Magnetic anisotropy and magnetodielectric coefficients in Cr 2O3 and Fe0.4Cr1.6O3

The temperature dependence of magnetization, magnetic anisotropy, coercive field and the magnetodielectric coefficient of Cr2O3 (undoped) and Fe0.4Cr1.6O3 (doped) was experimentally investigated. Test data shows that the presence of Fe ions at the interstitial spaces of the Cr2O3 crystal lattice decreases the Neel Temperature by ∼80 K when compared to the undoped Cr 2O3. Also both the doped and undoped samples display maxima in magnetic anisotropy and magnetodielectric coefficient as a function of temperature. The maxima for the Fe doped samples occurs at a temperature approximately 80 K below the temperature measured for the Cr2O 3 samples, i.e. similar to the shift observed in the Neel Temperature. These results suggest that Neel Temperature, magnetic anisotropy, and the magnetodielectric coefficients are physically interrelated through competing principal exchange interactions and may provide a useful approach to search for new multiferroic materials. © 2014 Elsevier B.V. All rights reserved

Fabrication and characterization of functionally graded Ni-Ti multilayer thin films

A functionally graded multilayer Ni–Ti thin film was deposited on a SiO₂/Si substrate by d.c. sputtering using a ramped heated Ni–Ti alloy target. The stand-alone films were crystallized at 500°C in vacuum better than 10¯⁷ Torr. Transmission electron microscopy micrographs taken along the film cross section show two distinct regions, thin and thick, with weak R and B2 phases, respectively. The film compositions along the thickness were measured and quantified using the standard-less EELSMODEL method. The film deposited during the initial thermal ramp (thin regions) displays an average of 54 at.% Ni while the film deposited at a more elevated target temperature (thick regions) shows about 51 at.% Ni.status: publishe

Enhanced magnetoelectric coupling in a composite multiferroic system via interposing a thin film polymer

Enhancing the magnetoelectric coupling in a strain-mediated multiferroic composite structure plays a vital role in controlling magnetism by electric fields. An enhancement of magnetoelastic coupling between ferroelectric single crystal (011)-cut [Pb(Mg1/3Nb2/3)O3](1-x)-[PbTiO3]x (PMN-PT, x≈ 0.30) and ferromagnetic polycrystalline Ni thin film through an interposed benzocyclobutene polymer thin film is reported. A nearly twofold increase in sensitivity of remanent magnetization in the Ni thin film to an applied electric field is observed. This observation suggests a viable method of improving the magnetoelectric response in these composite multiferroic systems

Enhanced magnetoelectric coupling in a composite multiferroic system via interposing a thin film polymer

Enhancing the magnetoelectric coupling in a strain-mediated multiferroic composite structure plays a vital role in controlling magnetism by electric fields. An enhancement of magnetoelastic coupling between ferroelectric single crystal (011)-cut [Pb(Mg1/3Nb2/3)O3](1-x)-[PbTiO3]x (PMN-PT, x≈ 0.30) and ferromagnetic polycrystalline Ni thin film through an interposed benzocyclobutene polymer thin film is reported. A nearly twofold increase in sensitivity of remanent magnetization in the Ni thin film to an applied electric field is observed. This observation suggests a viable method of improving the magnetoelectric response in these composite multiferroic systems

Tunable Magnetoelastic Effects in Voltage-Controlled Exchange-Coupled Composite Multiferroic Microstructures.

The magnetoelectric properties of exchange-coupled Ni/CoFeB-based composite multiferroic microstructures are investigated. The strength and sign of the magnetoelastic effect are found to be strongly correlated with the ratio between the thicknesses of two magnetostrictive materials. In cases where the thickness ratio deviates significantly from one, the magnetoelastic behavior of the multiferroic microstructures is dominated by the thicker layer, which contributes more strongly to the observed magnetoelastic effect. More symmetric structures with a thickness ratio equal to one show an emergent interfacial behavior which cannot be accounted for simply by summing up the magnetoelastic effects occurring in the two constituent layers. This aspect is clearly visible in the case of ultrathin bilayers, where the exchange coupling drastically affects the magnetic behavior of the Ni layer, making the Ni/CoFeB bilayer a promising next-generation synthetic magnetic system entirely. This study demonstrates the richness and high tunability of composite multiferroic systems based on coupled magnetic bilayers compared to their single magnetic layer counterparts. Furthermore, because of the compatibility of CoFeB with present magnetic tunnel junction-based spintronic technologies, the reported findings are expected to be of great interest for the development of ultralow-power magnetoelectric memory devices

Functional Fatigue and Tension–Compression Asymmetry in [001]-Oriented Co49Ni21Ga30 High-Temperature Shape Memory Alloy Single Crystals

Conventional shape memory alloys cannot be employed for applications in the elevated temperature regime due to rapid functional degradation. Co–Ni–Ga has shown the potential to be used up to temperatures of about 400 °C due to a fully reversible superelastic stress–strain response. However, available results only highlight the superelastic response for single cycle tests. So far, no data addressing cyclic loading and functional fatigue are available. In order to close this gap, the current study reports on the cyclic degradation behavior and tension–compression asymmetry in [001]-oriented Co49Ni21Ga30 single crystals at elevated temperatures. The cyclic stress-strain response of the material under displacement controlled superelastic loading conditions was found to be dictated by the number of active martensite variants and different resulting stabilization effects. Co–Ni–Ga shows a large superelastic temperature window of about 400 °C under tension and compression, but a linear Clausius–Clapeyron relationship could only be observed up to a temperature of 200 °C. In the present experiments, the samples were subjected to 1000 cycles at different temperatures. Degradation mechanisms were characterized by neutron diffraction and transmission electron microscopy. The results in this study confirm the potential of these alloys for damping applications at elevated temperatures