Periodic chiral magnetic domains in single-crystal nickel nanowires

We report on experimental and computational investigations of the domain structure of ~0.2 x 0.2 x 8 {\mu}m single-crystal Ni nanowires (NWs). The Ni NWs were grown by a thermal chemical vapor deposition technique that results in highly-oriented single-crystal structures on amorphous SiOx coated Si substrates. Magnetoresistance measurements of the Ni NWs suggest the average magnetization points largely off the NW long axis at zero field. X-ray photoemission electron microscopy images show a well-defined periodic magnetization pattern along the surface of the nanowires with a period of {\lambda} = 250 nm. Finite element micromagnetic simulations reveal that an oscillatory magnetization configuration with a period closely matching experimental observation ({\lambda} = 240 nm) is obtainable at remanence. This magnetization configuration involves a periodic array of alternating chirality vortex domains distributed along the length of the NW. Vortex formation is attributable to the cubic anisotropy of the single crystal Ni NW system and its reduced structural dimensions. The periodic alternating chirality vortex state is a topologically protected metastable state, analogous to an array of 360{\deg} domain walls in a thin strip. Simulations show that other remanent states are also possible, depending on the field history. Effects of material properties and strain on the vortex pattern are investigated. It is shown that at reduced cubic anisotropy vortices are no longer stable, while negative uniaxial anisotropy and magnetoelastic effects in the presence of compressive biaxial strain contribute to vortex formation.Comment: 15 pages, 11 figure

The effect of mirabegron on energy expenditure and brown adipose tissue in healthy lean South Asian and Europid men

Aim: To compare the effects of cold exposure and the β3-adrenergic receptor agonist mirabegron on plasma lipids, energy expenditure and brown adipose tissue (BAT) activity in South Asians versus Europids. Materials and Methods: Ten lean Dutch South Asian (aged 18-30 years; body mass index [BMI] 18-25 kg/m2 ) and 10 age- and BMI-matched Europid men participated in a randomized, double-blinded, cross-over study consisting of three interventions: short-term (~ 2 hours) cold exposure, mirabegron (200 mg one dose p.o.) and placebo. Before and after each intervention, we performed lipidomic analysis in serum, assessed resting energy expenditure (REE) and skin temperature, and measured BAT fat fraction by magnetic resonance imaging. Results: In both ethnicities, cold exposure increased the levels of several serum lipid species, whereas mirabegron only increased free fatty acids. Cold exposure increased lipid oxidation in both ethnicities, while mirabegron increased lipid oxidation in Europids only. Cold exposure and mirabegron enhanced supraclavicular skin temperature in both ethnicities. Cold exposure decreased BAT fat fraction in both ethnicities. After the combination of data from both ethnicities, mirabegron decreased BAT fat fraction compared with placebo. Conclusions: In South Asians and Europids, cold exposure and mirabegron induced beneficial metabolic effects. When combining both ethnicities, cold exposure and mirabegron increased REE and lipid oxidation, coinciding with a higher supraclavicular skin temperature and lower BAT fat fraction.Diabetes Research Foundation Fellowship 2015.81.1808Netherlands CardioVascular Research Initiative: 'the Dutch Heart Foundation, Dutch Federation of University Medical Centers, the Netherlands Organisation for Health Research and Development and the Royal Netherlands Academy of Sciences' CVON2014-02 ENERGISE CVON2017-20 GENIUS-IIEuropean Union (EU) 602485European Research Council (NOMA-MRI) PCNR is an Established Investigator of the Netherlands Heart Foundation 2009T03

Comparative oncology and clinical translation of glyco protein conjugated gold nano therapeutic agent (GA-198AuNP) [abstract]

