Characterization of Room-Temperature Ferromagnetic Zn1-xCoxO Nanowires

Abstract

The manipulation and detection of an electron's charge and, simultaneously, its spin orientation in electronic devices have been developed to be a new emerging field of spintronics (or magnetoelectronics) (Prinz, 98; Wolf et al., 2001). At present, the most notable spintronic applications could be the hard disk read heads and the magnetic random access memory which are based on metal magnetic materials and are assorted into metallic spintronic devices. The establishment of metallic spintronics might be ascribed to a discovery of giant magnetoresistance (Baibich et al., 1988; Binasch et al., 1989) and, subsequently, understanding and exercise of a spin-valve scheme (Moodera et al., 1995), and tunnelling magnetoresistance (Dieny et al., 1991) in ferromagnetic multilayers. On the other hand, in order to integrate with the modern industrial technology, new semiconductor materials such as diluted magnetic semiconductors (DMSs) (Furdyna, 1988), also known as ferromagnetic semiconductors (Ohno, 1998), have been searched for a supply of a spinpolarized carrier source. Those devices building on a transport of spin current in semiconductors are categorized into semiconductor spintronics. Spin injection, maintenance of a spin coherence, spin detection, and a spin carrier source in semiconductors are all important issues for semiconductor spintronics. The DMSs, based on host materials of II-VI and IV-VI semiconductors, have been studied for several decades. Although the indirect exchange mechanisms between 3d transition metal dopants in these semiconductors have been inspected experimentally and discussed theoretically (Story et al., 1986; Sawicki et al., 1986; Furdyna, 1988) for a long time, the Curie temperature (TC), below which a spontaneous magnetization and a spin-polarized current in the DMSs arise, was too low to be capable of employment. Until recent advance in III-V DMSs of (In,Mn)As and (Ga,Mn)As (Ohno et al., 1996), TC’s of some new DMSs such as (Ga,Mn)As have been raised up to ~110 K. These new III-V DMS materials were exploited to demonstrate tunneling magnetoresistance in (Ga,Mn)As ultrathin heterostructures (Hayashi et al., 1999), electrical spin injection in a ferromagnetic semiconductor heterostructure (Ohno et al., 1999), electric-field control of ferromagnetism (Ohno et al., 2000}, electrical manipulation of magnetization reversal (Chiba et al., 2003), and current-induced domainwall switching (Yamanouchi et al., 2004). On the other hand, the other approach of spincurrent injection into semiconductors from ferromagnetic metals has recently been achieved, so as to realize semiconductor spintronics at room temperature.