Hydrogenation induced reversible long-range magnetic ordering in CoPd alloy thin films

• Main Authors: Huang, Han-Yuan, 黃瀚元
• Other Authors: Lin, Wen-Chin
• Format: Others
• Language: en_US
• Published: 2015
• Online Access: http://ndltd.ncl.edu.tw/handle/41433412563626865338

碩士 === 國立臺灣師範大學 === 物理學系 === 103 === The hydrogenation effect on the various thickness Co_(1-x) Pd_x/Al_2 O_3 (0001) films investigated the magnetic and reversible properties. The concentration of Co and Pd was determined by Auger electron spectrum. The magnetic properties were measured using Magneto-Optical Kerr Effect (MOKE) and Superconducting Quantum Interference Device Vibrating Sample Magnetometer (SQUID). The morphology was measured using AFM ex-situ. Palladium were transferred into Palladium hydride (PdH_x) and the lattice constant was expanded during hydrogen adsorption and absorption process. The hydrogenation effect were unobvious in Co-rich (Co_67 Pd_33) sample. When the concentration of Pd was increased to 86 %, the magnetic coercivity was enhanced 10 times. Moreover, the squareness of hysteresis loop was also enhanced from 10 % to 100 % after exposed 40 mbar of hydrogen gas within 2-3 sec. This behavior might cause from dilute magnetic material with long-range magnetic ordering. Besides, the efficiency of hydrogenation effect was influenced by different thickness of Co_39 Pd_61 alloy. After removed the hydrogen atoms by mechanical pump, the shape of hysteresis loops returned from β-phase to α-phas during 2-3 sec. This behavior means that the hydrogenation process in palladium is reversible. Atomic force microscopy (AFM) figure shows the Co_0.14 Pd_0.86 alloy’s morphology, which has many 100 nm diameter nano-clusters and mounts of 20 nm nano-dots at nearby clusters can not only enhance the interaction surface but also create the different surface cross section. Both of properties can improve the hydrogenation effect in CoPd alloy.