Magnetic properties of ZnO-based diluted magnetic semiconductors

Abstract

We report a study of the magnetic properties of transition-metal doped Zn1−xTMxO (TM=Mn, Co, Fe). Polycrystalline powder samples were synthesized by both solid-state and liquid-phase reactions. From the Curie–Weiss behavior of susceptibility at high temperatures, it was found that the TM–TM interaction is dominated by antiferromagnetic coupling with effective nearest-neighbor exchange constants J=−90 to −30 K. The magnetization data measured at low temperature as a function field H are fit to a parameterized Brillouin function to obtain the effective concentration xeff of magnetically active TM2+ ions. As x increases, the fraction of magnetically active ions, xeff/x, decreases. This is ascribed to an increase in average AF interaction between doped magnetic spins as the average distance between them decreases with an increase in x.

Magnetic Fe doped ZnO nanofibers obtained by electrospinning

“…Additionally, based on a study of laser-deposited thin films of Zn 1-x Co x O, the antiferromagnetic super exchange interaction was proposed to be the dominant mechanism for the exchange coupling between Co and Zn 1-x Co x O [15]. Similar explanation was provided for polycrystalline powders synthesized by two different methods: solid-state and liquid-phase reactions [16]. The above observations have their foundation in calculations of the local spin density functional theory for Zn 1-x Co x [6].…”

Lattice location and thermal stability of implanted Fe in ZnO

“…Several reports on ferromagnetic systems based on ZnO can be found in the literature [1,[6][7][8][9][10][11][12][13][14]. Cases in which no ferromagnetic behavior was observed [7,[15][16][17][18] revealed systematic trends for the various transition metals, doping concentrations, and differences between n-and p-type ZnO, but also conflicting results between different authors. It was thus argued [11,14] that experimental reproducibility needs to be improved.…”

“…For instance, implants for producing ZnO diluted magnetic semiconductors were done with 250 keV 55 Mn or 59 Co up to fluences of 3-5×10 16 cm −2 , leading to concentration maxima around 3-5% [Norton 03, Theodoropoulou 03]. In future studies we will therefore also explore the 59 Fe lattice location in samples coimplanted with high doses of stable 56 Fe.…”

“…The exact nature of the ferromagnetism also remains unclear [1,8,11,13]; among possible problems are the formation of metallic TM or TM-oxide clusters [9,[12][13][14]17] or magnetism from the substrate on which thin films are deposited [18]. Two recent review papers on the subject concluded that a more precise control of the TM dopant in the oxide and careful structural and microstructural analyses are needed [1,11].Experimentally TM dopants have been introduced both during ZnO powder synthesis [10,14,16] and growth of epitaxial thin films [6][7][8][9]11,15,18]. In addition, ion implantation is also actively being explored for TM doping of ZnO [1,12,13,19].…”

“…Experimentally TM dopants have been introduced both during ZnO powder synthesis [10,14,16] and growth of epitaxial thin films [6][7][8][9]11,15,18]. In addition, ion implantation is also actively being explored for TM doping of ZnO [1,12,13,19].…”