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The swelling-activated chloride current, commonly referred to as ICl,swell, is an outwardly-rectifying anion current that plays an important role in cell volume regulation, among other capacities. Despite several decades of research, the molecular identity of the channel responsible for this chloride current remains controversial. Recent indications that key endogenous sulfhydryl groups are capable of modifying the current led us to assess the effects of several divalent cations, including zinc, on ICl,swell. Zinc is known to tightly associate with sulfhydryl groups such as in zinc finger proteins. We found that extracellular zinc irreversibly inhibited ICl,swell at a site downstream in the signaling cascade. Moreover, zinc blocking kinetics were voltage dependent, suggesting interaction with a site within the electric field, across the pore of the channel responsible for ICl,swell. The importance of sulfhydryl groups was confirmed by demonstrating irreversible block by N-ethylmaleimide, a sulfhydryl alkylating reagent. In contrast, nickel failed to block ICl,swell, and as noted in previous studies, cadmium preferentially blocked the time-dependent component of ICl,swell. These data confirm the importance of sulfhydryl groups in the function of ICl,swell. Moreover, by demonstrating the voltage-dependence of block, the data strongly suggest the critical sulfhydryl group is within the channel pore. These biophysical characteristics of native ICl,swell are markers that should be recapitulated in expressed proteins claimed to be responsible for ICl,swell.

This thesis discusses spin-transfer torques in MgO-based magnetic tunnel junctions. The voltage-field switching phase diagrams have been experimentally determined for in-plane CoFeB/MgO/CoFeB magnetic tunnel junctions. In order to limit the effect of thermal activation, experiments have been carried out using nanosecond voltage pulses, as well as at low-temperature (4.2 K). The bias-dependence of the two spin-torque terms (Slonczewski-like and field-like) has been determined from thermally-excited ferromagnetic resonance measurements, yielding values which are in good agreement with previous reports. Additionally, material parameters such as the effective magnetisation and the damping factor have also been extracted. Using these values as input, the switching voltages as function of the applied magnetic field have been calculated numerically and analytically by solving the modified Landau-Lifshitz-Gilbert equation. Unlike previous studies, the field-like spin-torque has also been included. Moreover, different configurations have been considered for the magnetic anisotropy directions of the reference and free layer, respectively. / Diese Arbeit befasst sich mit Spin-Transfer-Torque-Effekten in MgO-basierten magnetischen Tunnelstrukturen. Die Phasendiagramme als Funktion von Spannung und Magnetfeld von CoFeB/MgO/CoFeB-Tunnelstrukturen mit Magnetisierung in der Ebene wurden experimentell bestimmt. Um thermische Anregungseffekte zu limitieren, wurden die Experimente einerseits mit nanosekundenlangen Spannungspulsen und andererseits bei niedrigen Temperaturen (4.2 K) durchgeführt. Die Spannungsabhängigkeit der beiden Spin-Torque-Parameter (in-plane und senkrechter Spin-Transfer-Torque) wurde aus Messungen der thermisch angeregten ferromagnetischen Resonanz bestimmt, wobei sich Werte ergaben, die gut mit vorangegangenen Untersuchungen übereinstimmen. Zusätzlich wurden Werte für Materialparameter wie die effektive Magnetisierung und den Dämpfungsparameter gewonnen. Unter Verwendung der erhaltenen Werte wurden die Schaltspannungen als Funktion des angelegten Magnetfeldes analytisch und numerisch berechnet, indem die erweiterte Landau-Lifshitz-Gilbert-Gleichung gelöst wurde. Im Gegensatz zu vorangegangenen Untersuchungen wurde der senkrechte Spin-Transfer-Torque dabei mit einbezogen. Darüber hinaus wurden verschiedene Konfigurationen für die Richtung der magnetischen Anisotropie der freien und fixierten Schicht berücksichtigt.

