Element-resolved x-ray ferrimagnetic and ferromagnetic resonance spectroscopy

We report on the measurement of element-specific magnetic resonance spectra at gigahertz frequencies using x-ray magnetic circular dichroism (XMCD). We investigate the ferrimagnetic precession of Gd and Fe ions in Gd-substituted Yttrium Iron Garnet, showing that the resonant field and linewidth of Gd precisely coincide with Fe up to the nonlinear regime of parametric excitations. The opposite sign of the Gd x-ray magnetic resonance signal with respect to Fe is consistent with dynamic antiferromagnetic alignment of the two ionic species. Further, we investigate a bilayer metal film, Ni$_{80}$Fe$_{20}$(5 nm)/Ni(50 nm), where the coupled resonance modes of Ni and Ni$_{80}$Fe$_{20}$ are separately resolved, revealing shifts in the resonance fields of individual layers but no mutual driving effects. Energy-dependent dynamic XMCD measurements are introduced, combining x-ray absorption and magnetic resonance spectroscopies.Comment: 16 pages, 8 figure

Microscopic four-point probe based on SU-8 cantilevers

A microscopic four-point probe (u4PP) for resistivity measurements on thin films was designed and fabricated using the negative photoresist SU-8 as base material. The device consists of four microscopic cantilevers, each of them supporting a probe tip at the extremity. The high flexibility of SU-8 ensures a stable electrical point contact between samples and probe tip with all four electrodes even on rough surfaces. With the presented surface micromachining process, u4PPs with a probe-to-probe spacing of 10–20 um were fabricated. Resistivity measurements on thin Au, Al, and Pt films were performed successfully. The measured sheet resistances differ by less than 5% from those obtained by a commercial macroscopic resistivity meter. Due to the low contact forces (Fcont10^6 ohm/

Polymer-based cantilevers with integrated electrodes

An innovative release method of polymer cantilevers with embedded integrated metal electrodes is presented. The fabrication is based on the lithographic patterning of the electrode layout on a wafer surface, covered by two layers of SU-8 polymer: a 10-um-thick photo-structured layer for the cantilever, and a 200-um-thick layer for the chip body. The releasing method is based on dry etching of a 2-um-thick sacrificial polysilicon layer. Devices with complex electrode layout embedded in free-standing 500-um-long and 100-um-wide SU-8 cantilever were fabricated and tested.We have optimized major fabrication steps such as the optimization of the SU-8 chip geometry for reduced residual stress and for enhanced underetching, and by defining multiple metal layers [titanium (Ti), aluminum (Al), bismuth (Bi)] for improved adhesion between metallic electrodes and polymer. The process was validated for a miniature 2x2 um2 Hall-sensor integrated at the apex of a polymer microcantilever for scanning magnetic field sensing. The cantilever has a spring constant of =1 N/m and a resonance frequency of=17 kHz. Galvanometric characterization of the Hall sensor showed an input/output resistance of 200 ohm, a device sensitivity of 0.05 V/AT and a minimum detectable magnetic flux density of 9 uT/Hz^1/2 at frequencies above 1 kHz at room temperature. Quantitative magnetic field measurements of a microcoil were performed. The generic method allows for a stable integration of electrodes into polymers MEMS and it can readily be used for other types of microsensors where conducting metal electrodes are integrated in cantilevers for advanced scanning probe sensing applications.LMIS3LMIS

Combined Al-protection and HF-vapor release process for ultrathin single crystal silicon cantilevers

A new technology based on a combination of Al-protection layers and HF-vapor etching to produce ultrathin single crystal silicon cantilevers is presented. 500 um long, 10 um wide and 0.5 um thick cantilevers have been fabricated with a high yield. A resonance frequency of 2 kHz, Q factor >100,000 and a force sensitivity of 6.0 x 10^17 N/Hz^1/2 have been obtained in vacuum at room temperature for cantilevers annealed at 800 degrees C

Submicrometer Hall devices fabricated by focused electron-beam-induced deposition

Hall devices having an active area of about (500 nm)(2) are fabricated by focused electron-beam-induced deposition. The deposited material consists of cobalt nanoparticles in a carbonaceous matrix. The realized devices have, at room temperature, a current sensitivity of about 1 V/AT, a resistance of a few kilo-ohms, and can be biased with a maximum current of about 1 mA. The room-temperature magnetic field resolution is about 10 muT/Hz(1/2) at frequencies above 1 kHz

14 GHz longitudinally detected electron spin resonance using microHall sensors

In this work we developed a home-made LOngitudinally Detected Electron Spin Resonance (LODESR) spectrometer based on a microsize Hall sensor. A coplanar waveguide (CPW)-resonator is used to induce microwave-excitation on the sample at 14 GHz. We used InSb cross-shaped Hall devices with active areas of (10 mu m x 10 mu m) and (5 mu m x 5 mu m). Signal intensities of the longitudinal magnetization component of DPPH and YIG samples of volumes about (10 mu m)(3) and (5 mu m)(3), are measured under amplitude and frequency modulated microwave magnetic field generated by the CPW-resonator. At room temperature, 10(9) spins/G root Hz sensitivity is achieved for 0.2 mT linewidth, a result which is still better than most of inductive detected LODESR sensitivities. (C) 2017 Elsevier Inc. All rights reserved

MICRO-HALL SENSORS ON SU-8 CANTILEVERS FOR MAGNETIC IMAGINIG

Micro-Hall sensors made of Bi have been previously fabricated and have shown interesting properties for magnetic field detection. In this project, new ideas to improve the performance of these Hall sensors and to explore ferromagnetic metals are developed. Ni and Bi protected with Al2O3 are used as materials to realize the sensing element. Different thicknesses between 10 and 100 nm of Ni and Bi are deposited by evaporation and structured with lift-off. The electrodes are made of Ti/Al. A Pt thin film is deposited between the sensor and the electrodes to improve electrical contact. Two SU-8 layers are structured with the standard photolithography process to build a cantilever and a carrier chip. Release of the sensor chip is performed with ICP SF6 plasma to etch the poly-Silicon layer

Bismuth Hall Sensors on Plastic Cantilevers

Innovative surface imaging techniques allowing parallel magnetic and topographical microscopy with nanometer scale spatial resolution are developed in this project. Nanometer scale magnetosensitive devices on Atomic Force Microscopy (AFM) tips will be studied and fabricated, allowing quantitative and noninvasive magnetic field imaging with spatial resolution better than 100 nm and magnetic field resolution better than 100 mT/Hz. Such performance will allow one to perform magnetic microscopy studies, which are impossible with present magnetic imaging techniques. Magnetic imaging with spatial resolution better than 100 nm is currently performed by magnetic force microscopy (MFM). However, the MFM technique has three major drawbacks: it is hardly quantitative, invasive, and not fully "decoupled" from the AFM topography. The approach proposed in this project allows quantitative, more sensitive and non-invasive magnetic field measurements. Additionally, totally "decoupled" parallel AFM imaging is possible