Thermoelectric effects in magnetic nanostructures

Elektronentransport is een belangrijk natuurkundig verschijnsel dat vaak wordt gebruikt in de hedendaagse technologie. Alle elektrische apparaten, variërend van stofzuigers tot computerchips, zijn in principe gebaseerd op dit type transport. Ondanks dat elektronen meerdere eigenschappen hebben, wordt in de praktijk echter vaak alleen de lading van het elektron gebruikt. De energie en het magnetisch moment van de elektronen zijn eigenschappen die in respectievelijk thermoelektriciteit en spin-elektronica (afgekort: spintronica) worden toegepast. Spintronica richt zich op de overdracht van het magnetisch moment om bijvoorbeeld informatie te transporteren, terwijl thermoelektrische verschijnselen, zoals het Peltier en Seebeck effect, toegepast kunnen worden voor elektrische verwarming/koeling en thermokoppels. Dit proefschrift beschrijft de fundamentele interacties tussen de drie vormen van transport (lading, warmte en spin) in magnetische nanostructuren. Het experimentele werk is een onderdeel van een breder onderzoeksgebied dat spin-caloritronica wordt genoemd. Deze onderzoeksrichting binnen de spintronica bestudeert de rol van het magnetisch moment van elektronen in warmtetransport. De meerwaarde van deze spin-caloritronische effecten ligt, ten opzichte van reguliere thermoelektrische verschijnselen, in het gemak van het controleren van de magnetische textuur op de nanoschaal. Dit biedt daarom een sterk gelokaliseerde en programmeerbare controle over warmtestromen en zou bruikbaar kunnen zijn voor het genereren van thermo-elektrische energie of voor koeling. De gemeten effecten zijn echter klein en zijn nog ver weg van directe toepassingen. Desalniettemin zouden nieuwe ontwikkelingen binnen dit onderzoeksveld op een dag kunnen leiden tot de implementatie van spin-caloritronica in onze dagelijkse elektronische apparatuur. Electron transport is one of the most important physical phenomena used in todays technology. All modern electrical equipment, ranging from vacuum cleaners till high-end microprocessors is essentially founded on this type of transport. However, in most cases the electron's full potential is not used and most applications only exploit the negative elementary charge that it possesses. The energy and the magnetic moment of the electrons are properties which are used in thermoelectricity and spin-electronics (spintronics), respectively. Spintronics focuses on the transfer of magnetic moments for the information transport, while thermoelectric phenomena (e.g. the Peltier and Seebeck effect) have found their application in devices for electric heating/cooling or thermocouples. This thesis describes the fundamental interactions between the three types of transport (charge, heat, spin) in magnetic nanostructures. The experimental work described here is part of a wider research direction, called spin-caloritronics. This research branch of spintronics studies the role of magnetic moments in heat transport. The potential advantages of spin-caloritronic effects with respect to regular thermoelectricity can be found in the easy manipulation of magnetic textures at the nanoscale. This enables very localized and programmable control of heat flow which might prove useful for thermopower energy harvesting or refrigeration. However, the previously discussed effects are weak and far from direct applications. Nonetheless, a combination of new developments in this field and by exploring novel materials it could one day lead to the implementation of spin-caloritronics in our everyday electronic devices.

Thermal spin transport and spin-orbit interaction in ferromagnetic/non-magnetic metals

In this article we extend the currently established diffusion theory of spin-dependent electrical conduction by including spin-dependent thermoelectricity and thermal transport. Using this theory, we propose new experiments aimed at demonstrating novel effects such as the spin-Peltier effect, the reciprocal of the recently demonstrated thermally driven spin injection, as well as the magnetic heat valve. We use finite-element methods to model specific devices in literature to demonstrate our theory. Spin-orbit effects such as anomalous-Hall, -Nernst, anisotropic magnetoresistance and spin-Hall are also included in this model

Anomalous Nernst and anisotropic magnetoresistive heating in a lateral spin valve

We measured the anomalous Nernst effect and anisotropic magnetoresistive heating in a lateral multiterminal permalloy/copper spin valve using all-electrical lock-in measurements. To interpret the results, a three-dimensional thermoelectric finite-element model is developed. Using this model, we extract the heat profile which we use to determine the anomalous Nernst coefficient of permalloy RN = 0.13 and also determine the maximum angle θ = 8° of the magnetization prior to the switching process when an opposing noncollinear 10° magnetic field is applied.

Adult height and the risk of cause-specific death and vascular morbidity in 1 million people: individual participant meta-analysis.

BACKGROUND: The extent to which adult height, a biomarker of the interplay of genetic endowment and early-life experiences, is related to risk of chronic diseases in adulthood is uncertain. METHODS: We calculated hazard ratios (HRs) for height, assessed in increments of 6.5 cm, using individual-participant data on 174374 deaths or major non-fatal vascular outcomes recorded among 1085949 people in 121 prospective studies. RESULTS: For people born between 1900 and 1960, mean adult height increased 0.5-1 cm with each successive decade of birth. After adjustment for age, sex, smoking and year of birth, HRs per 6.5 cm greater height were 0.97 (95% confidence interval: 0.96-0.99) for death from any cause, 0.94 (0.93-0.96) for death from vascular causes, 1.04 (1.03-1.06) for death from cancer and 0.92 (0.90-0.94) for death from other causes. Height was negatively associated with death from coronary disease, stroke subtypes, heart failure, stomach and oral cancers, chronic obstructive pulmonary disease, mental disorders, liver disease and external causes. In contrast, height was positively associated with death from ruptured aortic aneurysm, pulmonary embolism, melanoma and cancers of the pancreas, endocrine and nervous systems, ovary, breast, prostate, colorectum, blood and lung. HRs per 6.5 cm greater height ranged from 1.26 (1.12-1.42) for risk of melanoma death to 0.84 (0.80-0.89) for risk of death from chronic obstructive pulmonary disease. HRs were not appreciably altered after further adjustment for adiposity, blood pressure, lipids, inflammation biomarkers, diabetes mellitus, alcohol consumption or socio-economic indicators. CONCLUSION: Adult height has directionally opposing relationships with risk of death from several different major causes of chronic diseases