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

Spin Hall effects convert charge currents into spin currents and vice versa even in nonmagnetic conductors due to spin orbit coupling. This enables spin Hall effects to be utilized both for the generation and detection of spin currents and magnetization dynamics. This paper reviews the experimental characterization of these effects in metallic systems, which have so far shown the highest efficiency in using spin Hall effects for charge-to-spin interconversion. The advantages and disadvantages of complimentary measurement techniques are discussed and in addition an outlook of the possible impact on applications is presented.

Spin Hall Effects in Metals

Twenty years ago in a series of amazing discoveries it was found that a large family of ceramic cuprate materials exhibited superconductivity at temperatures above, and in some cases well above, that of liquid nitrogen. Imaginations were energized by the thought of applications for zero-resistance conductors cooled with an inexpensive and readily available cryogen. Early optimism, however, was soon tempered by the hard realities of these new materials: brittle ceramics are not easily formed into long flexible conductors; high current levels require near-perfect crystallinity; and — the downside of high transition temperature — performance drops rapidly in a magnetic field. Despite these formidable obstacles, thousands of kilometres of high-temperature superconducting wire have now been manufactured for demonstrations of transmission cables, motors and other electrical power components. The question is whether the advantages of superconducting wire, such as efficiency and compactness, can outweigh the disadvantage: cost. The remaining task for materials scientists is to return to the fundamentals and squeeze as much performance as possible from these wonderful and difficult materials.

Materials science challenges for high-temperature superconducting wire

We investigate the influence of a well-defined reversible biaxial strain $\ensuremath{\leqslant}0.12%$ on the magnetization $(M)$ of epitaxial ferromagnetic manganite films. $M$ has been recorded depending on temperature, strain and magnetic field in $20--50\phantom{\rule{0.3em}{0ex}}\mathrm{nm}$ thick films. This is accomplished by reversibly compressing the isotropic in-plane lattice parameter of the rhombohedral piezoelectric 0.72PMN-0.28PT (001) substrates by application of an electric field $E\ensuremath{\leqslant}12\phantom{\rule{0.3em}{0ex}}\mathrm{kV}\phantom{\rule{0.2em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}1}$. The magnitude of the total variable in-plane strain has been derived. Strain-induced shifts of the ferromagnetic Curie temperature $({T}_{C})$ of up to $19\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ were found in ${\mathrm{La}}_{0.7}{\mathrm{Sr}}_{0.3}\mathrm{Mn}{\mathrm{O}}_{3}$ (LSMO) and ${\mathrm{La}}_{0.7}{\mathrm{Ca}}_{0.3}\mathrm{Mn}{\mathrm{O}}_{3}$ films and are quantitatively analyzed for LSMO within a cubic model. The effective magnetoelectric coupling coefficient $\ensuremath{\alpha}={\ensuremath{\mu}}_{0}dM∕dE\ensuremath{\leqslant}6\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}8}\phantom{\rule{0.3em}{0ex}}\mathrm{s}\phantom{\rule{0.2em}{0ex}}{\mathrm{m}}^{\ensuremath{-}1}$ at ambient temperature in the magnetic-film-ferroelectric-substrate system results from the strain-induced $M$ change. It corresponds to an enhancement of ${\ensuremath{\mu}}_{0}\ensuremath{\Delta}M\ensuremath{\leqslant}19\phantom{\rule{0.3em}{0ex}}\mathrm{mT}$ upon biaxial compression of 0.1%. The extraordinary large $\ensuremath{\alpha}$ originates from the combination of three crucial properties: (i) the strong strain dependence of $M$ in the ferromagnetic manganites, (ii) large piezo-strain of the PMN-PT substrates, and (iii) effective elastic coupling at the film-substrate interface.

Influence of strain on the magnetization and magnetoelectric effect in La 0.7 A 0.3 Mn O 3 ∕ PMN − PT ( 001 ) ( A = Sr , Ca )

