• Journal of Magnetics
• /
• 제17권3호
• /
• pp.168-171
• /
• 2012

Irreversible magnetization between the zero-field-cooled (ZFC) and field-cooled (FC) states in $Y_{1-x}Sr_xMnO_3$ (x=0 and 0.2) was investigated. $YMnO_3$ and $Y_{0.8}Sr_{0.2}MnO_3$ have a hexagonal structure and the lattice parameter a decreases from 7.4408 ${\AA}$ to 7.4327 ${\AA}$ while c increases from 12.2244 ${\AA}$ to 12.2287 ${\AA}$ for $YMnO_3$ and $Y_{0.8}Sr_{0.2}MnO_3$, respectively. An anomaly is observed at around 74 K in ZFC and FC magnetization measurements for $YMnO_3$, whereas in $Y_{0.8}Sr_{0.2}MnO_3$ the ${\sigma}_{ZFC}$ and ${\sigma}_{FC}$ are split at low temperature, indicating glass-like behavior.

• Journal of Magnetics
• /
• 제6권4호
• /
• pp.132-141
• /
• 2001

The switching characteristics and the magnetization-flop behavior in magnetic tunnel junctions exchange biased by synthetic antiferromagnets (SyAFs) are investigated by using a computer simulations based on a single-domain multilayer model. The bias field acting on the free layer is found to be sensitive to the thickness of neighboring layers, and the thickness dependence of the bias field is greater at smaller cell dimensions due to larger magnetostatic interactions. The resistance to magnetization flop increases with decreasing cell size due to increased shape anisotropy. When the cell dimensions are small and the synthetic antiferromagnet is weakly, or not pinned, the magnetization directions of the two layers sandwiching the insulating layer are aligned antiparallel due to a strong magnetostatic interaction, resulting in an abnormal magneto resistance (MR) change from the high-MR state to zero, irrespective of the direction of the free-layer switching. The threshold field for magnetization-flop is found to increase linearly with increasing antiferromagnetic exchange coupling in the synthetic antiferromagnet. Irrespective of the magnetic parameters and cell sizes, magnetization flop does not exist near zero applied field, indicating that magnetization flop is driven by the Zeeman energy.

• Journal of Magnetics
• /
• 제21권4호
• /
• pp.622-628
• /
• 2016

Magnetization property is a critical factor for magnetorheological fluids (MRFs) to achieve the liquid-solid transition. The main focus of this study is on exploring the influence factors on magnetization properties of MRFs. In this paper, a theoretical analysis is performed to discuss the magnetization characteristics of MRFs firstly. Then, a method for the preparation of carbonyl iron-based MRFs is illustrated and five MRFs samples with various material parameters are prepared. It is succeeded by a series of experiments on testing the hysteresis loop and the magnetization curve of each sample and the influence factors are compared and analyzed. Experimental results indicate that there is basically no hysteresis phenomenon on MRFs which exhibits superparamagnetic behavior at room temperature. A surfactant coating on magnetic particles can slightly improve the MRFs magnetization. Additionally, the magnetic susceptibility and the saturation magnetization both increase with the particle concentration, whereas the influence of particle diameter is relatively very small. Moreover, as the temperature increases, the magnetization decreases and the declining rate accelerates gradually.

• 한국세라믹학회지
• /
• 제39권1호
• /
• pp.12-15
• /
• 2002

Ultrafine cadmium ferrite particles have been investigated by X-ray diffractometry, transmission electron microscopy and SQUID magnetometry. All peaks of X-ray diffraction patterns are broad, but correspond to a cubic spinel structure with the lattice constant of 8.65 $\AA$. The average particle size determined by TEM is 9.7 nm and the size distribution of particles is not normal, but lognormal. The maximal magnetization measured at 5 K was 17.7 emu/g. The experimental data show a transi-tion from a disorder ferrimagnetic phase to a spin-glass phase (i.e. reentrant behavior) with a freezing temperature (T$\_$f/) of 30 K. Superparamagnetic behavior of the particles is confirmed by the coincidence of the plots of M vs. H/T for 100 and 300 K.

• 한국초전도ㆍ저온공학회논문지
• /
• 제7권4호
• /
• pp.10-13
• /
• 2005

Transport current and magnetic field which is generated by transport current make AC current - AC mag-netic field condition(AC-AC condition) in AC power application system using HTS tape. Therefore, characteristics of AC loss under the AC-AC condition are necessary to estimate AC loss of power device with accuracy such as HTS transformer. In this paper, we researched transport current loss, magnetization loss by perpendicular magnetic field and total loss which is represented as summation of both losses under the AC-AC condition in single HTS tape. As a result, magnetization loss showed increasing behavior under 65mT and decreasing behavior upper 65mT by influence of transport current. Transport current loss was increased continuously through out whole measurement ranges in the AC-AC condition. Total loss in HTS tape was dominated entirely by magnetization loss.

