The interaction of subpicosecond laser pulses with magnetically ordered materials has developed into a fascinating research topic in modern magnetism. From the discovery of subpicosecond demagnetization over a decade ago to the recent demonstration of magnetization reversal by a single 40 fs laser pulse, the manipulation of magnetic order by ultrashort laser pulses has become a fundamentally challenging topic with a potentially high impact for future spintronics, data storage and manipulation, and quantum computation. Understanding the underlying mechanisms implies understanding the interaction of photons with charges, spins, and lattice, and the angular momentum transfer between them. This paper will review the progress in this field of laser manipulation of magnetic order in a systematic way. Starting with a historical introduction, the interaction of light with magnetically ordered matter is discussed. By investigating metals, semiconductors, and dielectrics, the roles of nearly free electrons, charge redistributions, and spin-orbit and spin-lattice interactions can partly be separated, and effects due to heating can be distinguished from those that are not. It will be shown that there is a fundamental distinction between processes that involve the actual absorption of photons and those that do not. It turns out that for the latter, the polarization of light plays an essential role in the manipulation of the magnetic moments at the femtosecond time scale. Thus, circularly and linearly polarized pulses are shown to act as strong transient magnetic field pulses originating from the nonabsorptive inverse Faraday and inverse Cotton-Mouton effects, respectively. The recent progress in the understanding of magneto-optical effects on the femtosecond time scale together with the mentioned inverse, optomagnetic effects promises a bright future for this field of ultrafast optical manipulation of magnetic order or femtomagnetism.

/pdf/ultrafast-optical-manipulation-of-magnetic-order-2ms2t5k1zo.pdf

Ultrafast optical manipulation of magnetic order

This review compiles results of experimental and theoretical studies on thin films and quantum structures of semiconductors with randomly distributed Mn ions, which exhibit spintronic functionalities associated with collective ferromagnetic spin ordering. Properties of p-type Mn-containing III-V as well as II-VI, IV-VI, V-2 -VI3, I-II-V, and elemental group IV semiconductors are described, paying particular attention to the most thoroughly investigated system (Ga, Mn)As that supports the hole-mediated ferromagnetic order up to 190 K for the net concentration of Mn spins below 10%. Multilayer structures showing efficient spin injection and spin-related magnetotransport properties as well as enabling magnetization manipulation by strain, light, electric fields, and spin currents are presented together with their impact on metal spintronics. The challenging interplay between magnetic and electronic properties in topologically trivial and nontrivial systems is described, emphasizing the entangled roles of disorder and correlation at the carrier localization boundary. Finally, the case of dilute magnetic insulators is considered, such as (Ga, Mn)N, where low-temperature spin ordering is driven by short-ranged superexchange that is ferromagnetic for certain charge states of magnetic impurities.

Dilute ferromagnetic semiconductors: Physics and spintronic structures

This article reviews the current status of spin dynamics in semiconductors which has achieved a lot of progress in the past years due to the fast growing field of semiconductor spintronics. The primary focus is the theoretical and experimental developments of spin relaxation and dephasing in both spin precession in time domain and spin diffusion and transport in spacial domain. A fully microscopic many-body investigation on spin dynamics based on the kinetic spin Bloch equation approach is reviewed comprehensively.

Spin dynamics in semiconductors

Magnetic two-dimensional materials have attracted considerable attention for their significant potential application in spintronics. In this study, we present a high-quality Fe-doped SnS2 monolayer exfoliated using a micromechanical cleavage method. Fe atoms were doped at the Sn atom sites, and the Fe contents are ∼2.1%, 1.5%, and 1.1%. The field-effect transistors based on the Fe0.021Sn0.979S2 monolayer show n-type behavior and exhibit high optoelectronic performance. Magnetic measurements show that pure SnS2 is diamagnetic, whereas Fe0.021Sn0.979S2 exhibits ferromagnetic behavior with a perpendicular anisotropy at 2 K and a Curie temperature of ~31 K. Density functional theory calculations show that long-range ferromagnetic ordering in the Fe-doped SnS2 monolayer is energetically stable, and the estimated Curie temperature agrees well with the results of our experiment. The results suggest that Fe-doped SnS2 has significant potential in future nanoelectronic, magnetic, and optoelectronic applications. 2D materials can be doped with magnetic atoms in order to boost their potential applications in spintronics. Here, the authors fabricate Fe-doped SnS2 monolayers and show that Fe0.021Sn0.979S2 exhibits ferromagnetic behaviour with perpendicular anisotropy at 2 K, and a Curie temperature of 31 K.

A two-dimensional Fe-doped SnS2 magnetic semiconductor.

