scholarly journals Rare earth nitrides and their applications in magnetic tunnel junctions

2021 ◽  
Author(s):  
◽  
Felicia Ullstad
Keyword(s):  
Rare Earth ◽  
Room Temperature ◽  
Tunnel Junctions ◽  
Magnetic Tunnel Junctions ◽  
Tunnel Barrier ◽  
Minimum Thickness ◽  
Rare Earth Nitrides ◽  
Wide Range ◽  
Linear Behaviour ◽  
The Rare Earth

<p>In this thesis, we investigate the rare earth nitrides, a family of materials containing many intrinsic ferromagnetic semiconductors, with a particular focus on GdN and SmN.We investigate the rare earth nitride formation reaction, explore some properties of GdN and SmN, and finally manufacture and measure magnetic tunnel junctions which incorporate rare earth nitrides. The investigations of the reaction and properties of the materials are used to improve and understand the magnetic tunnel junctions. All samples and devices are grown at room temperature, giving polycrystalline rare earth nitride films.  We show that a rare earth surface can catalytically break theN2 molecule at ambient temperature and low pressures. We follow the nitrogen reacting with the rare earth to form a rare earth nitride in real time via conductance measurements. By comparing the N2 cracking, reaction, and diffusion at both a RE and a REN surface we propose a pressure range in which the nitrogen content in SmN can be manipulated and conclude that the nitrogen in the top monolayers in a SmN film is mobile.  In the investigation of GdN and SmN, we find that the conductivity of SmN follows the same behaviour as GdN when changing the N2 pressure during deposition. We follow the conductance change in SmN during deposition and propose a minimum thickness for room temperature deposited SmN films for consistent conductivity measurements. We report structural and magnetic changes in GdN which has been exposed to N-ions. We also present data on materials making ohmic contact to both GdN and SmN.  Finally, we report the manufacturing and investigation of magnetic tunnel junctions using GdN and SmN electrodes with a GaN tunnel barrier. A new pattern design produces 20 devices, in a single deposition, which show consistent behaviour and expands on previous work on this topic. The main focus of the investigation is the J-V characteristics of the magnetic tunnel junctions which shows clear non-linear behaviour arising from tunnelling through the GaN. A Simmons fit to the J-V characteristics yields a barrier height of 0:8 eV and barrier thicknesses close to experimentally determined thicknesses. The J-V characteristics are investigated with changing temperature and changing applied magnetic field to investigate the effect of the ferromagnetism of the GdN and SmN electrodes. The tunnel magnetoresistance (TMR) of the devices show two contributions, a low-temperature TMR contribution and a 50K TMR contribution, and the maximum TMR for all devices are between 100% to 600%. The devices can withstand current densities up to 4000A/cm² and voltages up to 5V which is promising for a wide range of future applications.</p>

scholarly journals Rare earth nitrides and their applications in magnetic tunnel junctions

2021 ◽  
Author(s):  
◽  
Felicia Ullstad
Keyword(s):  
Rare Earth ◽  
Room Temperature ◽  
Tunnel Junctions ◽  
Magnetic Tunnel Junctions ◽  
Tunnel Barrier ◽  
Minimum Thickness ◽  
Rare Earth Nitrides ◽  
Wide Range ◽  
Linear Behaviour ◽  
The Rare Earth

<p>In this thesis, we investigate the rare earth nitrides, a family of materials containing many intrinsic ferromagnetic semiconductors, with a particular focus on GdN and SmN.We investigate the rare earth nitride formation reaction, explore some properties of GdN and SmN, and finally manufacture and measure magnetic tunnel junctions which incorporate rare earth nitrides. The investigations of the reaction and properties of the materials are used to improve and understand the magnetic tunnel junctions. All samples and devices are grown at room temperature, giving polycrystalline rare earth nitride films.  We show that a rare earth surface can catalytically break theN2 molecule at ambient temperature and low pressures. We follow the nitrogen reacting with the rare earth to form a rare earth nitride in real time via conductance measurements. By comparing the N2 cracking, reaction, and diffusion at both a RE and a REN surface we propose a pressure range in which the nitrogen content in SmN can be manipulated and conclude that the nitrogen in the top monolayers in a SmN film is mobile.  In the investigation of GdN and SmN, we find that the conductivity of SmN follows the same behaviour as GdN when changing the N2 pressure during deposition. We follow the conductance change in SmN during deposition and propose a minimum thickness for room temperature deposited SmN films for consistent conductivity measurements. We report structural and magnetic changes in GdN which has been exposed to N-ions. We also present data on materials making ohmic contact to both GdN and SmN.  Finally, we report the manufacturing and investigation of magnetic tunnel junctions using GdN and SmN electrodes with a GaN tunnel barrier. A new pattern design produces 20 devices, in a single deposition, which show consistent behaviour and expands on previous work on this topic. The main focus of the investigation is the J-V characteristics of the magnetic tunnel junctions which shows clear non-linear behaviour arising from tunnelling through the GaN. A Simmons fit to the J-V characteristics yields a barrier height of 0:8 eV and barrier thicknesses close to experimentally determined thicknesses. The J-V characteristics are investigated with changing temperature and changing applied magnetic field to investigate the effect of the ferromagnetism of the GdN and SmN electrodes. The tunnel magnetoresistance (TMR) of the devices show two contributions, a low-temperature TMR contribution and a 50K TMR contribution, and the maximum TMR for all devices are between 100% to 600%. The devices can withstand current densities up to 4000A/cm² and voltages up to 5V which is promising for a wide range of future applications.</p>

