Interface-Related Magnetic Phenomena in Novel Heterostructures
Magnetic properties of materials relevant to the interface or surface provide a promising artificial material basis for the strategic design of spintronic devices. Giant magnetoresistance (GMR), spin accumulation, and spin transfer torque (STT), etc. are
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Interface-Related Magnetic Phenomena in Novel Heterostructures Tomoyasu Taniyama
Abstract Magnetic properties of materials relevant to the interface or surface provide a promising artificial material basis for the strategic design of spintronic devices. Giant magnetoresistance (GMR), spin accumulation, and spin transfer torque (STT), etc. are typical examples of such interface-related magnetic phenomena. Recent enormous and rapid growth of technology also allows to control magnetization orientation, magnetic phases, and spin polarization by manipulating the interface with an electric field without using either a magnetic field or an electric current. This leads to a drastic reduction in the power consumption. A full understanding of the interface-related magnetic phenomena is thus of crucial importance for the development of a major new direction of less energy dissipative spintronics. In this chapter, selected topics of interface-related magnetic phenomena and the fundamental physics underlying are described, placing a special emphasis on electric-field-induced strain transfer effect on the magnetic properties in multiferroic heterostructures.
Keywords Interface-related magnetic phenomena Spintronic devices Electric-field-induced strain transfer Multiferroic heterostructures
7.1
Introduction
Magnetism is one of the most exciting collective phenomena in condensed matter, attracting a steadily increasing number of researchers from both fundamental and application perspectives. This chapter starts with a brief description of the fundamentals of magnetism [1]. The principal mechanism of magnetism or various magnetic orderings, e.g., ferromagnetism, antiferromagnetism, helimagnetism, spin glass, etc. lies in the exchange interaction between the magnetic moments or spin angular momentums of constituent atoms in a material. Since the exchange T. Taniyama (&) Department of Physics, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8602, Japan e-mail: [email protected] © Springer Nature Singapore Pte Ltd. 2019 Y. Setsuhara et al. (eds.), Novel Structured Metallic and Inorganic Materials, https://doi.org/10.1007/978-981-13-7611-5_7
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interaction Hamiltonian Hex is given by the sum of the scalar product of the neighboring spins (Eq. (7.1)), the exchange interaction determines the relative orientation of the magnetic moments so as to minimize the total exchange energy. X Hex ¼ 2 Jij Si Sj ð7:1Þ \i;j [
where Jij is the exchange constant and Si(j) is the spin angular momentum of an atom labeled by the position i(j). The exchange interaction is also a direct and straightforward consequence of the combination of the Pauli exclusive principles and the Coulomb interaction between electrons, clearly indicating that the geometrical arrangement of the surrounding atomic spins in a material strongly influences the magnetism. It is therefore intuitively understood that magnetic properties are extremely sensitive to the atomic arrangement at the interface, and hence distinct magnetic properti
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