scholarly journals Skyrmion generation and perpendicular magnetic anisotropy modification in Heusler alloy ultrathin films

2021 ◽  
Author(s):  
◽  
Yao Zhang
Keyword(s):  
Thin Films ◽  
Magnetic Properties ◽  
Band Structure ◽  
Magnetic Anisotropy ◽  
Ultrathin Films ◽  
Heusler Alloy ◽  
Anomalous Hall Effect ◽  
Berry Curvature ◽  
Effective Magnetic Anisotropy ◽  
Hall Angle

<p><b>This thesis explores the magnetic properties of Heusler alloy thin films for spintronics applications. The skyrmion generation under different externalstimulation was focused in MgO/Mn2CoAl/Pd ultrathin films and the anomalous Hall effect of Co2MnGa thin films.</b></p> <p>The perpendicularly magnetized MgO/Mn2CoAl/Pd ultrathin films were firstly optimised by changing the thickness of Pd layer so that the effective magnetic anisotropy can be tuned and various magnetic textures can be obtained for different purposes. Based on the understanding of Pd dependence of magnetic properties, The skyrmion generation by applying an in-plane magnetic field was investigated to fine tune the effective magnetic anisotropy. Further the fractal analysis was used to describe the evolution of the magnetic states and categorise the formation of skyrmions. </p> <p>Then skyrmion generation by ionic liquid gating has been investigated in this trilayer. Both non-volatile and volatile skyrmions can be generated by applying a range of voltage sequences. The potential mechanisms, magneto-ionic and electrostatic charge effects, have been discussed as well.</p> <p>Finally, the thickness dependence of Co2MnGa thin films was studied. This material can be used as a spin-orbit generator for manipulating skyrmions. A large anomalous Hall angle (AHA) was demonstrated in Co2MnGa thin films (20 - 50 nm) showing a AHA ~11.4% at low temperature and ~9.7% at room temperature, which can be ascribed to the nontrivial topology of the band structure with large intrinsic Berry curvature. However, the anomalous Hall angle decreases significantly with thicknesses below 20 nm, which band structure calculations confirm is due to the reduction of the majority spin contribution to the Berry curvature.</p>

scholarly journals Skyrmion generation and perpendicular magnetic anisotropy modification in Heusler alloy ultrathin films

2021 ◽  
Author(s):  
◽  
Yao Zhang
Keyword(s):  
Thin Films ◽  
Magnetic Properties ◽  
Band Structure ◽  
Magnetic Anisotropy ◽  
Ultrathin Films ◽  
Heusler Alloy ◽  
Anomalous Hall Effect ◽  
Berry Curvature ◽  
Effective Magnetic Anisotropy ◽  
Hall Angle

<p><b>This thesis explores the magnetic properties of Heusler alloy thin films for spintronics applications. The skyrmion generation under different externalstimulation was focused in MgO/Mn2CoAl/Pd ultrathin films and the anomalous Hall effect of Co2MnGa thin films.</b></p> <p>The perpendicularly magnetized MgO/Mn2CoAl/Pd ultrathin films were firstly optimised by changing the thickness of Pd layer so that the effective magnetic anisotropy can be tuned and various magnetic textures can be obtained for different purposes. Based on the understanding of Pd dependence of magnetic properties, The skyrmion generation by applying an in-plane magnetic field was investigated to fine tune the effective magnetic anisotropy. Further the fractal analysis was used to describe the evolution of the magnetic states and categorise the formation of skyrmions. </p> <p>Then skyrmion generation by ionic liquid gating has been investigated in this trilayer. Both non-volatile and volatile skyrmions can be generated by applying a range of voltage sequences. The potential mechanisms, magneto-ionic and electrostatic charge effects, have been discussed as well.</p> <p>Finally, the thickness dependence of Co2MnGa thin films was studied. This material can be used as a spin-orbit generator for manipulating skyrmions. A large anomalous Hall angle (AHA) was demonstrated in Co2MnGa thin films (20 - 50 nm) showing a AHA ~11.4% at low temperature and ~9.7% at room temperature, which can be ascribed to the nontrivial topology of the band structure with large intrinsic Berry curvature. However, the anomalous Hall angle decreases significantly with thicknesses below 20 nm, which band structure calculations confirm is due to the reduction of the majority spin contribution to the Berry curvature.</p>

scholarly journals Berry curvature origin of the thickness-dependent anomalous Hall effect in a ferromagnetic Weyl semimetal

