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Multiferroic nanocomposites, consisting of branched, ferrimagnetic CoFe2O4 filaments and large protruding PbTiO3 particles embedded in a piezoelectric PbTiO3 matrix, have been fabricated by co-deposition using metalorganic chemical vapor deposition. Branched CoFe2O4 filaments reduce the CoFe2O4/PbTiO3 interfacial strain and induce a perpendicular magnetic anisotropy. Three-dimensional characterizations reveal that in addition to the c-domain, grains with a second orientation in PbTiO3 particles contribute to an additional four apparent variants of polarization. In contrast, the PbTiO3 matrix exhibits only c-domain polarization with a smaller magnitude. The smaller piezoresponse results from the constraints imposed by the branched CoFe2O4 filaments. Three-dimensional microstructure and property analysis provide a comprehensive insight on the structure-property relationship of multiferroic nanocomposites grown by metalorganic chemical vapor deposition.

Three-dimensional atom-probe tomography and transmission electron microscopy have been utilized to study the effects of Ta getter presputtering and either a Mg or Ru free-layer cap on the elemental distributions and properties of MgO-based magnetic tunnel junctions after annealing. Annealing the samples resulted in crystallization of the amorphous CoFeB layer and diffusion of the majority of the boron away from the crystallized CoFeB layers. The Ta getter presputter is found to reduce the segregation of boron at the MgO/CoFeB interface after annealing, improving the tunneling magnetoresistance of the tunnel junction. This effect is observed for samples with either a Ru free-layer cap or a Mg free-layer cap and is thought to be a result of a reduced oxygen concentration within the MgO due to the effect of Ta getter presputtering. A Ru free-layer cap provides superior magnetic and magnetotransport properties compared to a Mg free-layer cap. Mg from the Mg free-layer cap is observed to diffuse toward the MgO...

The effect of the crystallinity and the grain texturing of CoPt hard layers on exchange coupled Fe/CoPt soft/hard magnetic systems was studied using gradient thickness multilayer thin films. We have studied the hard layer structures by transmission electron microscopy and x-ray diffraction, and characterized the exchange coupling interaction through magnetization loops obtained by the magneto-optical Kerr effect measurement. We found that exchange coupling strongly depends on the crystalline characteristics of the CoPt hard layer. There is correlation between the mixture of different grain orientations of the CoPt hard layer and coupling efficiency. In particular, interlayer coupling is enhanced when there is only one orientation, namely, the L10 CoPt structure with its c-axis inclined at 45° with respect to the substrate plane. An increased degree of mixture of the latter with the in-plane-c-axis L10 CoPt structure is detrimental to obtaining one-phase-like magnetization loops. The present work points to...

The experiments on the [t1Pt/0.4Co]5/(0.2–5.0)Ru/[0.4Co/t2Pt]5 (thickness unit is nm) multilayers with perpendicular anisotropy (PA) indicate that the interlayer coupling shows an antiferromagnetic (AF) and a ferromagnetic oscillatory behavior with the thickness of Ru spacer layers from 0 to 5.0 nm, and that the AF oscillations display a superposition of two different periods, which are 0.8 and 1.1 nm, respectively. Moreover, we found that the magnitude of AF coupling strength J is closely related to the magnitude of PA caused by varied thickness of nonmagnetic Pt layer. Our experimental results can be explained by Bruno’s electron-optics model.

Department of Physics, University of Texas at Arlington. Ames Laboratory and Department of Materials Science and Engineering, Iowa State University. NanoTech Institute, University of Texas at Dallas.

Magnetotransport measurements were performed on n-type conducting Co-doped ZnO and Mn-doped ZnO films prepared by pulsed laser deposition on a-plane sapphire substrates, and positive magnetoresistance (MR) was observed at low temperature. The positive MR decreases drastically with the free electron concentration n exceeding 1019cm−3 and reveals almost the same dependency on n for Co-doped ZnO and Mn-doped ZnO. This hints towards a similar s-d exchange constant in both types of magnetic ZnO films. For Co-doped ZnO, the saturated anomalous Hall resistivity increases with decreasing electron concentration. No anomalous Hall effect was observed in Mn-doped ZnO. Within a free electron approximation the positive MR may be related with the spin polarization of conducting electrons due to s-d exchange interactions. The modeled spin splitting of the conduction band is smaller than 10meV.

The antiferromagnetic L10 CrPt film synthesized through annealing equiatomic [Pt∕Cr] multilayer stack can pin the adjacent Co0.9Fe0.1 film with medium exchange anisotropy and high stability. It has been found that when an ultrathin Mn layer is inserted between the Co0.9Fe0.1 film and the [Pt∕Cr] multilayer, the exchange anisotropy of the CoFe∕CrPt film is enlarged fourfold, reaching 0.48erg∕cm2 at room temperature, which is comparable to the best room-temperature result ever achieved in all practical biasing materials except the ordered IrMn3. Nevertheless, the interfacial Mn addition does not lower the high blocking temperature of CoFe∕CrPt films with its remaining value of 600°C. The structural characterization reveals that the added Mn atoms still distribute around the interface when the [Pt∕Cr] multilayer is transformed into ordered CrPt film after annealing. It seems that the Mn atoms are preferably combined with the neighboring Pt∕Cr layers during the annealing to form a modified interfacial antifer...