• 한국자기학회:학술대회 개요집
• /
• 한국자기학회 2011년도 임시총회 및 하계학술연구발표회
• /
• pp.3-3
• /
• 2011

Since the first discovery of exchange anisotropy on Co/CoO system[1], there have been numerous studies to explore the physical origin of exchange-biased system[2,3]. In this presentation, we report that how the polarized neutron reflectomery can be applied to study the magnetization reversal behavior of the exchange biased system. As an example, the detailed magnetization reversal mechanism of the exchange-biased Py(30 nm)/FeMn (0, 15, 30 nm)/CoFe(30 nm) trilayers was studied and found that the 15 nm antiferromagnetic FeMn layer mediates the magnetization reversal behaviors of both Py and CoFe layers through interlayer exchange bias coupling. We also update the current activities in polarized neutron reflectometer in HANARO.

• 한국자기학회지
• /
• 제6권4호
• /
• pp.199-203
• /
• 1996

Co/Pd 다층박막의 자화반전 거동을 조사하기 위하여, 먼저 시료를 자기장 소거법으로 탈자시킨 다음 초기자화 곡선과 minor loops 를 측정하였다. 또한 보자력 및 포화자화는 수직자화곡선으로부터 구하였으며, 수직자기이방성은 온도별로 측정한 수직 및 수평자화곡선의 면적차이를 이용하여 구하였다. 자화반저거동의 분석을 위하여 여러가지 정상적이고 반정량적인 방법을 측정결과에 적용하였다. 이들 결과로부터 본 실험에 사용된 시료의 자화반전의 지배적인 거동은 자벽의 pinning이며, 스퍼터링 압력이 증가할수록 보자력이 증가하는 경향은 Kronmuller 식 $H_{c}$ (T) .var. $r_{o}$ .center dot. $K_{u}$에 의해 설명될 수 있었다.다.다.

• 한국자기학회:학술대회 개요집
• /
• 한국자기학회 2013년도 임시총회 및 하계학술연구발표회
• /
• pp.15-16
• /
• 2013

Magnetization behavior of ultra thin $Fe_xCo_{1-x}$ alloy (where x varies from 0 to 100) has been investigated as functions of composition on Cr (100) substrate by using in situ surface magneto optical Kerr effect (SMOKE). It's always show in plane uniaxial magnetic anisotropy at room temperature (RT) & Low temperature (LT). It is observed that composition dependent coercive force maximum at about 30 at % Co and 70 at % Co atomic ratio and minimum near equiatomic site. The relative magnetic moments as composition variation also show magnetization collapse near equiatomic site. The magnetization behaviors of Fe-Co alloy on Cr (100) due to composition varies are supported the order-disordering as well as structural stability bcc (ferromagnetic)/fcc (anti-ferromagnetic) phase stability magnetism.

• 한국표면공학회지
• /
• 제32권1호
• /
• pp.61-66
• /
• 1999

The Spin-dependent tunneling magnetoresistance (TMR) effect was observed in $NiFe/Al_2O_3$/Co thin films. The samples were prepared by magnetron sputtering in a system with a base pressure of $3\times10^{-6}$Torr. the insulating $Al_2O_3$layer was prepared by r.f. plasma oxydation method of a metallic Al layer. The ferromagnetic and insulating layers were deposited through metallic masks to produce the cross pattern form. The junction has an active area of $0.3\times0.3\textrm{mm}^2$ and the $Al_2O_3$layer is deposited through a circular mask with a diameter of 1mm. It is very important that insulating layer is formed very thinly and uniformly in tunneling junction. The ferromagnetic layer was fabricated in optimum conditions and the surface of that was very flat, which was observed by AFM. Tunneling junction was confirmed through nonlinear I-V curve. $NiFe/Al_2O_3$/Co junction was observed for magnetization behavior and magnetoresistance property and magnetoresistance property is dependent on magnetization behavior and magnetoresistance property and magnetoresistance property is dependent on magnetization behavior of t재 ferromagnetic layer. The maximum magnetoresistance ratio was about 6.5%.

• 한국자기학회:학술대회 개요집
• /
• 한국자기학회 2000년도 International Symposium on Magnetics The 2000 Fall Conference
• /
• pp.279-286
• /
• 2000

Magnetic field dependence of magnetization reversal in Co/Pt multilayers has been quantitatively investigated. Serial samples of Co/Pt multilayers have been prepared by dc-magnetron sputtering under various Ar pressure. Magnetization reversal was monitored by magnetization viscosity measurement and direct domain observation using a magneto-optical microscope system, and the wall-motion speed and the nucleation rate R were determined using a domain reversal model based on time-resolved domain reversal patterns. Both and R were found to be exponentially dependent on the reversing applied field. From the exponential dependencies, the activation volumes of the wall motion and nucleation could be determined based on a thermally activated relaxation model, and the wall-motion activation volume was revealed to be slightly larger than the nucleation activation volume.