The spin Hall effect induces spin currents in nonmagnetic layers, which can control the magnetization of neighbouring ferromagnets. The transparency of the interface is shown to strongly influence the efficiency of such manipulation.

Role of transparency of platinum–ferromagnet interfaces in determining the intrinsic magnitude of the spin Hall effect

X-ray magnetic circular dichroism-A versatile tool to study magnetism

This paper presents a comprehensive critical overview of fundamental and practical aspects of the modern stripline broadband ferromagnetic resonance (BFMR) spectroscopy largely employed for the characterisation of magnetic low-dimensional systems, such as thin ferro- and ferromagnetic, multiferroic and half-metallic films, multi-layers and nanostructures. These planar materials form the platform of the nascent fields of magnonics and spintronics. Experimental and theoretical results of research on these materials are summarised, along with systematic description of various phenomena associated with the peculiarities of the stripline BFMR, such as the geometry of stripline transducers, the orientation of the static magnetic field, the presence of microwave eddy currents, and the impacts of non-magnetic layers, interfaces and surfaces in the samples. Results from 240 articles, textbooks and technical reports are presented and many practical examples are discussed in detail. This review will be of interest to both general physical audience and specialists conducting research on various aspects of magnetisation dynamics and nanomagnetism.

/pdf/broadband-stripline-ferromagnetic-resonance-spectroscopy-of-1at9ae3yp6.pdf

Broadband stripline ferromagnetic resonance spectroscopy of ferromagnetic films, multilayers and nanostructures

An integrated voltage regulator (IVR) is presented that uses custom fabricated thin-film magnetic power inductors. The inductors are fabricated on a silicon interposer and integrated with a multi-phase buck converter IC by 2.5D chip stacking. Several inductor design variations have been fabricated and tested. The best performance has been achieved with a set of eight coupled inductors that each occupies 0.245 mm2 and provides 12.5 nH with 270 mΩ DC. With early inductor prototypes, the IVR efficiency for a 1.8 V:1.0 V conversion ratio peaks at 71% with FEOL current density of 10.8 A/mm2 and inductor current density of 1.53 A/mm2. At maximum load current, 69% conversion efficiency and 1.8 V:1.2 V conversion ratio the FEOL current density reaches 22.6 A/mm2 and inductor current density reaches 3.21 A/mm2.

/pdf/a-2-5d-integrated-voltage-regulator-using-coupled-magnetic-58zdw41sgs.pdf

A 2.5D Integrated Voltage Regulator Using Coupled-Magnetic-Core Inductors on Silicon Interposer

The creation of large magnetic fields is a necessary component in many technologies, ranging from magnetic resonance imaging, electric motors and generators, and magnetic hard disk drives in information storage. This is typically done by inserting a ferromagnetic pole piece with a large magnetisation density MS in a solenoid. In addition to large MS, it is usually required or desired that the ferromagnet is magnetically soft and has a Curie temperature well above the operating temperature of the device. A variety of ferromagnetic materials are currently in use, ranging from FeCo alloys in, for example, hard disk drives, to rare earth metals operating at cryogenic temperatures in superconducting solenoids. These latter can exceed the limit on MS for transition metal alloys given by the Slater-Pauling curve. This article reviews different materials and concepts in use or proposed for technological applications that require a large MS, with an emphasis on nanoscale material systems, such as thin and ultra-thin films. Attention is also paid to other requirements or properties, such as the Curie temperature and magnetic softness. In a final summary, we evaluate the actual applicability of the discussed materials for use as pole tips in electromagnets, in particular, in nanoscale magnetic hard disk drive read-write heads; the technological advancement of the latter has been a very strong driving force in the development of the field of nanomagnetism.

/pdf/a-review-of-high-magnetic-moment-thin-films-for-microscale-mhfn2l7x2f.pdf

A review of high magnetic moment thin films for microscale and nanotechnology applications

Design and partial microfabrication of a coupled power inductor is presented for use in high power-density integrated voltage regulators (IVR). The proposed inductor uses many laminations of uniaxial, high-permeability magnetic material where the orientation of anisotropy between successive laminations is rotated to provide an effectively isotropic core. The high permeability core allows for an inductance density of 200nH/mm2, while coupling between phases prevents magnetic saturation and allows a current density as high as 11A/mm2 according to quasi-static finite-element-analysis (FEA) simulations. The coupling factor, inductance and resistance of the device are optimized for operation in a four-phase integrated buck converter switching at 100MHz.

http://bioeeserv.ee.columbia.edu/downloads/2012/APEC_2011_final.pdf

Design of coupled power inductors with crossed anisotropy magnetic core for integrated power conversion

The internal phase profile of electromagnetic radiation determines many functional properties of metal, oxide or semiconductor heterostructures. In magnetic heterostructures, emerging spin electron ...

/pdf/detection-of-microwave-phase-variation-in-nanometre-scale-psoll86s67.pdf

Detection of microwave phase variation in nanometre-scale magnetic heterostructures

We report submicron imaging (∼0.75 μm resolution) of complex magnetic susceptibility in a micron-size ferromagnetic heterostructure using time-resolved scanning transmission x-ray microscopy. The real and imaginary parts of the susceptibility are extracted from the phase and amplitude of the small-angle (<20°) rotational response of the local magnetization under microwave excitation. Frequency-dependent response patterns were observed in an incompletely saturated bilayer element. The technique is extensible to higher frequencies (to ∼10 GHz), better spatial resolution, and layer-specific measurement.

Sub-micron mapping of GHz magnetic susceptibility using scanning transmission x-ray microscopy

We demonstrate efficient second-harmonic generation at moderate input power for thin film Ni81Fe19 undergoing ferromagnetic resonance (FMR). Powers of the generated second-harmonic are shown to be quadratic in input power, with an upconversion ratio three orders of magnitude higher than that demonstrated in ferrite. The second harmonic signal generated exhibits a significantly lower linewidth than that predicted by low-power Gilbert damping, and is excited without threshold. Results are in good agreement with an analytic, approximate expansion of the Landau-Lifshitz-Gilbert (LLG) equation.

High-efficiency GHz frequency doubling without power threshold in thin-film Ni81Fe19

Four-turn coupled (flux-closed) inductor structures have been fabricated and tested for use in high-power-density integrated voltage regulator (IVR) applications. Our solenoid-like structure is comprised of a laminated magnetic core of four rungs surrounded by four Cu windings creating four coupled inductors. The magnetic core is made of laminations of ultra-high-vacuum-sputtered [5 nm Ta/200 nm Co91.5Zr4.0Ta4.5(CZT)/7 nm SiO2] repeated 20 times. Individual CZT layers are deposited under a magnetic bias to induce uniaxial anisotropy. The quad-coupled inductor shows a frequency response with a measured self-inductance of 7.4 nH for one inductor sustained up to 100 MHz and roll-off to half this low-frequency value at ~450 MHz. This inductance is more than 65× higher than what would be calculated from an air-core inductor of equivalent geometry.

Cheng Cheng

Papers

Design of coupled power inductors with crossed anisotropy magnetic core for integrated power conversion

Detection of microwave phase variation in nanometre-scale magnetic heterostructures

Sub-micron mapping of GHz magnetic susceptibility using scanning transmission x-ray microscopy

High-efficiency GHz frequency doubling without power threshold in thin-film Ni81Fe19

Coupled Inductors With Crossed Anisotropy ${\rm CoZrTa/SiO}_{2}$ Multilayer Cores