• JSTS:Journal of Semiconductor Technology and Science
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• v.13 no.6
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• pp.556-561
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• 2013

Interest in spin-torque oscillators (STOs) has been increasing due to their potential use in communication devices. In particular the magnetic tunnel junction-based STO (MTJ-STO) with high perpendicular anisotropy is gaining attention since it can generate high output power. In this paper, a circuit-level model for an in-plane magnetized MTJ-STO with partial perpendicular anisotropy is proposed. The model includes the perpendicular torque and the shift field for more accurate modeling. The bias voltage dependence of perpendicular torque is represented as quadratic. The model is written in Verilog-A, and simulated using HSPICE simulator with a current-mirror circuit and a multi-stage wideband amplifier. The simulation results show the proposed model can accurately replicate the experimental data such that the power increases and the frequency decreases as the value of the perpendicular anisotropy gets close to the value of the demagnetizing field.

• Journal of Magnetics
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• v.18 no.4
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• pp.380-385
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• 2013

We find a metastable vortex state of the perpendicular magnetic anisotropy free layer in spin transfer torque magnetic tunneling junctions by using micromagnetic simulations. The metastable vortex state does not exist in a single layer, and it is only found in the trilayer structure with the perpendicular magnetic anisotropy polarizer layer. It is revealed that the physical origin is the non-uniform stray field from the polarizer layer.

• Journal of the Korean Magnetics Society
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• v.15 no.1
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• pp.25-29
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• 2005

Magnetic properties of YIG films grown by solid phase epitaxy (SPE) was measured as a function of temperature with focus on magneto-crystalline and perpendicular magnetic anisotropy. Perpendicular magnetic anisotropy was not induced in the SPE YIG films annealed at low temperature by relaxing residual stress through formation of dislocation. On the contrary the films annealed at high temperature showed perpendicular magnetic anisotropy which shows very low density of dislocation. Perpendicular magnetic anisotropy field decreased linearly up to a high temperature of $230^{\circ}C$ above which magneto-crystalline anisotropy disappeared. Coercivity also decreased linearly with temperature up 세 $230^{\circ}C$. Magneto-crystalline anisotropy of perpendicular anisotropy induced epitaxial (111) YIG films can be measured using $H_k=4K_1/3M_s$. Temperature behavior of initial susceptibility can be successfully explained by Hopkinson effects. Curie temperature of YIG films grown on GGG substrate with high paramagnetic susceptibility can be easily measured using the results.

• Journal of Magnetics
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• v.14 no.3
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• pp.101-103
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• 2009

The spin transfer torque efficiency was determined experimentally by observing the current-driven domainwall depinning of Pt/CoFe/Pt nanowires with perpendicular magnetic anisotropy. The depinning time was exponentially proportional to the applied magnetic field, and was well explained by the Neel-Brown formula. The depinning time and threshold magnetic field were varied considerably by injecting current into the nanowire. The spin transfer torque efficiency was estimated to be $(7.2{\pm}0.9){\times}10^{-15}Tm^2$/A from the linear dependence of the threshold current density with respect to the applied magnetic field.

• Journal of Magnetics
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• v.18 no.1
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• pp.5-8
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• 2013

The perpendicular magnetic anisotropy of sputtered CoFeB thin films covered by MgO was investigated by vibrating sample magnetometry. Three different $Co_xFe_{80-x}B_{20}$ alloys were studied. Under out-of plane magnetic field, the saturation field was found to increase with increasing the Co content. The magnetization and interface anisotropy energy were obtained for all samples. Both showed a marked dependence on the MgO overlayer thickness. In addition, their variations were found to be non-monotonous as a function of the Co concentration.