Nanoscience Poster SessionAs part of our efforts toward clinical translation of GA-198AuNP, our studies are focused on therapeutic efficacy of nanoparticulate GA198AuNP agent in dogs with prostatic carcinoma. The overall goal is to gain clinical insights on therapeutic efficacy of GA198AuNP in a large animal model. We have performed a phase I clinical trial using GA-AuNP administered intravenously or intratumorally by injection or infusion. CT scans were performed prior to injection and 24 hours post injection in 3 of the 4 dogs. Following injections, dogs were allowed further treatment as recommended by the primary attending clinician. Four dogs have been treated to date. Complications related to GA-AuNP treatment were not observed, and all 4 dogs received adjunctive treatment with radiation therapy and/ or chemotherapy. These preliminary studies have clearly provided compelling evidence on the therapeutic potential of biocompatible GA-AuNP for their utility as novel therapeutic agents in treating various types of inoperable solid tumors. Intra-tumoral and intravenous administration of GA-AuNP is safe in dogs with spontaneously occurring tumors. As further therapeutic efficacy studies continue, the outcome of this clinical trial in a large animal model will generate therapeutic efficacy data which will be used for filing IND application for Phase I clinical trial studies. This clinical translation effort provides significant advances in terms of delivering optimum therapeutic payloads into prostate cancers with subsequent reduction in tumor volume, thus may effectively reduce/eliminate the need for surgical resection. This presentation will include details of clinical translation of GA198AuNP in prostate tumor bearing dogs

Engineering of Metallic Multilayers and Spin Transfer Torque Devices /

This dissertation explores in detail the nanofabrication and characterization of ultrathin metallic multilayers designed for the study of several electronic, magnetic, and optical phenomena. Several topics are covered, but the primary focus lies in the investigation and optimization of various sputter deposited thin-film structures with perpendicular magnetic anisotropy (PMA) for their incorporation into MgO-based magnetic tunnel junctions (MTJ). MTJs with these materials systems can then be ultimately applied towards functional spin-transfer-torque magnetoresistive RAM (STT-MRAM) technologies. As multiple topics are to be covered, this dissertation is roughly sub -divided into two parts: (i) full film materials investigation and (ii) device level characterization. (i) Full films materials investigation involved the exploration and optimization of multilayer systems such as Co/Pt, Co/Ni, and Co/Pd as well as crystalline alloys such as CoFeB and CoCrPt. Once identified, these materials were used in the development of perpendicular synthetic antiferromagnet (pSAF) systems. A separate study was performed to evaluate the free layers in pMTJ thin film stacks, focusing on substrate, deposition, and capping effects that contribute to interfacial PMA in MgO/CoFeB- like systems. (ii) A variety of magnetotransport techniques were implemented to study current-induced magnetic reversal of both in-plane and perpendicular MRAM MTJs. The set of magnetotransport tools developed includes both quasi-static field/current methods as well as high- speed transport techniques and have been used to probe key parameters of MRAM cells such as switching voltage, energy barrier, bit-error rates, and spin-torque efficiency. A population of MTJs was studied to analyze the behavior of normal and tail-bit devices. It was discovered through low -temperature magnetotransport measurements that these tail bit MTJs are prone to nucleation of metastable intermediate states and have poor spin-filtering capabilities. Several sizes of perpendicular MTJs were characterized by electrical stress and field sweeping techniques and found to have a variety of defects based on poor MgO/CoFeB interfacial anisotropy. The importance of proper MgO/CoFeB interface engineering is also emphasized in this section as it affects so many of the measurable metrics by which we gauge STT-MRAM as a viable technolog

