafast magnetization modulation induced by the electric field component of a terahertz pulse in a ferromagnetic-semiconductor thin film

Tomoaki Ishii, Hiromichi Yamakawa, Toshiki Kanaki, Tatsuya Miyamoto, Noriaki Kida, Hiroshi Okamoto, Masaaki Tanaka,  Shinobu Ohya

https://www.nature.com/articles/s41598-018-25266-2


High-speed magnetization control of ferromagnetic films using light pulses is attracting considerable attention and is increasingly important for the development of spintronic devices. Irradiation with a nearly monocyclic terahertz pulse, which can induce strong electromagnetic fields in ferromagnetic films within an extremely short time of less than ~1 ps, is promising for damping-free high-speed coherent control of the magnetization. Here, we successfully observe a terahertz response in a ferromagnetic-semiconductor thin film. In addition, we find that a similar terahertz response is observed even in a non-magnetic semiconductor and reveal that the electric-field component of the terahertz pulse plays a crucial role in the magnetization response through the spin-carrier interactions in a ferromagnetic-semiconductor thin film. Our findings will provide new guidelines for designing materials suitable for ultrafast magnetization reversal.

Abstract-Ultrafast modulation of polarization amplitude by terahertz fields in electronic-type organic ferroelectrics

• Tatsuya Miyamoto,
• Hiroyuki Yada,
• Hiromichi Yamakawa
• & Hiroshi Okamoto

• http://www.nature.com/ncomms/2013/131017/ncomms3586/full/ncomms3586.html

Ferroelectrics sometimes show large electro-optical and non-linear optical effects, available for polarization rotation and frequency conversion of light, respectively. If the amplitude of ferroelectric polarization is modulated in the picosecond time domain, terahertz repetition of optical switching via electro-optical and non-linear optical effects would be achieved. Here we show that polarization amplitude can be rapidly modulated by a terahertz electric field in an organic ferroelectric, tetrathiafulvalene-p-chloranil (TTF-CA). In this compound, alternately stacked donor (TTF) and acceptor (CA) molecules are dimerized via the spin-Peierls mechanism, and charge transfer within each dimer results in a new type of ferroelectricity called electronic-type ferroelectricity. Using a terahertz field, the intradimer charge transfer is strongly modulated, producing a subpicosecond change in the macroscopic polarization, which is demonstrated by transient reflectivity and second-harmonic generation measurements. Subsequently, coherent oscillation of the dimeric molecular displacements occur, which is explained by the modulation of the spin moment of each molecule.