2021 ◽  
Vol 6 (1) ◽  
Author(s):  
Yao Zhang ◽  
Yuefeng Yin ◽  
Guy Dubuis ◽  
Tane Butler ◽  
Nikhil V. Medhekar ◽  
...  
Keyword(s):  
Band Structure ◽  
Hall Effect ◽  
Room Temperature ◽  
Anomalous Hall Effect ◽  
Berry Curvature ◽  
Weyl Semimetal ◽  
Hall Angle ◽  
20 Nm ◽  
Structure Calculations ◽  
Spin Contribution

AbstractMagnetic Weyl semimetals with spontaneously broken time-reversal symmetry exhibit a large intrinsic anomalous Hall effect originating from the Berry curvature. To employ this large Hall current for room temperature topo-spintronics applications, it is necessary to fabricate these materials as thin or ultrathin films. Here, we experimentally demonstrate that Weyl semimetal Co2MnGa thin films (20–50 nm) show a large anomalous Hall angle ~11.4% at low temperature and ~9.7% at room temperature, which can be ascribed to the non-trivial topology of the band structure with large intrinsic Berry curvature. However, the anomalous Hall angle decreases significantly with thicknesses below 20 nm, which band structure calculations confirm is due to the reduction of the majority spin contribution to the Berry curvature. Our results suggest that Co2MnGa is an excellent material to realize room temperature topo-spintronics applications; however, the significant thickness dependence of the Berry curvature has important implications for thin-film device design.

Effect of Thickness on Mechanically Tunable Magnetic Anisotropy of FeGa Thin Films Deposited on Flexible Substrates

2015 ◽  
Vol 815 ◽  
pp. 227-232 ◽  
Author(s):  
Ying Yu ◽  
Shu Hong Xie ◽  
Qing Feng Zhan
Keyword(s):  
Thin Films ◽  
Magnetic Properties ◽  
Magnetic Anisotropy ◽  
Effective Strain ◽  
Anisotropy Field ◽  
Saturation Field ◽  
Effective Anisotropy ◽  
Magnetostriction Constant ◽  
The Difference ◽  
Different Strains

A practical way to manipulate the magnetic anisotropy of magnetostrictive FeGa thin films grown on flexible polyethylene terephthalate (PET) substrates is introduced in this study. The effect of film thickness on magnetic properties and magnetostriction constant of polycrystalline FeGa thin films was investigated. The anisotropy field Hk of flexible FeGa films, i.e., the saturation field determined by fitting the hysteresis curves measured along the hard axis, was enhanced with increasing the tensile strain applied along the easy axis of the thin films, but this enhancement via strain became unconspicuous with increasing the thickness of FeGa films. In order to study the magnetic sensitivity of thin films responding to the external stress, we applied different strains on these films and measure the corresponding anisotropy field. Moreover, the effective magnetostriction constant of FeGa films was calculated from the changes of both anisotropy field and external strain based on the Villari effect. A Neel’s phenomenological model was developed to illustrate that the effective anisotropy field of FeGa thin films was contributed from both the constant volume term and the inverse thickness dependent surface term. Therefore, the magnetic properties for the volume and surface of FeGa thin films were different, which has been verified in this work by using vibrating sample magnetometer (VSM) and magneto-optic Kerr effect (MOKE) system. The anisotropy field contributed by the surface of FeGa film and obtained by MOKE is smaller than that contributed by the film volume and measured by VSM. We ascribed the difference in Hk to the relaxation of the effective strain applied on the films with increasing the thickness of films.

Exchange Bias in CrO2/Cr2O3 Bilayer Thin Films

2006 ◽  
Vol 45 ◽  
pp. 2528-2533 ◽  
Author(s):  
S. Srinath ◽  
N.A. Frey ◽  
H. Srikanth ◽  
G.X. Miao ◽  
A. Gupta
Keyword(s):  
Thin Films ◽  
Magnetic Anisotropy ◽  
Variable Thickness ◽  
Exchange Bias ◽  
Exchange Coupling ◽  
Hysteresis Loops ◽  
Anisotropy Constant ◽  
Effective Magnetic Anisotropy ◽  
Large Anisotropy

