In this chapter, we will restrict our attention to the ferrites and a few other closely related materials. The great interest in ferrites stems from their unique combination of a spontaneous magnetization and a high electrical resistivity. The observed magnetization results from the difference in the magnetizations of two non-equivalent sub-lattices of the magnetic ions in the crystal structure. Materials of this type should strictly be designated as “ferrimagnetic” and in some respects are more closely related to anti-ferromagnetic substances than they are to ferromagnetics in which the magnetization results from the parallel alignment of all the magnetic moments present. We shall not adhere to this special nomenclature except to emphasize effects, which are due to the existence of the sub-lattices.

Ferromagnetic materials

Solid-state electronics

Oxides have become a key ingredient for new concepts of electronic devices. To a large extent, this is due to the profusion of new physics and novel functionalities arising from ultrathin oxide films and at oxide interfaces. We present here a perspective on selected topics within this vast field and focus on two main issues. The first part of this review is dedicated to the use of ultrathin films of insulating oxides as barriers for tunnel junctions. In addition to dielectric non-magnetic epitaxial barriers, which can produce tunneling magnetoresistances in excess of a few hundred percent, we pay special attention to the possibility of exploiting the multifunctional character of some oxides in order to realize ‘active’ tunnel barriers. In these, the conductance across the barrier is not only controlled by the bias voltage and/or the electrodes magnetic state, but also depends on the barrier ferroic state. Some examples include spin-filtering effects using ferro- and ferrimagnetic oxides, and the possibili...

Ultrathin oxide films and interfaces for electronics and spintronics

Ferrite nanoparticles (FNPs) have attracted a great interest due to their wide applications in several areas such as biomedical, wastewater treatment, catalyst and electronic device. This review focuses on the synthesis, characterisation and application of FNPs in electronic device with more emphasis on the recently published works. The most commonly used synthesis techniques along with their advantages and limitations are discussed. The available characterisation techniques and their application in electronic materials such as sensors and biosensors, energy storage, microwave device, electromagnetic interference shielding and high-density recording media are briefly reviewed.

Ferrite nanoparticles: Synthesis, characterisation and applications in electronic device

Application of spinel ferrite nanoparticles in water and wastewater treatment: A review

We report detailed studies on ferromagnet-superconductor bilayer structures. Epitaxial bilayer structures of half metal-colossal magnetoresistive (HMCMR) ${\mathrm{La}}_{2∕3}{\mathrm{Ca}}_{1∕3}{\mathrm{MnO}}_{3}$ and high-${T}_{c}$ superconducting (HTSC) ${\mathrm{YBa}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{7\ensuremath{-}\ensuremath{\delta}}$ are grown on ${\mathrm{SrTiO}}_{3}\phantom{\rule{0.3em}{0ex}}(100)$ single-crystalline substrates using pulsed laser deposition. Magnetization $M(T)$ measurements show the coexistence of ferromagnetism and superconductivity in these structures at low temperatures. Using the HMCMR layer as an electrode for spin polarized electrons, we discuss the role of spin polarized self injection into the HTSC layer. The experimental results are in good agreement with a presented theoretical estimation, where the spin diffusion length ${\ensuremath{\xi}}_{\mathrm{FM}}$ is found to be in the range of ${\ensuremath{\xi}}_{\mathrm{FM}}\ensuremath{\approx}10\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$.

Ferromagnetic/superconducting bilayer structure: A model system for spin diffusion length estimation

The interaction between electrons and phonons is important for many materials properties. The finding that phonon modes of a superconducting thin film can influence the properties of an adjacent normal conductor, even over comparatively long distances, suggests new ways of controlling electron–phonon interactions. The electron–phonon interaction is of central importance for the electrical and thermal properties of solids, and its influence on superconductivity, colossal magnetoresistance and other many-body phenomena in correlated-electron materials is the subject of intense research at present. However, the non-local nature of the interactions between valence electrons and lattice ions, often compounded by a plethora of vibrational modes, presents formidable challenges for attempts to experimentally control and theoretically describe the physical properties of complex materials. Here we report a Raman scattering study of the lattice dynamics in superlattices of the high-temperature superconductor YBa2Cu3O7 (YBCO) and the colossal-magnetoresistance compound La2/3Ca1/3MnO3 that suggests a new approach to this problem. We find that a rotational mode of the MnO6 octahedra in La2/3Ca1/3MnO3 experiences pronounced superconductivity-induced line-shape anomalies, which scale linearly with the thickness of the YBCO layers over a remarkably long range of several tens of nanometres. The transfer of the electron–phonon coupling between superlattice layers can be understood as a consequence of long-range Coulomb forces in conjunction with an orbital reconstruction at the interface. The superlattice geometry thus provides new opportunities for controlled modification of the electron–phonon interaction in complex materials.

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Long-range transfer of electron–phonon coupling in oxide superlattices

We report on a systematic study of strain effects on the transport properties and the ferromagnetic transition temperature ${T}_{c}$ of high-quality ${\mathrm{La}}_{0.9}{\mathrm{Sr}}_{0.1}{\mathrm{MnO}}_{3}$ thin films epitaxially grown on (100) ${\mathrm{SrTiO}}_{3}$ substrates. Both the magnetization and the resistivity are critically dependent on the film thickness. ${T}_{c}$ is enhanced with decreasing the film thickness due to the compressive stain produced by lattice mismatch. The resistivity above 165 K of the films with various thicknesses is consistent with small polaronic hopping conductivity. The polaronic formation energy ${E}_{P}$ is reduced with the decrease of film thickness. We found that the strain dependence of ${T}_{c}$ mainly results from the strain-induced electron-phonon coupling. The strain effect on ${E}_{P}$ is in good agreement with the theoretical predictions.

Strain effect on electronic transport and ferromagnetic transition temperature in La 0.9 Sr 0.1 MnO 3 thin films

Investigation of the structural, optical and magnetic properties of CuO/CuFe2O4 nanocomposites synthesized via simple microemulsion method

The magnetic properties of heterostructures of high-temperature superconducting $\mathrm{Y}{\mathrm{Ba}}_{2}{\mathrm{Cu}}_{3}{\mathrm{O}}_{7\ensuremath{-}\ensuremath{\delta}}$ and highly spin polarized, ferromagnetic ${\mathrm{La}}_{2∕3}{\mathrm{Ca}}_{1∕3}\mathrm{Mn}{\mathrm{O}}_{3}$ that are electronically decoupled by a thin $\mathrm{Sr}\mathrm{Ti}{\mathrm{O}}_{3}$ layer are investigated by means of SQUID magnetometry. Below the transition temperature of the superconducting component the detected signal is a measure for the critical current in the superconductor. The obtained magnetic hysteresis loops at low temperatures exhibit a substantial asymmetry with respect to $H=0$. This can be understood in terms of pinning of flux lines in the superconducting film due to magnetic interaction with the ferromagnetic manganite layer.

S. Soltan

Papers

Ferromagnetic/superconducting bilayer structure: A model system for spin diffusion length estimation

Long-range transfer of electron–phonon coupling in oxide superlattices

Strain effect on electronic transport and ferromagnetic transition temperature in La 0.9 Sr 0.1 MnO 3 thin films

Investigation of the structural, optical and magnetic properties of CuO/CuFe2O4 nanocomposites synthesized via simple microemulsion method

Magnetic pinning of flux lines in heterostructures of cuprates and manganites