scholarly journals Electronic Structure of the Rare-Earth Nitrides

2021 ◽  
Author(s):  
◽  
A. R. H. Preston
Keyword(s):  
Electronic Structure ◽  
Rare Earth ◽  
Band Structure ◽  
Electronic Band Structure ◽  
Electronic Band ◽  
X Ray ◽  
Rare Earth Nitrides ◽  
Wide Range ◽  
X Ray Absorption ◽  
The Rare Earth

<p>The rare-earth nitrides (ReNs) are a class of novel materials with potential for use in spintronics applications. Theoretical studies indicate that among the ReNs there could be half-metals, semimetals and semiconductors, all exhibiting strong magnetic ordering. This is because of the complex interaction between the partially filled rare-earth 4f orbital and the nitrogen 2p valence and rare-earth 5d conduction bands. This thesis uses experimental and theoretical techniques to probe the ReN electronic structure. Thin films of SmN, EuN, GdN, DyN, LuN and HfN have been produced for study. Basic characterization shows that the films are of a high quality. The result of electrical transport, magnetometry, and optical and x-ray spectroscopy are interpreted to provide information on the electronic structure. SmN, GdN, DyN are found to be semiconductors in their ferromagnetic ground state while HfN is a metal. Results are compared with density functional theory (DFT) based calculations. The free parameters resulting from use of the local spin density approximation with Hubbard-U corrections as the exchange-correlation functional are adjusted to reach good agreement with x-ray absorption and emission spectroscopy at the nitrogen K-edge. Resonant x-ray emission is used to experimentally measure valence band dispersion of GdN. No evidence of the rare-earth 4f levels is found in any of the K-edge spectroscopy, which is consistent with the result of M-edge x-ray absorption which show that the 4f wave function of the rare-earths in the ReNs are very similar to those of rare-earth metal. An auxillary resonant x-ray emission study of ZnO is used to map the dispersion of the electronic band structure across a wide range of the Brillouin zone. The data, and calculations based on GW corrections to DFT, together provide a detailed picture of the bulk electronic band structure.</p>

Spin-Polarized Current in Spin Valves and Magnetic Tunnel Junctions

MRS Bulletin ◽  
2006 ◽  
Vol 31 (5) ◽  
pp. 389-394 ◽  
Author(s):  
Stuart Parkin
Keyword(s):  
Room Temperature ◽  
Tunnel Junctions ◽  
Magnetic Tunnel Junctions ◽  
Memory Storage ◽  
Tunnel Barrier ◽  
Tunnel Magnetoresistance ◽  
Ferromagnetic Electrodes ◽  
Diffusive Scattering ◽  
Spin Polarized ◽  
Tunnel Barriers

AbstractSpin-polarized currents can be generated by spin-dependent diffusive scattering in magnetic thin-film structures or by spin-dependent tunneling across ultrathin dielectrics sandwiched between magnetic electrodes.By manipulating the magnetic moments of the magnetic components of these spintronic materials, their resistance can be significantly changed, allowing the development of highly sensitive magnetic-field detectors or advanced magnetic memory storage elements.Whereas the magneto-resistance of useful devices based on spin-dependent diffusive scattering has hardly changed since its discovery nearly two decades ago, in the past five years there has been a remarkably rapid development in both the basic understanding of spin-dependent tunneling and the magnitude of useful tunnel magnetoresistance values.In particular, it is now evident that the magnitude of the spin polarization of tunneling currents in magnetic tunnel junctions not only is related to the spin-dependent electronic structure of the ferromagnetic electrodes but also is considerably influenced by the properties of the tunnel barrier and its interfaces with the magnetic electrodes.Whereas the maximum tunnel magnetoresistance of devices using amorphous alumina tunnel barriers and 3d transition-metal alloy ferromagnetic electrodes is about 70% at room temperature, using crystalline MgO tunnel barriers in otherwise the same structures gives tunnel magnetoresistance values of more than 350% at room temperature.

