Suppression of Ferromagnetic Ordering in thicker co-sputtered Mn doped MgO Films
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Suppression of Ferromagnetic Ordering in thicker co-sputtered Mn doped MgO Films Sreekanth K. Mahadeva1,2, Zhi-Yong Quan1,3, J. C. Fan1,4, K. S. Sreelatha2,5, L. Belova1, Roman Puzniak5, K. V. Rao1 1. Department of Materials Science, Royal Institute of Technology, Stockholm, SE100 44 Sweden 2. Department of Physics, Amrita Vishwa Vidyapeetham University, Amritapuri Campus, Kollam, 690 525, Kerala, India 3. Key Laboratory of Magnetic Molecules and Magnetic Information Materials of Ministry of Education, Shanxi Normal University, Linfen, 041004, China 4. School of Materials and Engineering, Anhui University of Technology, Maanshan, 243002, China 5. Govt. Polytechnic College, Nattakom P O, Kottayam, 686 013, Kerala, India 6. Institute of Physics, Polish Academy of Sciences, Warszawa, Aleja Lotnikow , 32/46, PL-02668 Poland. ABSTRACT We report on preliminary studies of low (14 at.%) and high (53at.%) concentration Mn doped MgO films deposited by co-sputtering from metallic Mn and Mg targets. The structural, surface morphologies and magnetic properties of the films of different thickness were studied. All the as grown films are found to be amorphous and film surfaces are found to be flawless and homogeneous. We observe at room temperature robust ferromagnetic loops with a saturation magnetization value that is a function of film thickness reaching a maximum of ~38.5 emu/cm3 in the Mn0.53Mg0.47O film at a thickness of ~92 nm. In thicker films room-temperature ferromagnetic ordering is suppressed and eventually at a thickness around 120nm the expected diamagnetism of the bulk appears. The origin of ferromagnetism may be attributed to cation defects at the Mg-site. INTRODUCTION Research on the diluted magnetic oxides (DMOs) systems was initiated by the work of Matsumoto et al. [1] in the year 2000 with the observation of ferromagnetism in dilute cobalt doped TiO2 for potential application of spintronics, while the first wide band gap DMOs was reported earlier in Mn doped ZnO [2]. Since then intense research efforts have followed on these as well as other oxide systems with different transition metal and defect doping to realize robust room temperature ferromagnetism (RTFM). In recent few years, there have been many reports on RTFM associated both with and without transition elements doping in the rock-salt structured MgO, in which the ferromagnetism arises from defects [3-5]. An active defect is believed to interact with another closely situated active defect, and this eventually may lead to long range ferromagnetic ordering if the defects couple ferromagnetically. Recently we have reported ferromagnetic ordering in MgO thin films fabricated by sputtering [6]. It was found that magnetic moment averaged over film volume (saturation magnetization) increases almost linearly with increasing film thickness, and starts to decrease after reaching a maximum at a finite thickness. We have tested the above expectations in Mn doped MgO thin films deposited
on Si substrates by co-sputtering from metallic Mn and Mg targets in (Ar+O2)
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