We have investigated the exchange bias in CVD grown epitaxial CrO2/Cr2O3 bilayer thin films using hysteresis loops and resonant RF transverse susceptibility. M-H loops indicated an enhanced coercivity without appreciable loop shift and the transverse susceptibility in CrO2/Cr2O3 bilayers revealed features associated with both the ferromagnetic and antiferromagnetic phases. In addition, TS yielded large anisotropy constant (Keff) values depending on the fraction of Cr2O3 present. The large anisotropy fields observed cannot be accounted for by the variable thickness of CrO2 alone and are indicative of possible exchange coupling between CrO2 and Cr2O3 phases that significantly affects the effective magnetic anisotropy.

scholarly journals Films of rhombohedral graphite as two-dimensional topological semimetals

2019 ◽  
Vol 2 (1) ◽  
Author(s):  
Sergey Slizovskiy ◽  
Edward McCann ◽  
Mikito Koshino ◽  
Vladimir I. Fal’ko
Keyword(s):  
Thin Films ◽  
Anomalous Hall Effect ◽  
Spin Orbit Coupling ◽  
Spin Orbit ◽  
Two Dimensional ◽  
Dimensional Electron ◽  
Berry Curvature ◽  
Electrostatic Gating ◽  
Topological Semimetals ◽  
Intrinsic Magnetic Moment

AbstractTopologically non-trivial states appear in a number of materials ranging from spin-orbit-coupling driven topological insulators to graphene. In multivalley conductors, such as mono- and bilayer graphene, despite a zero total Chern number for the entire Brillouin zone, Berry curvature with different signs concentrated in different valleys can affect the material’s transport characteristics. Here we consider thin films of rhombohedral graphite, which appear to retain truly two-dimensional properties up to tens of layers of thickness and host two-dimensional electron states with a large Berry curvature, accompanied by a giant intrinsic magnetic moment carried by electrons. The size of Berry curvature and magnetization in the vicinity of each valley can be controlled by electrostatic gating leading to a tuneable anomalous Hall effect and a peculiar structure of the two-dimensional Landau level spectrum.

Influence of the Cation on the Surface Electronic Band Structure and Magnetic Properties of Mn:ZnS and Mn:CdS Quantum Dot Thin Films

2019 ◽  
Vol 123 (40) ◽  
pp. 24890-24898 ◽  
Author(s):  
Andrew J. Yost ◽  
Thilini K. Ekanayaka ◽  
Gautam Gurung ◽  
Gaurab Rimal ◽  
Sabit Horoz ◽  
...  
Keyword(s):  
Thin Films ◽  
Magnetic Properties ◽  
Quantum Dot ◽  
Band Structure ◽  
Electronic Band Structure ◽  
Electronic Band

Effect of Stress-induced Magnetic Anisotropy on the Properties of Giant Magnetostrictive Single Layer and Multilayer Thin Films

2004 ◽  
Vol 855 ◽  
Author(s):  
J. H. Tan ◽  
V. H. Guerrero ◽  
R. C. Wetherhold ◽  
W. A. Anderson
Keyword(s):  
Thin Films ◽  
Magnetic Properties ◽  
Magnetic Anisotropy ◽  
Rf Sputtering ◽  
Single Layer ◽  
Annealing Treatment ◽  
Deposition Process ◽  
Vacuum System ◽  
Internal Stresses ◽  
Sensors And Actuators

ABSTRACTGiant magnetostrictive thin films deposited on nonmagnetic substrates can constitute effective sensors and actuators for microdevices. In this work, we investigated the effects of a stress-induced anisotropy on the magnetic properties of Tb0.4Fe0.6, Fe0.5Co0.5 single layer films and [Tb0.4Fe0.6/Fe0.5Co0.5]n multilayers deposited on Si substrates. The magnetostrictive thin films were fabricated by means of RF sputtering and were subjected to a post-deposition annealing treatment. The uniaxial magnetic anisotropy was induced by bending the substrate before deposition and then allowing it to resume its original flat shape after depositing the film. The heat treatment was performed in a vacuum system with a vacuum of 10−6 Torr. The magnetic properties of the fabricated specimens were measured using a SQUID. SEM and XRD analyses were performed to ensure that the thermal treatment would relax the internal stresses induced during the deposition process without crystallizing the film. The thickness of the single layer thin films studied was between 300 and 800 nm while multilayer samples consisted of 6 layers with each layer thickness ranged from about 20 to 40 nm. Compared to single layer samples, multilayer samples with stress anneal growth exhibited an improvement in magnetic saturation by a factor of two while maintaining a low coercive field. Manipulations of the magnitude and direction of magnetic anisotropy was observed by introducing various values of tensile and compressive stress into the film.

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