scholarly journals Electronic Structure of the Rare-Earth Nitrides

2021 ◽  
Author(s):  
◽  
A. R. H. Preston
Keyword(s):  
Electronic Structure ◽  
Rare Earth ◽  
Band Structure ◽  
Electronic Band Structure ◽  
Electronic Band ◽  
X Ray ◽  
Rare Earth Nitrides ◽  
Wide Range ◽  
X Ray Absorption ◽  
The Rare Earth

<p>The rare-earth nitrides (ReNs) are a class of novel materials with potential for use in spintronics applications. Theoretical studies indicate that among the ReNs there could be half-metals, semimetals and semiconductors, all exhibiting strong magnetic ordering. This is because of the complex interaction between the partially filled rare-earth 4f orbital and the nitrogen 2p valence and rare-earth 5d conduction bands. This thesis uses experimental and theoretical techniques to probe the ReN electronic structure. Thin films of SmN, EuN, GdN, DyN, LuN and HfN have been produced for study. Basic characterization shows that the films are of a high quality. The result of electrical transport, magnetometry, and optical and x-ray spectroscopy are interpreted to provide information on the electronic structure. SmN, GdN, DyN are found to be semiconductors in their ferromagnetic ground state while HfN is a metal. Results are compared with density functional theory (DFT) based calculations. The free parameters resulting from use of the local spin density approximation with Hubbard-U corrections as the exchange-correlation functional are adjusted to reach good agreement with x-ray absorption and emission spectroscopy at the nitrogen K-edge. Resonant x-ray emission is used to experimentally measure valence band dispersion of GdN. No evidence of the rare-earth 4f levels is found in any of the K-edge spectroscopy, which is consistent with the result of M-edge x-ray absorption which show that the 4f wave function of the rare-earths in the ReNs are very similar to those of rare-earth metal. An auxillary resonant x-ray emission study of ZnO is used to map the dispersion of the electronic band structure across a wide range of the Brillouin zone. The data, and calculations based on GW corrections to DFT, together provide a detailed picture of the bulk electronic band structure.</p>

scholarly journals Exceeding 400% tunnel magnetoresistance at room temperature in epitaxial Fe/MgO/Fe(001) spin-valve-type magnetic tunnel junctions

2021 ◽  
Vol 118 (4) ◽  
pp. 042411
Author(s):  
Thomas Scheike ◽  
Qingyi Xiang ◽  
Zhenchao Wen ◽  
Hiroaki Sukegawa ◽  
Tadakatsu Ohkubo ◽  
...  
Keyword(s):  
Room Temperature ◽  
Tunnel Junctions ◽  
Spin Valve ◽  
Magnetic Tunnel Junctions ◽  
Tunnel Magnetoresistance

Fabrication of fully epitaxial magnetic tunnel junctions with a Co2MnSi thin film and a MgO tunnel barrier

2007 ◽  
Vol 310 (2) ◽  
pp. 2006-2008 ◽  
Author(s):  
H. Kijima ◽  
T. Ishikawa ◽  
T. Marukame ◽  
K.-I. Matsuda ◽  
T. Uemura ◽  
...  
Keyword(s):  
Thin Film ◽  
Tunnel Junctions ◽  
Magnetic Tunnel Junctions ◽  
Tunnel Barrier

Influence of the Annealing Ambient on Structural and Optical Properties of Rare Earth Implanted GaN

2005 ◽  
Vol 892 ◽  
Author(s):  
Katharina Lorenz ◽  
E. Nogales ◽  
R. Nédélec ◽  
J. Penner ◽  
R. Vianden ◽  
...  
Keyword(s):  
Optical Properties ◽  
Rare Earth ◽  
Room Temperature ◽  
Rutherford Backscattering Spectrometry ◽  
Strong Increase ◽  
Structural And Optical Properties ◽  
Nitrogen Gas ◽  
Higher Temperature ◽  
The Eu ◽  
The Rare Earth

AbstractGaN films were implanted with Er and Eu ions and rapid thermal annealing was performed at 1000, 1100 and 1200 °C in vacuum, in flowing nitrogen gas or a mixture of NH3 and N2. Rutherford backscattering spectrometry in the channeling mode was used to study the evolution of damage introduction and recovery in the Ga sublattice and to monitor the rare earth profiles after annealing. The surface morphology of the samples was analyzed by scanning electron microscopy and the optical properties by room temperature cathodoluminescence (CL). Samples annealed in vacuum and N2 already show the first signs of surface dissociation at 1000 °C. At higher temperature, Ga droplets form at the surface. However, samples annealed in NH3 + N2 exhibit a very good recovery of the lattice along with a smooth surface. These samples also show the strongest CL intensity for the rare earth related emissions in the green (for Er) and red (for Eu). After annealing at 1200 °C in NH3+N2 the Eu implanted sample reveals the channeling qualities of an unimplanted sample and a strong increase of CL intensity is observed.

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