• Journal of Magnetics
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• v.20 no.1
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• pp.8-10
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• 2015

The magnetic anisotropy field plays an important role in spin-orbit-torque-induced magnetization dynamics with electric current injection. Here, we propose a magnetometric technique to measure the magnetic anisotropy field in nanostructured ferromagnetic thin films. This technique utilizes a magneto-optical Kerr effect microscope equipped with two-axis electromagnets. By measuring the out-of-plane hysteresis loops and then analyzing their saturated magnetization with respect to the in-plane magnetic field, the magnetic anisotropy field is uniquely quantified within the context of the Stoner-Wohlfarth theory. The present technique can be applied to small nanostructures, enabling in-situ determination of the magnetic anisotropy field of nanodevices.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.17 no.8
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• pp.888-892
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• 2004

It is necessary to develop soft magnetic layer with high saturation magnetization 4 $\pi{M}_s$ and in-plane magnetic anisotropy field Hk for soft magnetic underlayer of perpendicular magnetic recording media with high signal to noise ratio. Fe-Co-B layer with high 4 $\pi$Ms of about 23 kG deposited on Ni-Fe and Ni-Fe/Si seedlayer exhibited very high in-plane magnetic anisotropy filed Hk of about 280 and 380 Oe, respectively, In-plane XRD studies clarified that the lattice spacing of planes along the easy axis direction was longer than that along the hard axis direction in the Fe-Co-B layers with high Hk. These results indicate that high Hk of Fe-Co-B/Ni-Fe and Fe-Co-B/［Ni-Fe/si］ layers were resulted from magnetoelastic anisotropy owing to a residual stress. Moreover, the high Hk in the Fe-Co-B/Ni-Fe layer was maintained until 30$0^{\circ}C$ annealing temperature.

• Journal of Magnetics
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• v.10 no.1
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• pp.33-35
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• 2005

Perpendicular magnetization curves and crystal textures of $[Pd(0.8 nm)/Co(0.8 nm)]_5/FeMn$ multilayers having an exchange-biased perpendicular magnetic anisotropy as a function of FeMn thickness and annealing temperature were measured. As FeMn thickness increases from 0 to 21 nm, the perpendicular exchange biasing field ($H_{ex}$) obtained the maximum value of 130 Oe at FeMn thickness 12 nm. As the annealing temperature increases to $240^{\circ}C$, the H_ex increased from 115 Oe to 190 Oe and the exchange-biased perpendicular magnetic anisotropy disappeared at $330^{\circ}C$.

• Current Applied Physics
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• v.18 no.11
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• pp.1212-1217
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• 2018

The electric field-induced modifications of magnetic anisotropy in CoFeB/MgO systems are studied using X-ray resonant magnetic scattering and magneto-optical Kerr effect. Voltage dependent changes of the magnetic anisotropy of -12.7 fJ/Vm and -8.32 fJ/Vm are observed for Ta/CoFeB/MgO and Hf/CoFeB/MgO systems, respectively. This implies that the interfacial perpendicular magnetic anisotropy is reduced (enhanced) when electron density is increased (decreased). X-ray resonant magnetic scattering measurements reveal that the small in-plane magnetic component of the remanent state of CoFeB/MgO systems with weak magnetic anisotropy changes depending on the applied voltage leading to modification of the magnetic anisotropy at the CoFeB/MgO interface.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2000.11a
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• pp.492-495
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• 2000

In order to develop an ultra-thin CoCr perpendicular magnetic recording layer, we prepared CoCrTa/Ti double layer for perpendicular magnetic recording media by new facing targets sputtering system, Crystallgraphics and magnetic characteristics of CoCrTa on underlayer substrate temperature have been investigated. Crystallgraphic and magnetic characteristic of thin films were evaluated by X-ray diffractometry(XRD), vibrating sample magnetometer(VSM) and atomic force microscopy(AFM). The coercivity and anisotropy field was increased by increasing under layer substrate temperature, c-axis orientation of CoCrTa magnetic recording layer was improved 8$^{\circ}$ to 5.6$^{\circ}$when under layer substrate temperature was 250[$^{\circ}C$]. Also, through annealing effect for CoCrTa/Ti double layer, it was certain that crystallgraphics and magnetic characteristics was improved.