Copyright © 2015 American Scientific Publishers All rights reserved Printed in the United States of America Article Journal of Nanoscience and Nanotechnology Vol. 15, 2356–2359, 2015 www.aspbs.com/jnn Magnetocrystalline Anisotropy of d 0 -Magnetic Material NaN(001) Thin Films: A Density Functional Study Soyoung Jekal 1 , Oryong Kwon 1 , Soon Cheol Hong 1 ∗ , and Jae Il Lee 2 1 Department of Physics and EHSRC, University of Ulsan, Ulsan 680-749, Republic of Korea 2 Department of Physics, Inha University, Incheon 402-751, Republic of Korea A bulk d 0 NaN of rocksalt or zinc-blende structure was predicted to be a ferromagnetic half metal and furthermore the half-metallicity would be retained in thin films. Such half metallicity of d 0 ferro- magnetic NaN is attractive for possible application in a spintronics device, such as a spin transfer torque magnetic random access memory. In this study, we carried out first-principles calculations on magnetocrystalline anisotropy rocksalt structured NaN thin films with different thicknesses, using Vienna Ab-initio Simulation Package code. It was found that the NaN(001) thin films have perpen- dicular magnetization with quite low magnetocrystalline anisotropy energies of order of 10 eV, but capping of a 5d-transition metal Ta monolayer over the NaN(001) thin films enhances the perpen- dicular magnetocrystalline anisotropy energies significantly, more than 10 times. Furthermore, the 1(Ta)/NaN(001) systems retain their half-metallicity except the NaN layer just below Ta. Keywords: Magnetic Materials, Thin Films, Surface Properties, Electronic Structure, Magnetic Structure. 1. INTRODUCTION The spin transfer torque (STT) phenomenon is an emerg- ing solution to commercialize non-volatile magneto resis- tive random access memory (MRAM). A conventional MRAM, which uses a magnetic field to switch the mag- netic direction, 1 has a problem in selectivity of a magnetic bit in writing due to a stray magnetic field. In a STT- MRAM, a localized spin current 2 within a bit leads to excellent writing selectivity. 3 Additionally, a STT-MRAM has other advantages over a conventional MRAM, such as high scalability, low power consumption, simpler architec- ture, and faster operation. However, a STT MRAM has still two “must-overcome” obstacles: (i) high critical current density 4 for switching magnetic direction of a bit and (ii) thermal instability, 5 caused by superparamagnetism in connection with getting smaller magnetic bit. The critical current to reverse magnetic direction is given by I C = 2e ℏ  g M S V H K + 2M S  (1) ∗ Author to whom correspondence should be addressed. where  is the Gilbert’s damping constant, g is a factor of spin polarization, M s is saturation magnetization, V is volume, and H k is an anisotropy field. To reduce the criti- cal current, it is neccessary to increase g and decrease M s , V , and H k . On the other hand, the formula for thermal stability, a key factor for a spintronics devise, is given by  = KV k B T (2) where K is an anisotropy constant, T is the temperature, and k B is the Boltzmann constant. Increasing K and V is necessary for thermal stability. To satisfy low critical current and high thermal stability simultaneously, a mate- rial with high perpendicular magnetocrystalline anisotropy (MCA) energy and high spin polarization must be used in a STT-MRAM. Because a half-metallic material has 100% spin polarization at the Fermi level, it is advantageous in the reducing the critical current. Rocksalt and zinc-blende structured NaN alloys were predicted to be half-metallic, 6 not only in bulk but also in a thin film. 7 When the bit size of MRAM gets smaller, a half-metal material with high perpendicular MCA energy 8 may reduce the critical current, while concurrently retain- ing thermal stability [see Eqs. (1) and (2)]. In this study, 2356 J. Nanosci. Nanotechnol. 2015, Vol. 15, No. 3 1533-4880/2015/15/2356/004 doi:10.1166/jnn.2015.10264