AVS2001 Session MI+EL-TuM: Spintronics I: Magnetization Dynamics and New Materials

Tuesday, October 30, 2001 8:20 AM in Room 110

Tuesday Morning

Start	Invited?	Item
8:20 AM	Invited	MI+EL-TuM-1 Noise-Derived Anisotropy Energy Distributions of Cobalt Nanoparticle Films S.I. Woods, R.H. Koch, S. Sun, J. Kirtley (IBM T.J. Watson Research Center)
9:00 AM		MI+EL-TuM-3 Spin Wave Dynamics of Interacting and Non-interacting Magnetic Elements on the Sub-micrometer Scale S.O. Demokritov, J. Jorzick, B. Hillebrands (University Kaiserslautern, Germany); M. Bailleul, C. Fermon (CEA Saclay, France); K. Guslienko, A.N. Slavin (Oakland University); D. Berkov (Innovent Jena, Germany) Confinement caused by the lateral edges of small magnetic elements qualitatively changes dynamic properties of such elements. Instead of well-known spin wave bands, characteristic for thin magnetic films that are infinite in plane, one observes quantized spin wave modes with wavevectors determined by the element lateral sizes.¹ Here we report a new highly localized spin wave mode in small magnetic elements. This mode was observed using Brillouin light scattering from thermal spin fluctuation in arrays of micrometer-size, 35 nm thick permalloy elements: rectangular dots and stripes magnetized perpendicular to their axes. The in-plane field 0.3-0.6 kOe was high enough to remove the remanence domains in the investigated elements. However, due to the non-elliptical shape of the elements the total saturation cannot be reached at any applied field. Domains (near the edges of the element that are perpendicular to the field) exist. The observed new mode is localized near those edge domains and has a frequency of 4-6 GHz depending on the applied field. The width of the localization region is much smaller than the lateral size of the element (< 200 nm). Due to high magnetic susceptibility in the region of the mode localization the mode amplitude caused by thermal fluctuation is much higher than that of the quantized modes. The experimental observation of a new mode is confirmed by a theoretical analysis, based on the solution of a non-local dipole problem, as well as by numerical simulations. If the distance between the elements in an array approaches a value comparable with their thickness, the dipole-dipole interaction between the elements becomes measurable. Due to this interaction the phase locking of the spin waves of neighboring elements takes place: spin fluctuations in different elements are correlated. Thus, a collective spin wave mode propagating through the array of magnetic elements is created. ¹J. Jorzick et al. Phys. Rev. B, 60 (1999) 15194.
9:40 AM	Invited	MI+EL-TuM-5 In-situ Characterization of Spin-dependent Scattering Mechanisms in GMR Spin Valves W.E. Bailey, S.E. Russek (NIST, Boulder) Although giant magnetoresistance (GMR) is widely used in magnetic recording, the relative importance of electronic scattering locations which contribute to--or limit--the effect is not generally agreed upon. The technologically important case of the Co/Cu/Co "spin-valve" trilayer is particularly rich since questions of surface scattering and possible channeling effects in the current-in-plane geometry (CIP-GMR) may be considered along with older questions of bulk vs. interface spin-dependent scattering. The role of surface scattering is crucial since it is widely believed that its reduction, through specularity enhancement, could provide a three-to tenfold enhancement of the spin-valve GMR. We have developed the in-situ magnetoresistance measurement as a method to locate scattering centers in the spin valve and to provide additional information on their nature. Film conductance and GMR are measured in-situ, in UHV, and in real time during magnetron sputtering, allowing the effects of interfaces and surfaces on scattering to be identified as they are created. Results from two sets of experiments will be presented. First, the onset of GMR has been investigated in NiO/Co(30)/Cu(30 Å)/Co(t) spin valves with ultrathin free layers. A main contribution to GMR is attributable to the interface alone, with a conductance response suggestive of the formation of a channeling state. Second, the response of GMR to surface treatment has been measured during coverage of NiO/Co(30)/Cu(30 Å)/Co(t) spin valves with noble metals and nano-oxide layers ("NOL"). The results in these cases do not match well with simple models of surface diffuse scattering or its reduction, and may be incompatible with them.
10:20 AM	Invited	MI+EL-TuM-7 Highly Spin-Polarized Materials C.L. Chien (Johns Hopkins University) Magnetic heterostructures of highly spin polarized materials provide opportunities for the exploration of new physical phenomena and the development of spintronic devices where both charge and spin of electrons are exploited. Materials with spin polarizat ion (P) higher than those of traditional ferromagnets (P < 45% for Fe, Co, and Ni), and especially half-metallic ferromagnets with P = 100%, are highly desirable. We describe the measurements of the intrinsic spin polarization of half-metallic CrO2 with P = 96% and the unique magnetic and other electronic properties of these single-crystal CrO2 films, epitaxially grown on TiO2 substrates by chemical vapor deposition.
11:00 AM		MI+EL-TuM-9 Characterization of a New Half-Metallic Ferromagnet: Yb₁₄MnSb₁₁ A.P. Holm, S.M. Kauzlarich (University of California, Davis); S.A. Morton, G.D. Waddill (University of Missouri-Rolla); W.E. Pickett (University of California, Davis); J.G. Tobin (Lawrence Livermore National Laboratory) Utilizing a combination of bulk magnetization and magnetic X-ray circular dichroism measurements (MXCD), we demonstrate that Yb₁₄MnSb₁₁ is a half-metallic ferromagnet. The compound is isostructural to Ca₁₄AlSb₁₁, with the Mn occupying the Al site in the [AlSb₄]^9- discrete tetrahedral, anionic unit. Bulk magnetization measurements exhibit an effective moment of 4.86 ± 0.02 µ_B/ formula unit implying a Mn³⁺, high spin d⁴ state, but theoretical calculations suggest Mn is divalent with one hole in the Sb 5p states of the tetrahedron. MXCD measurements reveal that the Mn L₂₃ is strongly dichroic, and there is no evidence of any dichroism in either the Yb N₄₅ or Sb M₄₅ edges. Comparisons of the Mn spectra with the theoretical models for Mn²⁺ show excellent agreement, and support the bulk magnetization measurements. The bulk magnetization measurements clearly show full spin alignment and the cancellation of one spin by the unpaired and antialigned spin in the Sb 5p band.