This thesis discusses spin-transfer torques in MgO-based magnetic tunnel junctions. The voltage-field switching phase diagrams have been experimentally determined for in-plane CoFeB/MgO/CoFeB magnetic tunnel junctions. In order to limit the effect of thermal activation, experiments have been carried out using nanosecond voltage pulses, as well as at low-temperature (4.2 K). The bias-dependence of the two spin-torque terms (Slonczewski-like and field-like) has been determined from thermally-excited ferromagnetic resonance measurements, yielding values which are in good agreement with previous reports. Additionally, material parameters such as the effective magnetisation and the damping factor have also been extracted. Using these values as input, the switching voltages as function of the applied magnetic field have been calculated numerically and analytically by solving the modified Landau-Lifshitz-Gilbert equation. Unlike previous studies, the field-like spin-torque has also been included. Moreover, different configurations have been considered for the magnetic anisotropy directions of the reference and free layer, respectively.:1 Introduction 2 Fundamentals 2.1 Magnetoresistance 2.1.1 Giant magnetoresistance 2.1.2 Tunnel magnetoresistance 2.2 Spin-transfer torque effect 2.2.1 Physical picture of the STT 2.2.2 In-plane and perpendicular STT 2.3 Equation of motion for the magnetisation 2.3.1 The Landau-Lifshitz-Gilbert equation 2.3.2 Extension including spin-transfer-torque (LLGS) 2.4 Applications of MR and spin-transfer torque 2.4.1 Read heads in hard disk drives 2.4.2 Spin-transfer torque magnetic random access memory 2.5 STT effects in magnetic tunnel junctions 2.5.1 Current-induced switching 2.5.2 Magnetisation precession 2.5.3 Bias-dependence of STT 2.5.4 Back-hopping 3 Experimental 3.1 Samples 3.1.1 Stack composition 3.1.2 Properties of samples used in this work 3.2 Experimental setup 3.2.1 Overview of equipment for the different measurement techniques 3.2.2 Electromagnet and Kepco power supply 3.2.3 Contacting of the sample 3.2.4 Principle specifications of equipment 3.3 Experimental techniques 3.3.1 Measurement of DC R-H and R-I loops 3.3.2 Measurement of phase diagrams: off and on-pulse 3.3.3 Thermally-excited ferromagnetic resonance 4 Results and discussion 4.1 Switching phase diagrams of MTJs 4.1.1 Theory: Calculating the phase diagram 4.1.2 Experimental phase diagrams 4.2 Thermally excited ferromagnetic resonance 4.2.1 Smoothing and fitting of raw data 4.2.2 Determination of Ms 4.2.3 Signal evolution with bias voltage 4.2.4 Analysis of peak position: perpendicular STT 4.2.5 Analysis of peak linewidth 5 Summary and outlook A Appendix List of figures List of tables Bibliography / Diese Arbeit befasst sich mit Spin-Transfer-Torque-Effekten in MgO-basierten magnetischen Tunnelstrukturen. Die Phasendiagramme als Funktion von Spannung und Magnetfeld von CoFeB/MgO/CoFeB-Tunnelstrukturen mit Magnetisierung in der Ebene wurden experimentell bestimmt. Um thermische Anregungseffekte zu limitieren, wurden die Experimente einerseits mit nanosekundenlangen Spannungspulsen und andererseits bei niedrigen Temperaturen (4.2 K) durchgeführt. Die Spannungsabhängigkeit der beiden Spin-Torque-Parameter (in-plane und senkrechter Spin-Transfer-Torque) wurde aus Messungen der thermisch angeregten ferromagnetischen Resonanz bestimmt, wobei sich Werte ergaben, die gut mit vorangegangenen Untersuchungen übereinstimmen. Zusätzlich wurden Werte für Materialparameter wie die effektive Magnetisierung und den Dämpfungsparameter gewonnen. Unter Verwendung der erhaltenen Werte wurden die Schaltspannungen als Funktion des angelegten Magnetfeldes analytisch und numerisch berechnet, indem die erweiterte Landau-Lifshitz-Gilbert-Gleichung gelöst wurde. Im Gegensatz zu vorangegangenen Untersuchungen wurde der senkrechte Spin-Transfer-Torque dabei mit einbezogen. Darüber hinaus wurden verschiedene Konfigurationen für die Richtung der magnetischen Anisotropie der freien und fixierten Schicht berücksichtigt.:1 Introduction 2 Fundamentals 2.1 Magnetoresistance 2.1.1 Giant magnetoresistance 2.1.2 Tunnel magnetoresistance 2.2 Spin-transfer torque effect 2.2.1 Physical picture of the STT 2.2.2 In-plane and perpendicular STT 2.3 Equation of motion for the magnetisation 2.3.1 The Landau-Lifshitz-Gilbert equation 2.3.2 Extension including spin-transfer-torque (LLGS) 2.4 Applications of MR and spin-transfer torque 2.4.1 Read heads in hard disk drives 2.4.2 Spin-transfer torque magnetic random access memory 2.5 STT effects in magnetic tunnel junctions 2.5.1 Current-induced switching 2.5.2 Magnetisation precession 2.5.3 Bias-dependence of STT 2.5.4 Back-hopping 3 Experimental 3.1 Samples 3.1.1 Stack composition 3.1.2 Properties of samples used in this work 3.2 Experimental setup 3.2.1 Overview of equipment for the different measurement techniques 3.2.2 Electromagnet and Kepco power supply 3.2.3 Contacting of the sample 3.2.4 Principle specifications of equipment 3.3 Experimental techniques 3.3.1 Measurement of DC R-H and R-I loops 3.3.2 Measurement of phase diagrams: off and on-pulse 3.3.3 Thermally-excited ferromagnetic resonance 4 Results and discussion 4.1 Switching phase diagrams of MTJs 4.1.1 Theory: Calculating the phase diagram 4.1.2 Experimental phase diagrams 4.2 Thermally excited ferromagnetic resonance 4.2.1 Smoothing and fitting of raw data 4.2.2 Determination of Ms 4.2.3 Signal evolution with bias voltage 4.2.4 Analysis of peak position: perpendicular STT 4.2.5 Analysis of peak linewidth 5 Summary and outlook A Appendix List of figures List of tables Bibliography