Stripline (SL), vector network analyzer (VNA), and pulsed inductive microwave magnetometer (PIMM) techniques were used to measure the ferromagnetic resonance (FMR) linewidth for a series of Permalloy films with thicknesses of 50 and 100nm. The SL-FMR measurements were made for fixed frequencies from 1.5to5.5GHz. The VNA-FMR and PIMM measurements were made for fixed in-plane fields from 1.6to8kA∕m (20–100Oe). The results provide a confirmation, lacking until now, that the linewidths measured by these three methods are consistent and compatible. In the field format, the linewidths are a linear function of frequency, with a slope that corresponds to a nominal Landau-Lifshitz phenomenological damping parameter α value of 0.007 and zero frequency intercepts in the 160–320A∕m (2–4Oe) range. In the frequency format, the corresponding linewidth versus frequency response shows a weak upward curvature at the lowest measurement frequencies and a leveling off at high frequencies.

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Ferromagnetic resonance linewidth in metallic thin films: Comparison of measurement methods | NIST

The damping of magnetization, represented by the rate at which it relaxes to equilibrium, is successfully modeled as a phenomenological extension in the Landau-Lifschitz-Gilbert equation. This is the damping torque term known as Gilbert damping and its direction is given by the vector product of the magnetization and its time derivative. Here we derive the Gilbert term from first principles by a non-relativistic expansion of the Dirac equation. We find that the Gilbert term arises when one calculates the time evolution of the spin observable in the presence of the full spin-orbital coupling terms, while recognizing the relationship between the curl of the electric field and the time varying magnetic induction.

http://absimage.aps.org/image/MAR09/MWS_MAR09-2008-002211.pdf

The origin of intrinsic Gilbert damping

The growing market for sensors, internet of things, and wearable devices is fueling the development of low-cost energy-harvesting materials and systems. Film based thermoelectric (TE) devices offer the ability to address the energy requirements by using ubiquitously available waste-heat. This review narrates recent advancements in fabricating high-performance TE films and superlattice structures, from the aspects of microstructure control, doping, defects, composition, surface roughness, substrate effect, interface control, nanocompositing, and crystal preferred orientation realized by regulating various deposition parameters and subsequent heat treatment. The review begins with a brief account of heat conduction mechanism, quantum confinement effect in periodic layers, film deposition processes, thin film configurations and design consideration for TE in-plane devices, and characterization techniques. It then proceeds to alayzing the latest findingd on the TE properties of Bi2(Te,Se)3 and (Bi,Sb)2Te3, PbTe, GeTe, SnSe, SnTe, Cu2-xSe, and skutterudite films, including superlattices and the performance of TE generators, sensors, and cooling devices. Thickness dependent microstructure evolution and TE characteristics of films in relation to temperature are also analyzed. In the context of spin Seebeck effect (SSE) based systems, SSE mechanism analysis, developments in enhancing the spin Seebeck signal since its first observation, and recent developments are covered from the facets of new system design, signal collection, magnetic manipulation, interface conditions, thickness-dependent longitudinal spin Seebeck signal, and length scale of phonon and magnon transport in longitudinal SSE (LSSE) in different bi-layer systems. At the end, possible strategies for further enhancing zT of TE films and spin Seebeck signals of many systems are addressed.

Thermoelectric films and periodic structures and spin Seebeck effect systems: Facets of performance optimization

Tuning of magnetic properties by alternating the order of hard/soft bilayers with various thicknesses

We present a comprehensive study on the magnetization reversal in the Fe/NiFe bilayer system by alternating the order of the magnetic layers. All the samples show growth-induced uniaxial magnetic anisotropy due to the oblique angle deposition technique. Strong interfacial exchange coupling between the Fe and NiFe layers leads to single-phase hysteresis loops in the bilayer system. The strength of coupling being dependent on the interface changes upon alternating the order of magnetic layers. The magnetic parameters such as coercivity HC, and anisotropy field HK become almost doubled when a NiFe layer is grown over the Fe layers. This enhancement in the magnetic parameters is primarily dependent on the increase of the thickness and magnetic moment of the Fe–NiFe interfacial layer as revealed from the polarized neutron reflectivity (PNR) data of the bilayer samples. The difference in the thickness and magnetization of the Fe–NiFe interfacial layer indicates the modification of the microstructure by alternating the order of the magnetic layers of the bilayers. The interfacial magnetic moment increased by almost 18% when the NiFe layer was grown over the Fe layer. In spite of the different values of anisotropy fields and modified interfacial exchange coupling, the Gilbert damping constant values of the ferromagnetic bilayers remain similar to the single NiFe layer.

/pdf/study-of-the-magnetic-interface-and-its-effect-in-fe-nife-1kc45xcd7x.pdf

Study of the magnetic interface and its effect in Fe/NiFe bilayers of alternating order

Divalent mercury (Hg2+) is highly toxic in nature and extensively found in different natural water bodies worldwide. Thus, rapid trace-level monitoring of Hg2+, as well as its effective removal fro...

Dithia-Crown-Ether Integrated Self-Exfoliated Polymeric Covalent Organic Nanosheets for Selective Sensing and Removal of Mercury

Exchange bias in Fe/Ir20Mn80 bilayers: Role of spin-glass like interface and ‘bulk’ antiferromagnet spins

Exchange bias in ferromagnetic/antiferromagnetic systems can be explained in terms of various interfacial phenomena. Among these spin glass frustration can affect the magnetic properties in exchange bias systems. Here we have studied a NiMn/CoFeB exchange bias system in which spin glass frustration seems to play a crucial role. In order to account the effect of spin glass frustration on magnetic properties, we have performed the temperature and cooling field dependence of exchange bias. We have observed the decrease of exchange bias field (HEB) with cooling field (HFC) whereas there is not significant effect on coercive field (HC). Exponential decay of HEB and HC is found in these exchange bias systems. Further, training effect measurements have been performed to study the spin relaxation mechanism. We have fitted the training effect data with frozen and rotatable spin relaxation model. We have investigated the ratio of relaxation rate of interfacial rotatable and frozen spins in this study. The training effect data are also fitted with various other models. Further, we observed the shifting of peak temperature towards higher temperature with frequency from the ac susceptibility data.

Sagarika Nayak

Papers

Dithia-Crown-Ether Integrated Self-Exfoliated Polymeric Covalent Organic Nanosheets for Selective Sensing and Removal of Mercury

Tuning of magnetic properties by alternating the order of hard/soft bilayers with various thicknesses

Study of the magnetic interface and its effect in Fe/NiFe bilayers of alternating order

Exchange bias in Fe/Ir20Mn80 bilayers: Role of spin-glass like interface and ‘bulk’ antiferromagnet spins

Effect of spin glass frustration on exchange bias in NiMn/CoFeB bilayers