The ferromagnetic ordering in Mn-doped ZnO thin films grown by way of pulsed laser deposition (PLD) as a function of oxygen constraining force and substrate temperature has been investigated.

The ferromagnetic ordering in Mn-doped ZnO thin films grown by way of pulsed laser deposition (PLD) as a function of oxygen constraining force and substrate temperature has been investigated. Room-temperature ferromagnetic behaviors in the Mn-doped ZnO films grown at 700?°C and 800?°C subordinate to 10^sup -1^ torr in oxygen influence were found, whereas ferromagnetic ordering in the films grown subordinate to 10^sup -3^ torr disappeared at 300 K The large positive magnetoresistance (MR) ~10% was observ at 5 K at grave fields and small negative MR was observ at high fields, irrespective of oxygen hurry In particular, anomalous Hall efficiency (AHE) in the Mn-doped ZnO film grown at 700?°C in a less degree than 10^sup -1^ Torr has been observ up to 210 K In this work, the observ AHE is believed to be further direct evidence demonstrating that the Mn-doped ZnO thin films are ferromagnetic.

Key words: Diluted magnetic semiconductors (DMSs) Mn-doped ZnO, anomalous Hall tenor (AHE), pulsed laser deposition (PLD) oxygen influence ferromagnetism

INTRODUCTION

Diluted magnetic semiconductors (DMSs) have attracted greatly interest in recent years fit to their possibility of exploiting charge and spin grades of freedom to bring novel functionalities to semiconductor devices.1-21 In particular, wide bandgap semiconductors continue to be of central importance, since Dietl et al.2 predicted T^sub c^ exceeding apartment temperature for GaN and ZnO containing 5% of Mn and a high retreat concentration (3.5 ?— 10^sup 20^ cm^sup -3^) lately although Mn-doped GaN3-5 and Mn-doped ZnO6-17 have been intensively studied, the origins of their ferromagnetism are still not entirely understood.

II-VI DMSs of the like kind as ZnO are of particular significance because the solubility limit of magnetic ions is actual high. However, the magnetic behaviors of Mn-doped ZnO differ for different research form into groupss for instance, which reported Mn-doped ZnO to be antiferromagnetic7 and paramagnetic8,11 and ferromagnetic.9,10,12-17 plane the origins of ferromagnetic ordering were controversially reported proper to a change of electronic band structure9 a carrier-induced mechanism,12 or an oxygen-vacancy-stabilized metastable ferromagnetic phase.16 The discrepancies can be attributed to different sample growing conditions or different sample growing systems e.g., pulsed laser deposition (PLD)781215-17 laser molecular-beam epitaxy,9 ion implantation,10 magnetron sputtering,11 and standard solid-state reaction.6 Furthermore, the magnetic properties of Mn-doped ZnO can be sensitive to Mn contented and growth conditions, e.g., substrate temperature, oxygen crushing and so on.

In the current work, we report the magnetic and magnetotransport properties of Mn-doped ZnO thin films grown by way of PLD as a function of oxygen press and substrate temperature. The origin of room-temperature ferromagnetism in the Mn-doped ZnO films grown at high oxygen compressing is discussed.

EXPERIMENT

Mn-doped ZnO thin films in the thickness range 20-50 nm were grown on PLD on a single-crystal sapphire substrate using ZnMnO targets with 30% of Mn concentrations. The deposition time on ablating targets with Nd:YAG laser (355 nm) and laser vibration energy density were 8.5 min and 2J/cm^sup 2^ respectively. The films were grown at various substrate temperatures ranging from 20?°C to 800?°C in a less degree than oxygen pressure of 10^sup -1^ to 10^sup -3^ torr. X-ray diffraction (XRD) technique and high-resolution transmission electron microscopy (HRTEM) were used to investigate the crystal pile and microstructure of the Mn-doped ZnO thin films. TEM-electron dispersive spectrometry was also used to estimate Mn peace in the films. The van der Pauw Hall and magnetoresistance (MR) measurements were performed by the agency of applying a magnetic field up to 9 T in the temperature range 4-300 K in order to investigate the electrical and magnetotransport properties of the Mn-doped ZnO films. Hysteresis apertures were measured at temperatures ranging from 4 K to 300 K using a superconducting quantum interference device.

RESULT AND DISCUSSION

The crystal composition of the 26at.%Mn-doped ZnO film grown at 700?°C beneath 10^sup -1^ torr in oxygen urgency was investigated by XRD. Figure 1 point outs the XRD pattern for the film in which all the peaks were build to be from the wurtzite construction of ZnO, except for peaks of (013) (223) from Zn^sub 2^Mn^sub 3^O^sub 8^ As reported in a previous study18 Zn^sub 2^Mn^sub 3^O^sub 8^ is believed not to be responsible for the origin of ferromagnetic ordering in the Mn-doped ZnO films, since it is nonmagnetic. A representative HRTEM image (see the inset of Fig. 1) provides direct experimental evidence that there are no appreciable Mn nanoclusters or Mn oxides as a secondary phase in the Mn-doped ZnO film, which is suspected to exhibit ferromagnetic ordering in the film. Our be the effects on the crystal structure and microstructures are crucial in addressing the intrinsic origin of ferromagnetic ordering in the Mn-doped ZnO plans

Fig. 1. XRD pattern of the film grown at 700?°C in a less degree than 10^sup -1^ torron the Al^sub 2^O^sub 3^ substrate. The inset is a cross-sectional HRTEM image of 26% Mn-ZnO showing no indication of any embedded Mn clusters or Mn oxides.