Engineering of Metallic Multilayers and Spin Transfer Torque Devices /

This dissertation explores in detail the nanofabrication and characterization of ultrathin metallic multilayers designed for the study of several electronic, magnetic, and optical phenomena. Several topics are covered, but the primary focus lies in the investigation and optimization of various sputter deposited thin-film structures with perpendicular magnetic anisotropy (PMA) for their incorporation into MgO-based magnetic tunnel junctions (MTJ). MTJs with these materials systems can then be ultimately applied towards functional spin-transfer-torque magnetoresistive RAM (STT-MRAM) technologies. As multiple topics are to be covered, this dissertation is roughly sub -divided into two parts: (i) full film materials investigation and (ii) device level characterization. (i) Full films materials investigation involved the exploration and optimization of multilayer systems such as Co/Pt, Co/Ni, and Co/Pd as well as crystalline alloys such as CoFeB and CoCrPt. Once identified, these materials were used in the development of perpendicular synthetic antiferromagnet (pSAF) systems. A separate study was performed to evaluate the free layers in pMTJ thin film stacks, focusing on substrate, deposition, and capping effects that contribute to interfacial PMA in MgO/CoFeB- like systems. (ii) A variety of magnetotransport techniques were implemented to study current-induced magnetic reversal of both in-plane and perpendicular MRAM MTJs. The set of magnetotransport tools developed includes both quasi-static field/current methods as well as high- speed transport techniques and have been used to probe key parameters of MRAM cells such as switching voltage, energy barrier, bit-error rates, and spin-torque efficiency. A population of MTJs was studied to analyze the behavior of normal and tail-bit devices. It was discovered through low -temperature magnetotransport measurements that these tail bit MTJs are prone to nucleation of metastable intermediate states and have poor spin-filtering capabilities. Several sizes of perpendicular MTJs were characterized by electrical stress and field sweeping techniques and found to have a variety of defects based on poor MgO/CoFeB interfacial anisotropy. The importance of proper MgO/CoFeB interface engineering is also emphasized in this section as it affects so many of the measurable metrics by which we gauge STT-MRAM as a viable technolog

Engineering of Metallic Multilayers and Spin Transfer Torque Devices /

This dissertation explores in detail the nanofabrication and characterization of ultrathin metallic multilayers designed for the study of several electronic, magnetic, and optical phenomena. Several topics are covered, but the primary focus lies in the investigation and optimization of various sputter deposited thin-film structures with perpendicular magnetic anisotropy (PMA) for their incorporation into MgO-based magnetic tunnel junctions (MTJ). MTJs with these materials systems can then be ultimately applied towards functional spin-transfer-torque magnetoresistive RAM (STT-MRAM) technologies. As multiple topics are to be covered, this dissertation is roughly sub -divided into two parts: (i) full film materials investigation and (ii) device level characterization. (i) Full films materials investigation involved the exploration and optimization of multilayer systems such as Co/Pt, Co/Ni, and Co/Pd as well as crystalline alloys such as CoFeB and CoCrPt. Once identified, these materials were used in the development of perpendicular synthetic antiferromagnet (pSAF) systems. A separate study was performed to evaluate the free layers in pMTJ thin film stacks, focusing on substrate, deposition, and capping effects that contribute to interfacial PMA in MgO/CoFeB- like systems. (ii) A variety of magnetotransport techniques were implemented to study current-induced magnetic reversal of both in-plane and perpendicular MRAM MTJs. The set of magnetotransport tools developed includes both quasi-static field/current methods as well as high- speed transport techniques and have been used to probe key parameters of MRAM cells such as switching voltage, energy barrier, bit-error rates, and spin-torque efficiency. A population of MTJs was studied to analyze the behavior of normal and tail-bit devices. It was discovered through low -temperature magnetotransport measurements that these tail bit MTJs are prone to nucleation of metastable intermediate states and have poor spin-filtering capabilities. Several sizes of perpendicular MTJs were characterized by electrical stress and field sweeping techniques and found to have a variety of defects based on poor MgO/CoFeB interfacial anisotropy. The importance of proper MgO/CoFeB interface engineering is also emphasized in this section as it affects so many of the measurable metrics by which we gauge STT-MRAM as a viable technolog

ParamagneticFexTa1-x alloys for engineering of perpendicularly magnetized tunnel junctions

Abstract: Exchange coupling between two magnetic layers through an interlayer is of broad interest for numerous recent applications of nano-magnetic systems. In this Letter we study ferromagnetic exchange coupling through amorphous paramagnetic Fe-Ta alloys. We show that the exchange coupling depends exponentially on spacer thickness and scales with the Fe-Ta susceptibility, which can be tuned via the alloy composition and/or temperature. Such materials are of high interest for the engineering of perpendicularly magnetized CoFeB-MgO based tunnel junctions as it enables ferromagnetic coupling of magnetic layers with differing crystalline lattices, suppresses dead layers and can act as an inter-diffusion barrier during annealing. Author to whom correspondence should be addressed