ACM

com Pam Malagò Dipartimento di Fisica e Geologia P. O. Box 6221 Italy malago@affiliation. org Steve Fin Dipartimento di Fisica e Scienze P. O. org Mike Madami Dipartimento di Fisica e Geologia P. O. Box 6221 Italy madami@affiliation. org Glen Carlotti Dipartimento di Fisica e Geologia P. O. Madami, and G. Carlotti. SIG Proceedings Paper in word Format. In Proceedings of ACM Woodstock conference, El Paso, Texas USA, July 1997 (WOODSTOCK’97), 4 pages. org/10.  EXPERIMENTAL AND COMPUTATIONAL DETAILS 2.  Sample Fabrication Py/Co bi-component structures consisting of closely spaced (gap size d  35 nm) elliptical dots of thickness 25 nm, length 1 m and width 225 nm, respectively, dispersed in two different kinds of lattices, were fabricated by a self-aligned shadow deposition technique [6–8]. The Py composition is Ni80Fe20. The array is organized into closely-packed chains with inter-dot distance along the chain of D  140 nm while the inter-chain distance is D  600 nm.

The scanning electron microscopy image of the investigated bi-component sample, shown as inset of Fig. To complement the above analysis of the magnetization evolution under an external field, the magnetic states of the bi-component structures were directly imaged at different point of the hysteresis cycle using in-field magnetic force microscopy (MFM) [5]. Eavesdropping.  MFM images were recorded by a Digital Instruments Nanoscope IIIa, using the phase detection mode, i. e. monitoring the cantilever's phase of oscillation while the magnetic tip was scanning the sample surface at a distance of 120 nm on the average (lift mode). To reproduce the exact shape of the dots, a bitmap image of the basic unit of the bi-component dots was created from the SEM image of Fig. and used as input for the simulations. Periodic boundary conditions have been applied to account for the chain arrangement of the Py/Co dots in the investigated sample.

 Micromagnetic.  For each micromagnetic cell the reduced magnetization takes the form where the magnetization (saturation magnetization) in the k-th cell; note that the saturation magnetization now depends on the ferromagnetic material through the index k. At point  (H  372 Oe) of the hysteresis loop, where the plateau is observed in the M-H loop, the dark and bright spots of the Py dots are reversed with respect to those of Co, accounting for an antiparallel relative alignment of magnetization.  RESULTS AND DISCUSSION 3.  Magnetization Curves and MFM Characterization The major hysteresis loop measured by MOKE, plotted in Fig. displays a two-step switching process due to the distinct magnetization reversal of the Py and Co sub-elements, characterized by a different coercivity. As the field is reduced from positive saturation (upper branch of the M-H loop), a 100% remanence is attained.

remanent state coming from negative saturation, as confirmed by the MFM image taken at point  of Fig. We have also used MFM to measure the magnetic configurations along the minor hysteresis loop, described above. Once the AP ground state has been generated at H  500 Oe, the applied field is increased in the positive direction. The MFM image taken at point ' of Fig. remanent state of the minor loop (H  0), shows that the AP state is stable and remains unchanged until the magnetic field is increased up to 300 Oe where the Py magnetization reverses its orientation and returns to be aligned with that of Co dots. They exhibit marked localization into either the Co or the Py dots, as stated at the end of the previous Section, were it was introduced the labelling notation containing the dominant localization region (either Py or Co) and the spatial symmetry (EM, F, DE, etc).

When the dots are in the P state, up to five modes were detected in BLS spectra. On the basis of the calculated profiles (right panel of Fig. we identified in the P state the two modes at lowest frequencies as the EM(Py) and the F(Py), with a very small spin precession amplitude into the Co dot. This is because for this material we are below the frequency threshold for the existence of spin waves. Notice that if one stops increasing the negative field to about 300 Oe and comes back towards positive applied fields, BLS measurements can be performed following the minor hysteresis loop. This method permits to study, for example, the magnetization dynamics at remanence (without any external applied magnetic field) when the system is in the AP state (see MFM image ' in Fig.

a configuration which cannot be achieved at remanence along the major M-H loop. In Fig. we show the modes frequency measured along the minor loop (full points) and compare them with values measured along the major M-H loop (open points). GHz and 0. GHz, respectively, while that of F(Py) decreases by 0. GHz. The reason of this complex behavior will be addressed in the following, analyzing the interplay of both static and dynamic dipolar coupling between the adjacent Py and Co dots Table 2. This is a clear indication that both the Py and Co sub-elements are in a single domain state where Py and Co magnetizations are all oriented with their magnetic moment along the chain and field direction. Several eigenmodes have been identified and their frequency evolution as a function of the intensity of the applied magnetic field has been measured by Brillouin light scattering technique, encompassing the ground states where the cobalt and permalloy dots magnetizations are parallel or anti-parallel, respectively.

In correspondence to the transition between the two different ground states, the mode frequency undergoes an abrupt variation and more than that, in the anti-parallelstate, the frequency is insensitive to the applied field strength. The experimental results have been successfully interpreted by the dynamic matrix method which permits to calculate both the mode frequencies and the spatial profiles. A HEADINGS IN APPENDICES The rules about hierarchical headings discussed above for the body of the article are di. erent in the appendices. A.  Dynamic Measurements: BLS A.  Ground-State Magnetization Determination and DMM Micromagnetic Simulations Determined. Micromagnetic A.  Results and Discussion A. DOI: http://dx. doi. org/10. I. F. Master’s thesis. Royal Institute of Technology (KTH), Stockholm, Sweden. P. Bahl, R. Chancre, and J. Dissertation. Stanford University, Palo Alto, CA. UMI Order Number: AAT 8506171.

Jacques Cohen (Ed. Special Issue: Digital Libraries. doi. org/10. Ian Editor (Ed. The title of book two (2nd. ed.