Dilute ferromagnetic semiconductors: Physics and spintronic structures (1307.3429v3)

Abstract: 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, V_2-VI_3, IV-VI, 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 non-trivial 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.

• The paper demonstrates that controlled Mn doping and hole-mediated ferromagnetism enable robust spin order in (Ga,Mn)As thin films.
• The paper details molecular beam epitaxy and annealing methods as key techniques to optimize material growth and stabilize magnetic properties.
• The paper highlights spintronic applications by discussing device innovations like magnetic tunnel junctions and spin transistors, while addressing challenges for room-temperature operation.

Overview of "Dilute Ferromagnetic Semiconductors: Physics and Spintronic Structures"

This paper provides an extensive review of progress in understanding dilute ferromagnetic semiconductors (DFS), specifically those with manganese (Mn) as the magnetic constituent. The primary focus is to discuss how these materials, such as (Ga,Mn)As, are pioneering spintronic technologies by leveraging the unique physics of semiconductor ferromagnetism. The discussions are framed around empirical studies of spintronic devices, highlighting the influence of Mn doping and hole-mediated ferromagnetism.

Key Findings and Discussions

The paper maps the landscape of DFS research, detailing experimental observations and theoretical interpretations. Here are the main aspects covered:

1. Material Properties and Growth Techniques:
   • Thin films and quantum structures with Mn ions exhibit unique ferromagnetic characteristics due to the hole-mediated ferromagnetic order which persists up to temperatures as high as 190 K in certain cases like (Ga,Mn)As. The paper discusses methods such as molecular beam epitaxy (MBE), which are crucial in bypassing Mn solubility limits and optimizing material properties.
2. Spin Orders and Their Control Mechanisms:
   • The role of Mn doping level in achieving desirable spintronic functionalities is heavily emphasized. Enhanced magnetization and ferromagnetic behavior are linked to controlled Mn distribution and hole concentration. Post-growth modifications like annealing are shown to alter Mn interstitial positioning, reducing compensating effects and stabilizing the ferromagnetic order.
3. Carrier and Spin Interactions:
   • Addressing the interplay between electronic and magnetic properties, the paper discusses how efficient spin injection and manipulation hinge on carrier concentration and spin-orbit coupling. The intricate balance of these interactions defines the ferromagnetic phase boundaries and spin dynamics within semiconductors.
4. Theoretical Modeling:
   • A significant section of the paper is dedicated to the theoretical framework underpinning these phenomena – the $p$-$d$ Zener model. Through meticulous parameterization, the model offers predictions on Curie temperatures, anisotropies, and spin interactions, aligning theoretical insights with empirical observations.
5. Spintronic Devices and Applications:
   • The functionalities of DFSs are showcased through devices like magnetic tunnel junctions (MTJs) and spin transistors. The paper discusses the prospects and challenges of integrating these materials into practical spintronic applications, addressing current-induced magnetization switching and coherent spin control by electric fields or light.
6. Remaining Challenges and Future Prospects:
   • Challenges originate from complexities like disorder effects, Anderson-Mott localization, and self-compensation. The quest for room-temperature ferromagnetism continues with speculations on exploring other compounds and new physics, such as those seen in topological insulators and Heusler compounds.

Implications for Spintronics and Beyond

The findings reiterate the DFS's pivotal role in advancing semiconductor-based spintronics. The demonstrated control over magnetization through alloy composition, strain, electric fields, and light is profound, paving the way for novel device functionalities. The interplay of theory and experiment highlighted in the review solidifies our understanding of DFSs and guides ongoing efforts to reach higher operational temperatures and realize commercial spintronic devices.

In summary, this paper not only consolidates current knowledge but also fosters future research directions that aim to harness the full potential of DFSs in a variety of technological applications spanning information technology, storage, and sensing.