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Local Variation of Magnetic Parameters of the Free Layer in TMR Junctions
CheolGi Kim,Toshihiro Shoyama,Masakiyo Tsunoda,Migaku Takahashi,Tae Hyo Lee,Chong-Oh Kim 한국자기학회 2002 Journal of Magnetics Vol.7 No.3
Local M-H loops have been measured on the free layer of a tunneling magnetoresistance (TMR) junction using the magneto-optical Kerr effect (MOKE) system, with an optical beam size of about 2 ㎛ diameter. Tunnel junctions were deposited using the DC magnetron sputtering method in a chamber with a base pressure of 3 × 10^(-9) Torr. The relatively irregular variations of coercive force Hc (~17.5 Oe) and unidirectional anisotropy field Hua (~7.5 Oe) in the as-deposited sample are revealed. After 200 ℃ annealing, Hc decreases to 15 Oe but Hua increases to 20 Oe with smooth local variations. Two-dimensional plots of Hc and Hua show the symmetric saddle shapes with their axes aligned with the pinned layer, irrespective of the annealing field angle. This is thought to be caused by geometric effects during deposition, together with a minor annealing effect. In addition, the variation of root mean square (RMS) surface roughness reveals it to be symmetric with respect to the center of the pinned-layer axis, with the roughness of 2.5 Å near the edge and 5.8 Å at the junction center. Comparison of surface roughness with the variation of Hua suggests that the Hua variation of the free layer is well described by dipole interactions related to surface roughness. As a whole, the reversal magnetization is not uniform over the entire junction area and the macroscopic properties are governed by the average sum of local distributions.
Single Magnetic Bead Detection in a Microfluidic Chip Using Planar Hall Effect Sensor
Hyuntai Kim,Venu Reddy,Kun Woo Kim,Ilgyo Jeong,Xing Hao Hu,CheolGi Kim 한국자기학회 2014 Journal of Magnetics Vol.19 No.1
In this study, we fabricate an integrated microfluidic chip with a planar Hall effect (PHE) sensor for single magnetic bead detection. The PHE sensor was constructed with a junction size of 10 μm × 10 μm using a trilayer structure of Ta(3 nm)/NiFe(10 nm)/Cu(1.2 nm)/IrMn(10 nm)/Ta(3 nm). The sensitivity of the PHE sensor was 19.86 μV/Oe. A diameter of 8.18 μm magnetic beads was used, of which the saturation magnetization was ~2.1 emu/g. The magnetic susceptibility χ of these magnetic beads was calculated to be~0.14. The diluted magnetic beads solution was introduced to the microfluidic channel attributing a single bead flow and simultaneously the PHE sensor voltage was measured to be 0.35 μV. The integrated microchip was able to detect a magnetic moment of 1.98 × 10<SUP>?10</SUP> emu.
Sarah Kim,Jun-Ho Jeong,Sung-Chul Shin,Vo Thanh Son,Bo-Geon Jeon,CheolGi Kim,Jong-Ryul Jeong 한국자기학회 2010 Journal of Magnetics Vol.15 No.1
Combined study of in-situ stress measurements and atomic force microscopy (AFM) revealed drastic stress relaxation in the CoCrPt and PS(styrene)-PVP(vinyl pyridine) polymer hybrid structure that was closely related to the growth structure of the film. We have observed not only no large initial growth stress at the initial stages of film growth but also twice smaller stress in magnitude with opposite sign in the CoCrPt/PS-PVP/Si sample. The microstructural studies using AFM at the various film growth stages revealed that the film growth structure plays an important role in the stress relaxation mechanism of CoCrPt films on a corrugated polymer surface.