9 research outputs found
Six-fold in-plane magnetic anisotropy in Co-implanted ZnO (0001)
Magnetic anisotropies of Co-implanted ZnO (0001) films grown on
single-crystalline Al2O3 (11-20) substrates have been studied by ferromagnetic
resonance (FMR) technique for different cobalt implantation doses. The FMR data
show that the easy and hard axes have a periodicity of 60 degrees in the film
plane, in agreement with the hexagonal structure of the ZnO films. This
six-fold in-plane magnetic anisotropy, which is observed for the first time in
ZnO-based diluted magnetic semiconductors, is attributed to the substitution of
cobalt on Zn sites in the ZnO structure, and a clear indication for long range
ferromagnetic ordering between substitutional cobalt ions in the
single-crystalline ZnO films.Comment: 7 pages, 4 figure
Coexistence of perpendicular and in-plane exchange bias using a single ferromagnetic layer in Pt/Co/Cr/CoO thin film
We studied the temperature dependence of magnetization and exchange bias in a Pt/Co/Cr/CoO multilayer thin film. These magnetic multilayers are of particular interest since the easy axis of ultra-thin Co is strongly affected by the interfacial anisotropies of neighbouring Pt and Cr layers. The room temperature measurements show that the sample has a magnetic easy axis only in the film plane. However, upon cooling the sample, the easy axis of the magnetization departs from its initial orientation and typical easy-axis hysteresis loops are obtained for both in-plane and perpendicular directions. In accordance with this change in the magnetization direction at lower temperatures, the sample shows an unexpected coexistence of perpendicular and in-plane exchange bias below the antiferromagnetic transition of CoO. The temperature dependence of the exchange bias field for both directions is also significantly different. Along the film plane, the exchange bias field monotonically decreases and disappears at 220 K with increasing temperature. For the perpendicular direction, however, the exchange bias field increases and reaches a maximum value at 80 K. Then it decreases and disappears at 150 K with further increasing temperature. The mechanisms behind this anomalous temperature dependence of the exchange bias as well as the step-like behaviour in the hysteresis curves are discussed. Copyright (C) EPLA, 201
Current trends in planar Hall effect sensors: evolution, optimization, and applications
The advantages of planar Hall effect (PHE) sensors-their thermal stability, very low detection limits, and high sensitivities-have supported a wide range of advanced applications such as nano-Tesla (nT) magnetometers, current sensing, or low magnetic moment detection in lab-on-a-chip devices. In this review we outline the background and implications of these PHE sensors, starting from fundamental physics through their technological evolution over the past few decades. Key parameters affecting the performance of these sensors, including noise from different sources, thermal stability, and magnetoresistance magnitudes are discussed. The progression of sensor geometries and junctions from disk, cross-to-bridge, ring, and ellipse configuration is also reviewed. The logical sequence of these structures from single magnetoresistive layers to bi-, tri-layers, and spin-valves is also covered. Research contributions to the development of these sensors are highlighted with a focus on microfluidics and flexible sensorics. This review serves as a comprehensive resource for scientists who wish to use PHE for fundamental research or to develop new applications and devices. The conclusions from this report will benefit the development, production, and performance evaluation of PHE-based devices and microfluidics, as well as set the stage for future advances.1
Current trends in planar Hall effect sensors: evolution, optimization, and applications
Elzwawy A, Piskin H, Akdogan N, et al. Current trends in planar Hall effect sensors: evolution, optimization, and applications. Journal of Physics D: Applied Physics . 2021;54(35): 353002.The advantages of planar Hall effect (PHE) sensors-their thermal stability, very low detection limits, and high sensitivities-have supported a wide range of advanced applications such as nano-Tesla (nT) magnetometers, current sensing, or low magnetic moment detection in lab-on-a-chip devices. In this review we outline the background and implications of these PHE sensors, starting from fundamental physics through their technological evolution over the past few decades. Key parameters affecting the performance of these sensors, including noise from different sources, thermal stability, and magnetoresistance magnitudes are discussed. The progression of sensor geometries and junctions from disk, cross-to-bridge, ring, and ellipse configuration is also reviewed. The logical sequence of these structures from single magnetoresistive layers to bi-, tri-layers, and spin-valves is also covered. Research contributions to the development of these sensors are highlighted with a focus on microfluidics and flexible sensorics. This review serves as a comprehensive resource for scientists who wish to use PHE for fundamental research or to develop new applications and devices. The conclusions from this report will benefit the development, production, and performance evaluation of PHE-based devices and microfluidics, as well as set the stage for future advances
Dose dependence of ferromagnetism in Co-implanted ZnO
We have studied the structural, magnetic and electronic properties of
Co-implanted ZnO (0001) films grown on Al2O3 (1120) substrates for different
implantation doses and over a wide temperature range. Strong room temperature
ferromagnetism is observed with magnetic parameters depending on the cobalt
implantation dose. A detailed analysis of the structural and magnetic
properties indicates that there are two magnetic phases in Co-implanted ZnO
films. One is a ferromagnetic phase due to the formation of long range
ferromagnetic ordering between implanted magnetic cobalt ions in the ZnO layer,
the second one is a superparamagnetic phase, which occurs due to the formation
of metallic cobalt clusters in the Al2O3 substrate. Using x-ray resonant
magnetic scattering, the element specific magnetization of cobalt, oxygen and
Zn was investigated. Magnetic dichroism was observed at the Co L2,3 edges as
well as at the O K edge. In addition, the anomalous Hall effect is also
observed, supporting the intrinsic nature of ferromagnetism in Co-implanted ZnO
films.Comment: 9 pages, 11 figure
High temperature ferromagnetism in Co-implanted rutile
We report on structural, magnetic and electronic properties of Co-implanted
TiO2 rutile single crystals for different implantation doses. Strong
ferromagnetism at room temperature and above is observed in TiO2 rutile plates
after cobalt ion implantation, with magnetic parameters depending on the cobalt
implantation dose. While the structural data indicate the presence of metallic
cobalt clusters, the multiplet structure of the Co L3 edge in the XAS spectra
gives clear evidence for a substitutional Co 2+ state. The detailed analysis of
the structural and magnetic properties indicates that there are two magnetic
phases in Co-implanted TiO2 plates. One is a ferromagnetic phase due to the
formation of long range ferromagnetic ordering between implanted magnetic
cobalt ions in the rutile phase, and the second one is a superparamagnetic
phase originates from the formation of metallic cobalt clusters in the
implanted region. Using x-ray resonant magnetic scattering, the element
specific magnetization of cobalt, oxygen and titanium in Co-implanted TiO2
single crystals are investigated. Magnetic dichroism was observed at the Co L
edges as well as at the O K edge. The interaction mechanism, which leads to
ferromagnetic ordering of substituted cobalt ions in the host matrix, is also
discussed.Comment: 19 pages, 16 figure