FIRST-PRINCIPLE INVESTIGATION ON ELECTRONIC AND MAGNETIC PROPERTIES OF OXIDE-DILUTED MAGNETIC SEMICONDUCTOR

1.Abstract

Spintronics devices have attracted investigations due to their high performance compared with conventional electronic devices. One of potential materials is diluted magnetic semiconductor (DMS). Early DMS has low-temperature ferromagnetism. Room-temperature ferromagnetism is required for real device applications. Oxide-based DMS is one of great idea for obtaining room-temperature ferromagnetism, motivated by ferromagnetism found in Co-doped anatase TiO2 in 2001.
In our research, we investigate electronic and magnetic properties of TiO2-based systems in rutile, anatase, and brookite phases within density functional theory (DFT) method. Our goals of research is to study crystal models and pseudopotentials (PP), to optimize the system model and comparing the system with previous results, either theoretical or experimental results, and to deeply investigate the electronic and magnetic properties of TiO2 doped by pentavalent transition metals (TM) (V, Nb, or Ta) or ferromagnetic (Co, Fe, Ni) TMs. Further investigations will be performed with codoping case involving one pentavalent and one ferromagnetic TMs, compared with relevant results in relevent publications by experimental or/and theoretical investigations.
In a way reminiscent of DMS case, we must put the dopants in our host system (TiO2) with small concentration. Hence, large supercells up to 4 � 4 � 4 supercell are required to put one atom or few atoms in the host system with variated concentration from about 0.2% up to 12% for the three titania polymorphs, which is comparable with previous concentration in Co-doped rutile TiO2 system.
In order to effectively calculate the systems, we propose to use high performance computing (HPC) using Quantum-ESSPRESSO 5.1 software, which is available in GRID LIPI. The more detailed requirements are presented in research methodology chapter in this proposal.
 

2.Keywords
diluted magnetic semiconductor, TiO2, density functional theory, room-temperature ferromagnetism, Quantum-ESSPRESSO 5.1
3.Objective

Our first goal of research is to study crystal models and pseudopotentials (PP) used in calculation. Second goal is to optimize the system model and comparing the system with previous results, either theoretical or experimental results. Third goal is to deeply investigate the electronic and magnetic properties of TiO2 doped by pentavalent transition metals (TM) (V, Nb, or Ta) or ferromagnetic (Co, Fe, Ni) TMs

4.Methodology

In a way reminiscent of DMS case, we must put the dopants in our host system (TiO2) with small concentration. Hence, large supercells up to 4 � 4 � 4 supercell are required to put one atom or few atoms in the host system with variated concentration from about 0.2% up to 12% for the three titania polymorphs, which is comparable with previous concentration in Co-doped rutile TiO2 system. In order to effectively calculate the systems, we propose to use Quantum-ESSPRESSO (QE) (Gianozzi et al, 2009) which is available in Grid LIPI for 5.1 version (http://grid.lipi.go.id/main/navigate/info_software), while to visualize the crystal models in three-dimensional (3D) pictures, we use XCrysDEN atau (X-Window) Crystalline Structures and Densities (Kokalj, 1999; Kokalj, 2003) which is available in our computer after obtaining results from Grid LIPI HPC Cluster.

In this research, dopant atoms used are pentavalent transition metals (V, Nb, Ta) and ferromagnetic transition metals (Co, Fe, Ni). In this proposal, we put examples of our models

The calculation will be performed in three main steps and two post-processing steps. The first step is self-consistent field (SCF) calculation added with relaxation calculation to obtain ground state and most stable condition (command : pw.x). The second step is band structure calculation followed by its post-processing (command : bands.x). The band structure calculation will be performed using high symmetry k-point. The third step is non-SCF calculation followed by its post-processing (command : projwfc.x) to extract the total density of states (DOS) and projected-DOS as function of energy levels.

 

5.Team

Shibghatullah Muhammady

6.Computation plan (required processor core hours, data storage, software, etc)

We allocate the schedule from April 2016 to May 2017 (as shown in Tabel II in proposal file). The allocated time of HPC cluster using is until 2017. This time is related to the plan of doctoral dissertation examination. If available, extended time is proposed later for more publications, of course, with acknowledgement to Grid LIPI.

To succesfully perform the planned calculation, we need minimum 48-hours calculation which requires total data storage of about 80 GB to 200 GB for each model based on our experience, especillay for high supercell (such as 4 � 4 � 4 or even more if necessary) and high k-potnt mesh models. The calculation will be performed in parallel for two until five models to, as example, performed variable-dependence calculation. Hence, the allocation requires is up to 400 GB. In spite of planned 48-hours calculation, we use restart_mode = �restart� in the QE routine. The required calculation node is high-valued node with high random access memory (RAM) value to obtain fast calculation and, further, fast data gain, effectively. We thus proposed for using the Basic Node in Cibinong (80 nodes) or Bandung (34 nodes) (http://grid.lipi.go.id/main/navigate/info_facilities) due to our big data using plan.

7.Source of funding
1st Batch Program Menuju Doktor Sarjana Unggul (PMDSU) scholarship
8.Target/outputs
Two international publications and two international conference proceeding
9.Date of usage
29/04/2016 - 31/05/2017
10.Gpu usage
-
11.Supporting files
prop_1461115561.pdf
12.Created at
20/04/2016
13.Approval status
approved