The manganese oxides of general formula RE1−xMxMnO3 (RE = rare earth, M = Ca, Sr, Ba, Pb) have remarkable interrelated structural, magnetic and transport properties induced by the mixed valence (3+–4+) of the Mn ions. In particular, they exhibit very large negative magnetoresistance, called colossal magnetoresistance (CMR), in the vicinity of metal–insulator transition for certain compositions. In this review paper, we summarize the most important features of the physics of the CMR manganites. The growth techniques for manganese oxide thin films, which are the basic material for potential applications, are reviewed and their structure and morphology examined in relation to growth parameters. The effects of epitaxial strains on the physical properties are discussed. Early works on superlattices and devices are presented.

http://iopscience.iop.org/article/10.1088/0022-3727/36/8/201/pdf

CMR manganites: physics, thin films and devices

Magnetic oxides show a variety of extrinsic magnetotransport phenomena: grain-boundary, tunnelling and domain-wall magnetoresistance. In view of these phenomena the role of some magnetic oxides is outstanding: these are believed to be half-metallic having only one spin-subband at the Fermi level. These fully spin-polarized oxides have great potential for applications in spin-electronic devices and have, accordingly, attracted intense research activity in recent years. This review is focused on extrinsic magnetotransport effects in ferromagnetic oxides. It consists of two parts; the second part is devoted to an overview of experimental data and theoretical models for extrinsic magnetotransport phenomena. Here a critical discussion of domain-wall scattering is given. Results on surface and interfacial magnetism in oxides are presented. Spin-polarized tunnelling in ferromagnetic junctions is reviewed and grain-boundary magnetoresistance is interpreted within a model of spin-polarized tunnelling through natural oxide barriers. The situation in ferromagnetic oxides is compared with data and models for conventional ferromagnets. The first part of the review summarizes basic material properties, especially data on the spin polarization and evidence for half-metallicity. Furthermore, intrinsic conduction mechanisms are discussed. An outlook on the further development of oxide spin-electronics concludes this review.

Extrinsic magnetotransport phenomena in ferromagnetic oxides

We review the recent developments in the electric field control of magnetism in multiferroic heterostructures, which consist of heterogeneous materials systems where a magnetoelectric coupling is engineered between magnetic and ferroelectric components. The magnetoelectric coupling in these composite systems is interfacial in origin, and can arise from elastic strain, charge, and exchange bias interactions, with different characteristic responses and functionalities. Moreover, charge transport phenomena in multiferroic heterostructures, where both magnetic and ferroelectric order parameters are used to control charge transport, suggest new possibilities to control the conduction paths of the electron spin, with potential for device applications.

https://iopscience.iop.org/article/10.1088/0953-8984/24/33/333201/pdf

Electric field control of magnetism in multiferroic heterostructures

The drive to develop materials with new multifunctional capabilities has rekindled interest in multiferroics—systems which are characterized by the simultaneous presence of, and coupling between, magnetic and electric order parameters. In naturally occurring multiferroics the magnetoelectric coupling is often weak, and new classes of artificially structured composite materials that combine dissimilar magnetic and ferroelectric systems are being developed to optimize order parameter coupling. [1–6] Here, we describe direct, charge-mediated magnetoelectric coupling in a heterogeneous multiferroic that takes advantage of the sensitivity of a strongly correlated magnetic system to competing electronic ground states. Using magneto-optic Kerr effect magnetometry, we observe large magnetoelectric coupling in ferroelectric/lanthanum manganite heterostructures, including electric field-controlled on/off switching of magnetism. These results open a new vista for the development of novel magnetoelectric devices with large charge coupling between electric and magnetic degrees of freedom. Doped lanthanum manganites are complex oxides characterized by a strong interplay between electron transport, magnetism, and crystal lattice distortions, leading to a rich variety of electronic behavior, including magnetic and charge-ordered states, colossal magnetoresistance (CMR), and a diversity of electron transport behavior. Underlying the competition between these ground states is the prominent role of charge in double exchange, hopping, and orbital overlap. [7,8] To date, controlling charge as a parameter has most often been achieved using chemical doping, which is robust, and permanent. An alternative approach to

Magnetoelectric Effects in Complex Oxides with Competing Ground States

Concomitant with the development of metal-based spintronics in the late 1980s and 1990s, important advances were made on the growth of high-quality oxide thin films and heterostructures. While this was at first motivated by the discovery of high-temperature superconductivity in perovskite Cu oxides, this technological breakthrough was soon applied to other transition-metal oxides and, notably, mixed-valence manganites. The discovery of colossal magnetoresistance in manganite films triggered intense research activity on these materials, but the first notable impact of magnetic oxides in the field of spintronics was the use of such manganites as electrodes in magnetic tunnel junctions, yielding tunnel magnetoresistance ratios that are one order of magnitude larger than what had been obtained with transition-metal electrodes. Since then, research on oxide spintronics has been intense, with the latest developments focused on diluted magnetic oxides and, more recently, on multiferroics. In this paper, the most important results on oxide spintronics was reviewed, emphasizing materials physics as well as spin-dependent transport phenomena, and finally give some perspectives on how the flurry of new magnetic oxides could be useful for next-generation spintronics devices

Oxide Spintronics

To understand the near-interface magnetism in manganites, ultrathin films of La0.67Sr0.33MnO3 were grown epitaxially on single-crystal (001) LaAlO3 and (110) NdGaO3 substrates. The temperature and magnetic field-dependent film resistance is used to probe the film’s structural and magnetic properties. A surface and/or interface related dead layer is inferred from the thickness-dependent resistance and magnetoresistance. The total thickness of the dead layer is estimated to be ∼30 A for films on NdGaO3 and ∼50 A for films on LaAlO3.

D. W. Abraham

Papers

Thickness-dependent magnetotransport in ultrathin manganite films