Thesis (Ph. D.)--Florida State University, 2003. / Advisor: Dr. Peng Xiong, Florida State University, College of Arts and Sciences, Dept. of Physics. Title and description from dissertation home page (viewed Apr. 9, 2004). Includes bibliographical references.

A metal-to-insulating transition has been observed in iron, iron oxide, iron silicide and cobalt silicide thin films when deposited on Si substrate with a native SiOx layer. This transition produced a change in resistance of 5 orders of magnitude at a temperature of 250 K. To the best of the author's knowledge, this effect has not been reported in the literature prior to this study. This work reports a systematic experimental investigation carried out to understand the fundamental mechanism involved in the manifestation of this metal-to-insulator transition. The films were deposited using the pulsed laser deposition technique (PLD) in a base vacuum of the order of 10-6 torr at 400o C and room temperature. Several experiments were systematically conducted to understand the nature of the transition and the current path. Deposition of films on different substrates and the deposition of different transition metal films were made to narrow down the physical origin of the transition in the sample. Temperature-dependent resistance measurements not only exhibited a transition but also suggested more than one conduction mechanism. This is confirmed by the data collected for the IV curves. Current and voltage have a linear relation at temperatures greater than the transition temperature, and a non-linear relation at lower temperatures. Magnetoresistance (MR) measurements revealed a quadratic dependence of the resistance on the applied magnetic field. This is an indication that the MR observed is due to Lorentz forces acting on the charge carriers. Transmission electron microscopy and x-ray photoelectron spectroscopy have identified different layers that are believed to be responsible for the observed transition.

The manufacturing of nanocontact-based spin-torque oscillators (NC-STOs)has opened the door for spintronic devices to play a part as active microwaveelements. The NC-STO has the capability of converting a direct current intoa microwave signal, and vice versa, by utilizing the spin transfer torque (STT)in ferromagnetic multilayer systems. However, the high-frequency operation ofNC-STOs typically requires high magnetic fields and the microwave power theygenerate is rather limited. As a result, NC-STOs are not yet commercially used,and they require improvements in both material systems and device geometriesbefore they can find actual use in microwave applications. In order to improve and advance this technology, NC-STOs are requiredwith both different nanocontact (NC) sizes and geometries, and using differ- ent stacks of magnetic materials. This dissertation presents experimental in- vestigations into the manufacturing of such devices using different fabrication techniques and a number of different magnetic material stacks. Currently, the fabrication of NC-STOs is limited to advanced laboratories, because NC fabri- cation requires high-resolution lithography tools. In the present work, we have developed an alternative method of fabrication, which does not require such tools and has the capability of fabricating NC-STOs having one to hundreds of NCs in a variety of sizes, possibly  down to 20 nm. Devices fabricated with this method have shown mutual synchronization of three parallel-connected NCs, and pairwise synchronization in devices with four and five NCs. Furthermore, the present work demonstrates low-field operation (down to0.02 Tesla) of NC-STOs at a record high frequency of 12 GHz. This wasachieved by implementing multilayers with a perpendicular magnetic anisotropy(PMA) material in the free layer of the NC-STO. In addition, the fabricateddevices revealed an unexpected dynamic regime under large external appliedfield (above 0.4 Tesla). The new dynamic regime was found to be due to anentirely novel nanomagnetic dynamic object â a so-called magnetic droplet soliton,predicted theoretically in 1977 but not experimentally observed until now.Detailed experiments and micromagnetic simulations show that the droplet hasvery rich dynamics. Finally,  spin-torque-induced  transverse spin wave instabilities have beenstudied.  A NC-STO with  a material stack consisting of a single ferromag- netic metal sandwiched between two non-ferromagnetic metals was fabricated. Prior to this work, evidence of spin wave instabilities was reported as resis- tance switching in nanopillar- and mechanical point contact based STOs. In the present  work, the fabricated NC-STOs showed actual microwave  signals up to 3 GHz under zero applied field with strong current hysteresis. All  the fabricated NC-STOs open up new means of studying STT in different environ- ments, in order to resolve their current drawbacks for industrial applications. / <p>QC 20130527</p>

在磁性材料中的電阻率會隨著磁場與電流的夾角不同而改變且磁場平行於電流時會大於磁場垂直於電流時的值(ρH‖I > ρH⊥I)，此現象稱作異向性磁阻(Anisotropic Magnetoresistance, AMR)效應。而在薄膜材料中，因為和塊材的形狀差異，磁場垂直於電流的電阻率又可以分為磁場方向平行於膜面(ρ⊥HIP)和磁場方向垂直於膜面 (ρ⊥HPP)。而依這兩者在單層膜與多層膜中不一樣的行為又可以分作兩種效應。在Co、Ni的單層膜中ρ⊥HIP > ρ⊥HPP，此現象稱為幾何尺寸效應(Geometric Size Effect, GSE)，而在Co/Pt的多層膜中ρ⊥HPP > ρ⊥HIP，與幾何尺寸效應果相反，此現象稱為異向性界面磁阻(Anisotropic Interface Magnetoresistance, AIMR)。而我們在Pd/Ni、Cu/Ni多層膜中更是看到磁場方向垂直於膜面 (ρ⊥HPP)大於磁場平行於電流(ρH‖I)，這是和異向性磁阻(Anisotropic Magnetoresistance, AMR)效應完全相反的現象，我們稱作反常異向性磁阻(Inverse AMR)效應 本實驗製作的樣品皆為磁性層與非磁性層交錯的多層膜，磁性層材料為鎳(Ni)，非磁性層的材料則選用接近滿足Stoner 準則(Stoner criterion)之一的鈀(Pd)，以及遠離此準則且自旋軌道交互作用很弱的銅(Cu)當對照組。而為了釐清其發生機制，所以分別做了兩種類型的樣品，第一類是固定單層膜厚改變層數，第二類是固定層數及磁性層(非磁性層)改變非磁性層(磁性層)。完成後的樣品首先以XRD確認樣品的膜厚與品質，接著在10 K和300 K的溫度量測電阻與角度的關係及磁場平行(LMR)、垂直(PMR)於電流時的磁阻，在10K時，以Pd/Ni為材料的多層膜中有看到反常異向性磁阻(Inverse AMR)效應，在300K時，以Cu/Ni為材料的第一類樣品有看到此效應，之後我們還有在不同溫度下量測電阻與角度的關係並找到其效應轉變的溫度。 由實驗結果推論，不同材料中觀察到的結果，物理機制並不相同；應該與介面性質有關。但是物理理論上的解釋還需要更進一步地探討。

Thesis (M.S.)--State University of New York at Binghamton, Department of Physics, 2006. / Includes bibliographical references.

Thesis (Ph. D.)--University of Washington, 2007. / Vita. Includes bibliographical references (leaves 122-125).

Thesis (Ph. D.)--University of Missouri-Columbia, 1997. / Typescript. Vita. Includes bibliographical references. Also available on the Internet.

Thesis (Ph. D.)--University of Missouri-Columbia, 1997. / Typescript. Vita. Includes bibliographical references. Also available on the Internet.

Thesis (Ph. D.)--University of California, San Diego, 2000. / Vita. Includes bibliographical references.

Thesis (Ph. D.)--University of Texas at Austin, 2007. / Vita. Includes bibliographical references.