Why evaporated permalloy/Cu multilayers do not exhibit GMR effect: In-situ transport properties

Lucinski T, Reiss G, Mattern N, Rank R. Why evaporated permalloy/Cu multilayers do not exhibit GMR effect: In-situ transport properties. TRENDS AND NEW APPLICATIONS OF THIN FILMS. 1998;287-2:449-454.Thermally evaporated permalloy/copper (Py/Cu) multilayers were deposited onto quarts glass substrate, oxidised and etched Si wafers at room temperature and at 100 K. The samples were examined during an evaporation process by means of in-situ conductance measurements whereas magnetisation, A-my diffraction, atomic force microscopy and the cross section electron transmission microscopy were performed exsitu to characterise our samples. Only very small GMR effect was observed for samples deposited at R.T. and at 100 K. An absence of the antiferromagnetic coupling seems to result from the large interface roughness. Multilayers deposited at 100 A showed the existence of highly topological disordered alloy-like structure formed during deposition process. Introduction In contrast to sputtered (Ni80Fe20=Py)/Cu multilayers (MIs) [1,2] no GMR oscillatory behaviour has been noticed for evaporated samples as a function of Cu sublayer thickness [3]. The GMR effect for evaporated Py/Cu Mis was only observed in a post annealing state [3] whereas annealing of the sputtered Py/Cu Mis even at low temperatures can led to gradual degradation of the Interlayer coupling as well as of the GMR effect [2]. This strongly indicates the influence of the deposition technique on the interlayer coupling and on the chin effect in Py/Cu multilayers. In this contribution we present reasons why far evaporated Py/Cu multilayers no GMR effect is observed. We compare the morphology, surface topography and crystal structure of Py/Cu Mis deposited by evaporation at room temperature (R.T.) and at 100 K. Experimental The [Ni80Fe20/Cu](N) (N denotes a number of bilayers and N less than or equal to 30) Mts were evaporated in UHV system from Al2O3 crucibles onto different substrates (etched Si, oxidised Si wafers and a quarts glass) covered with Py or Cu buffer layers or without any buffer layer. Thickness of evaporated layers were controlled by a quartz micro-balance. The residual pressure in the vacuum chamber with liquid nitrogen baffle was 0.06 mPa. The deposition rate for both Py and Cu evaporated materials was about 0.01 nm/sec and the distance between crucibles and substrate holder was 50 cm. Thicknesses of Py (d(Py)) and Cu (d(Cu)) sublayers were changed in the range of 0.8 less than or equal to d(Py)(d(Cu))less than or equal to 2.5 nm. The surface topography and the crystal structure of the samples were examined ex-situ by atomic force microscopy (AFM), low-(LAXRD) and high angle X-ray diffraction (HAXRD) using Cu K-alpha radiation. The morphology of selected samples has been examined by means of the transmission electron microscopy of cross-section (TEM-CS). Conductance of the samples and their magnetoresistance were measured insitu during the deposition process with a pseudo-four point method. The magnetic properties of selected samples have been measured ex-situ at room temperature with a vibrating sample magnetometer (VSM) in-plane (i-p) and out-of-plane (o-p). Results and Discussion

Excitation energy transfer and charge separation are affected in Arabidopsis thaliana mutants lacking light-harvesting chlorophyll a/b binding protein Lhcb3

The composition of LHCII trimers as well as excitation energy transfer and charge separation in grana cores of Arabidopsis thaliana mutant lacking chlorophyll a/b binding protein Lhcb3 have been investigated and compared to those in wild-type plants. In grana cores of lhcb3 plants we observed increased amounts of Lhcb1 and Lhcb2 apoproteins per PSII core. The additional copies of Lhcb1 and Lhcb2 are expected to substitute for Lhcb3 in LHCII trimers M as well as in the LHCII "extra" pool, which was found to be modestly enlarged as a result of the absence of Lhcb3. Time-resolved fluorescence measurements reveal a deceleration of the fast phase of excitation dynamics in grana cores of the mutant by ∼ 15 ps, whereas the average fluorescence lifetime is not significantly altered. Monte Carlo modeling predicts a slowing down of the mean hopping time and an increased stabilization of the primary charge separation in the mutant. Thus our data imply that absence of apoprotein Lhcb3 results in detectable differences in excitation energy transfer and charge separation

Presence and absence of antiferromagnetic coupling and giant magnetoresistance in sputtered and evaporated permalloy/copper multilayers

Reiss G, van Loyen L, Lucinski T, et al. Presence and absence of antiferromagnetic coupling and giant magnetoresistance in sputtered and evaporated permalloy/copper multilayers. JOURNAL OF MAGNETISM AND MAGNETIC MATERIALS. 1998;184(3):281-288.In multilayered thin films consisting of permalloy (Ni80Fe20) and copper, a strong antiferromagnetic coupling and a related giant magnetoresistance can be found which oscillates with the thickness of the copper spacer layers. This, however, is usually detected only in sputtered films, whereas evaporated multilayers often show no or only a very weak coupling and giant magnetoresistance. Here, we report on a comparative study of sputtered and evaporated multilayers. In the first maximum of the antiferromagnetic coupling, i.e. at a copper thickness of 0.9 nm, our sputtered films exhibit a saturation field of up to 1000 Oe and values of the giant magnetoresistance of up to 22% at room temperature at a permalloy thickness of about 2 nm. In contrast to this, the corresponding evaporated multilayers do not show any sign of antiferromagnetic coupling. A subsequent analysis of the films by cross-sectional transmission electron microscopy imaging indicates, in small regions, a good and a poor multilayered structure for sputtered and evaporated films, respectively. X-ray reflectivity measurements and atomic force imaging of the surfaces pointed to an increased interface roughness in the evaporated films. Thus we conclude that the absence of the antiferromagnetic coupling in the evaporated films should be related to an increased roughness of the layer interface and not to interdiffusion. (C) 1998 Elsevier Science B.V. All rights reserved