The perovskite manganites with generic formula RE1?xAExMnO3 (RE = rare earth, AE = Ca, Sr, Ba and Pb) have drawn considerable attention, especially following the discovery of colossal magnetoresistance (CMR). The most fundamental property of these materials is strong correlation between structure, transport and magnetic properties. They exhibit extraordinary large magnetoresistance named CMR in the vicinity of the insulator?metal/paramagnetic?ferromagnetic transition at relatively large applied magnetic fields. However, for applied aspects, occurrence of significant CMR at low applied magnetic fields would be required. This review consists of two sections: in the first section we have extensively reviewed the salient features, e.g.?structure, phase diagram, double-exchange mechanism, Jahn?Teller effect, different types of ordering and phase separation of CMR manganites. The second is devoted to an overview of experimental results on CMR and related magnetotransport characteristics at low magnetic fields for various doped manganites having natural grain boundaries such as polycrystalline, nanocrystalline bulk and films, manganite-based composites and intrinsically layered manganites, and artificial grain boundaries such as bicrystal, step-edge and laser-patterned junctions. Some other potential magnetoresistive materials, e.g.?pyrochlores, chalcogenides, ruthenates, diluted magnetic semiconductors, magnetic tunnel junctions, nanocontacts etc, are also briefly dealt with. The review concludes with an overview of grain-boundary-induced low field magnetotransport behavior and prospects for possible applications.

https://iopscience.iop.org/article/10.1088/0953-8984/20/27/273201/pdf

Low field magnetotransport in manganites

{ital T}{sub {ital c}} and {ital dT}{sub {ital c}}/{ital dP} have been systematically measured for fully oxygenated {ital R}Ba{sub 2}Cu{sub 3}O{sub 7{minus}{delta}} ({ital R}-123) with {ital R}=Yb, Tm, Ho, Dy, Gd, Sm, and Nd. {ital T}{sub {ital c}} has been observed to increase from 88 to 94 K with increasing radius of the {ital R} ion ({ital r}) from 0.98 to 1.12 A. Based on the lattice strains and our {ital dT}{sub {ital c}}/{ital dP} data, we have calculated {ital T}{sub {ital c}} for the series of {ital R}-123 and compared them with the measured {ital T}{sub {ital c}}. Good agreement between the experimental and the calculated results strongly suggests that the {ital R} effect on {ital T}{sub {ital c}} in {ital R}-123 originates from the strain-induced charge redistribution between the charge reservoir and the CuO{sub 2} plane.

Origin of the R-ion effect on Tc in RBa2Cu3O7.

The electroresistance (ER) and magnetoresistance (MR) of ${\mathrm{La}}_{0.7}{\mathrm{Sr}}_{0.3}{\mathrm{MnO}}_{3}$ (LSMO) thin films with different thicknesses (t) are investigated. We found a metallic-to-insulating (M-I) transition in films with $t=80\mathrm{nm}.$ For the 80-nm film, a giant room-temperature ER ratio of 11.3% is achieved with an electric current of 0.9 mA. This value of the ER ratio is four times larger resistive response than that of the MR ratio under 1 T. The enhancement of the ER value in these disordered metallic LSMO thin films is correlated with the coexistence of metallic and insulating phases and attributed to the mechanism of phonon-assisted delocalization.

Current-induced giant electroresistance in La 0.7 Sr 0.3 MnO 3 thin films

Strain is one of the parameters used to control electron densities in semiconductor devices Here, the authors show that strain at the interface of two oxide thin films can lead to the condensation of the two-dimensional interfacial electron density into one-dimensional chains

/pdf/condensation-of-two-dimensional-oxide-interfacial-charges-2l5tf4kj9d.pdf

Condensation of two-dimensional oxide-interfacial charges into one-dimensional electron chains by the misfit-dislocation strain field

The effects of structural, electrical and magnetic properties with the isovalent chemical substitution of Ca2+ into the Sr2+ sites in La12(Sr18−xCax)Mn2O7 (x=0–08) are investigated The highest magnetoresistance ratio [ρ(0)/ρ(H)] of 208% (H=15 T) at a temperature of 102 K was observed for the x=04 sample The Curie temperatures decreased from 135 to 102 K for x=0–04, respectively Moreover, the Weiss constants θ were varied from the positive to negative value with increasing Ca concentration The antiferromagnetic behavior with Neel temperature around 30 K was found in the x=08 sample The magnetization measurements show that the hysteresis phenomenon appeared at the temperatures below the Curie or Neel temperatures

J. G. Lin

Papers

Origin of the R-ion effect on Tc in RBa2Cu3O7.

Current-induced giant electroresistance in La 0.7 Sr 0.3 MnO 3 thin films

Condensation of two-dimensional oxide-interfacial charges into one-dimensional electron chains by the misfit-dislocation strain field

Structural, electrical and magnetic properties of two-dimensional La1.2(Sr1.8−xCax)Mn2O7 manganites

Determination of Mn Valence from X-Ray Absorption Near Edge Structure and Study of Magnetic Behavior in Hole-Doped (Nd1−xCax)MnO3System☆