雖然硬碟密度逐年的增加，但終究不是無窮的。或早或晚，我們勢必會撞上磁記錄的物理限制 -- 當記綠資料的顆粒過小時，光是溫度的改變，就足以將整個顆粒的磁極翻轉，導致資料的喪失或判定失敗。要能穩定的保存資料，大約要三百萬個磁性的原子一起才能辦得到。這次來自德國、法國和日本的聯合團隊找出來的方法，卻只要 51 個原子組成的分子，就能穩定地紀錄資料，這當中只有一顆是磁性的鐵原子，剩下來的是一層有機的保護層，保護中間的鐵原子不受影響。如果用這種技術做成的硬碟可以有現在五萬倍以上的容量，也就是說現在的 1TB 硬碟套用這種新技術，相同的體積可以儲存 50PB 的資料。更厲害的是，包在保護層中的分子同時還能改變它的磁力和導電力特性，也就是說除了可以用傳統的磁力方法（不同的磁極）來讀寫資料外，也可以用電力（改變電阻大小）來讀寫資料。換用之，同樣的技術可以做成傳統的硬碟磁盤，也可以做成純電力操作的阻憶體，果真是前途無量啊！
One bit of digital information stored on a hard disk currently consists of about 3 million magnetic atoms. Researchers from Karlsruhe, Strasbourg, and Japan have now developed a magnetic memory with one bit per molecule. By an electric pulse, the metal-organic molecule can be switched reliably between a conductive, magnetic state and a low-conductive, non-magnetic state. This novel correlation for molecules is now reported in the Nature Communications journal.
(doi: 10.1038/ncomms1940)
“The superparamagnetic effect prevents smaller bit sizes from being reached in a hard disk,“ explains Toshio Miyamachi, first author of the study and researcher at the Center for Functional Nanostructures (CFN) of Karlsruhe Institute of Technology (KIT). This superparamagnetic effect implies that magnetic memory crystals are increasingly susceptible to thermal switching with decreasing size. Consequently, information may soon be lost. “We chose another approach and placed a single magnetic iron atom in the center of an organic molecule consisting of 51 atoms. The organic shell protects the information stored in the central atom.” Apart from the ultimate density of one bit per molecule, this type of memory based on so-called spin crossover molecules also has the advantage of the writing process being reliable and purely electric.
“Using a scanning tunneling microscope, we applied defined electricity pulses to the nanometer-sized molecule,” adds Wulf Wulfhe-kel, head of the research group at KIT’s Physikalisches Institut. “This reproducibly changes not only the magnetic state of the iron, but also the electric properties of the molecule.” Hence, the two magnetic configurations lead to varying conductances, such that the magnetic state of the molecule can be determined easily by a simple resistance measurement.
The present study reports the fundamentals and shows the principle feasibility and advantages of memories consisting of spin crossover molecules. “These memristive and spintronic properties combined in a molecule will open up a new field of research,” the researchers are convinced. Memristors are memories that store information in the form of resistance variations. Spintronics uses the magnetic spin of individual particles for information processing.
Work was carried out at the laboratories of the Center for Functional Nanostructures (CFN) of KIT, the Institut de Physique et Chimie des Matériaux (IPCMS) in Strasbourg, the SOLEIL synchrotron in Paris, and the Chiba University, Japan.
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