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You, Chun-Yeol,Kim, Hyungsuk IEEE 2017 IEEE transactions on magnetics Vol.53 No.11
<P>We investigate the effect of tunneling magnetoresistance (TMR) on the spin transfer-torque (STT) switching behaviors in magnetic tunneling junctions. In most of the micromagnetic simulations for STT switching, a uniform current density has been assumed, which is not realistic in the high TMR devices. The local STT is proportional to the local current density, and the local current density will be determined by the local resistivity. Since higher than 150% of TMR values is required in the real STT-magnetoresistive random access memory devices, the local resistance is dramatically changed as a function of the relative spin orientation between the fixed and free layers under the constant voltage operation mode. By employing non-uniform current density in STT switching simulations using the 'embedded object-oriented micromagnetic framework' scheme, we found that the details of switching behaviors such as switching time and critical current density are significantly influenced by the TMR values.</P>
Dependence of the switching current density on the junction sizes in spin transfer torque
You, Chun-Yeol,Jung, Myung-Hwa American Institute of Physics 2013 JOURNAL OF APPLIED PHYSICS - Vol.113 No.7
<P>We investigate the dependence of switching current density on the junction sizes in the in-plane spin transfer torque nanopillar structures by using micromagnetic simulations. While the macrospin model predicts weak dependence of switching current density on the junction sizes, we find that the switching current density is a sensitive function of the junction sizes. It can be explained with the complicated spin configurations and dynamics during the switching process. The detail spin configurations and dynamics are determined by spin wave excitation with the finite wave vector, which is related with the exchange coupling energy and junction shape. (C) 2013 American Institute of Physics. [http://dx.doi.org/10.1063/1.4792728]</P>
Micromagnetic Simulations for Spin Transfer Torque in Magnetic Multilayers
Chun-Yeol You 한국자기학회 2012 Journal of Magnetics Vol.17 No.2
We investigate spin transfer torque (STT) in magnetic multilayer structures using micromagnetic simulations. We implement the STT contribution for magnetic multilayer structures in addition to the Landau-Lifshitz-Gilbert (LLG) micromagnetic simulators. In addition to the Sloncewski STT term, the zero, first, and second order field-like terms are also considered as well as the effects of the Oersted field due to the running current are addressed. We determine the switching current densities of the free layer with the exchange biased synthetic ferrimagnetic reference layers for various cases.
Spin Torque Nano-Oscillator with an Exchange-Biased Free Rotating Layer
Chun-Yeol You 한국자기학회 2009 Journal of Magnetics Vol.14 No.4
We propose a new type of spin torque nano-oscillator structure with an exchange- biased free rotating layer. The proposed spin torque nano-oscillator consists of a fixed layer and a free rotating layer with an additional anti-ferromagnetic layer, which leads to an exchange bias in the free rotating layer. The spin dynamics of the exchange-biased free rotating layer can be described as an additional exchange field because the exchange bias manifests itself by the existance of a finite exchange bias field. The exchange bias field plays a similar role to that of a finite external field. Hence, microwave generation can be achieved without an external field in the proposed structure.
Formation of a Narrow Domain Wall by Using a Local Interlayer Exchange Coupled System
Chun-Yeol You 한국물리학회 2005 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.47 No.2
Formation of a narrow magnetic domain wall is demonstrated by using micromagnetic simulations. It is found that the domain wall width can be shrunk in a local interlayer exchange coupled system. A local interlayer exchange coupled system means that only part of a ferromagnetic layer has an nterlayer exchange coupling with another rromagnetic layer. The system can be considered as two parts with respect to the lateral dimensions: one is an exchange coupled region, and the another is a free region. Since the two regions have quite different local switching fields, the domain wall will be formed at the interface between the two regions at moderate fields. Furthermore, the transport between the two domains might be more ballistic, so a larger domain wall magnetoresistance would be expected.