The control and manipulation of the electron spin in semiconductors is central to spintronics, which aims to represent digital information using spin orientation rather than electron charge. Such spin-based technologies may have a profound impact on nanoelectronics, data storage, and logic and computer architectures. Recently it has become possible to induce and detect spin polarization in otherwise non-magnetic semiconductors (gallium arsenide and silicon) using all-electrical structures, but so far only at temperatures below 150 K and in n-type materials, which limits further development. Here we demonstrate room-temperature electrical injection of spin polarization into n-type and p-type silicon from a ferromagnetic tunnel contact, spin manipulation using the Hanle effect and the electrical detection of the induced spin accumulation. A spin splitting as large as 2.9 meV is created in n-type silicon, corresponding to an electron spin polarization of 4.6%. The extracted spin lifetime is greater than 140 ps for conduction electrons in heavily doped n-type silicon at 300 K and greater than 270 ps for holes in heavily doped p-type silicon at the same temperature. The spin diffusion length is greater than 230 nm for electrons and 310 nm for holes in the corresponding materials. These results open the way to the implementation of spin functionality in complementary silicon devices and electronic circuits operating at ambient temperature, and to the exploration of their prospects and the fundamental rules that govern their behaviour.

http://absimage.aps.org/image/MAR10/MWS_MAR10-2009-008352.pdf

Electrical creation of spin polarization in silicon at room temperature

We demonstrate by magneto-transport measurements that a Curie temperature as high as 200 K can be obtained in nanostructures of (Ga,Mn)As. Heavily Mn-doped (Ga,Mn)As films were patterned into nanowires and then subject to low-temperature annealing. Resistance and Hall effect measurements demonstrated a consistent increase of T(C) with decreasing wire width down to about 300 nm. This observation is attributed primarily to the increase of the free surface in the narrower wires, which allows the Mn interstitials to diffuse out at the sidewalls, thus enhancing the efficiency of annealing. These results may provide useful information on optimal structures for (Ga,Mn)As-based nanospintronic devices operational at relatively high temperatures.

Enhancing the Curie Temperature of Ferromagnetic Semiconductor (Ga,Mn)As to 200 K via Nanostructure Engineering

In this review article, we review the progress made in the past several years mainly regarding the efforts devoted to increasing the Curie temperature (TC) of (Ga,Mn)As, which is most widely considered as the prototype ferromagnetic semiconductor. Heavy Mn doping, nanostructure engineering and post-growth annealing which increase TC are described in detail.

https://static.springer.com/sgw/documents/1387709/application/pdf/Enhancement+of+the+Curie+temperature+of+ferromagnetic+semiconductor+%28Ga%2CMn%29As+.pdf

Enhancement of the Curie temperature of ferromagnetic semiconductor (Ga,Mn)As

Electron spin relaxation and related mechanisms in heavily Mn-doped (Ga,Mn)As are studied by performing time-resolved magneto-optical Kerr effect measurements. At low temperature, s-d exchange scattering dominates electron spin relaxation, whereas the Bir–Aronov–Pikus mechanism and Mn impurity scattering play important roles at high temperature. The temperature-dependent spin relaxation time exhibits an anomaly around the Curie temperature (Tc) that implies that thermal fluctuation is suppressed by short-range correlated spin fluctuation above Tc.

Electron spin dynamics in heavily Mn-doped (Ga,Mn)As

The spin lifetime and Hanle signal amplitude dependence on bias current has been investigated in insulating Al$_{0.3}$Ga$_{0.7}$As:Si using a three-terminal Hanle effect geometry. The amplitudes of the Hanle signals are much larger for forward bias than for reverse bias, although the spin lifetimes found are statistically equivalent. The spin resistance-area product shows a strong increase with bias current for reverse bias and small forward bias until 150 $\mu$A, beyond which a weak dependence is observed. The spin lifetimes diminish substantially with increasing bias current. The dependence of the spin accumulation and lifetime diminish only moderately with temperature from 5 K to 30 K.

Bias current dependence of the spin lifetime in insulating Al$_{0.3}$Ga$_{0.7}$As

The spin lifetime and Hanle signal amplitude dependence on bias current has been investigated in insulating Al0.3Ga0.7As:Si using a three-terminal Hanle effect geometry. The amplitudes of the Hanle signals are much larger for forward bias than for reverse bias, although the spin lifetimes found are statistically equivalent. The spin resistance-area product shows a strong increase with bias current for reverse bias and small forward bias until 150 μA, beyond which a weak dependence is observed. The spin lifetimes diminish substantially with increasing bias current. The dependence of the spin accumulation and lifetime diminish only moderately with temperature from 5 K to 30 K.

Bias current dependence of the spin lifetime in insulating Al0.3Ga0.7As

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