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Gigantic perpendicular magnetic anisotropy of heavy transition metal cappings on Fe/MgO(001)
Taivansaikhan, P.,Odkhuu, D.,Rhim, S.H.,Hong, S.C. North-Holland Pub. Co 2017 Journal of magnetism and magnetic materials Vol.442 No.-
<P><B>Abstract</B></P> <P>Effects of capping layer by 5<I>d</I> transition metals (TM=Hf, Ta, W, Re, Os, Ir, Pt, and Au) on Fe/MgO(001), a typical magnetic tunneling junction, are systematically investigated using first-principles calculation for magnetism and magnetocrystalline-anisotropy (MCA). The early TMs having less than half-filled <I>d</I> bands favor magnetization antiparallel to Fe, whereas the late TMs having more than half-filled <I>d</I> bands favor parallel, which is explained in the framework of kinetic exchange energy. The Os capping, isovalent to Fe, enhances MCA significantly to gigantic energy of +11.31meV/cell, where positive contribution is mostly from the partially filled majority <I>d</I> bands of magnetic quantum number of |m|=1 along with stronger spin-orbit coupling of Os than Fe. Different TM cappings give different MCA energies as the Fermi level shifts according to the valence of TM: Re and Ir, just one valence more or less than Os, have still large PMCA but smaller than the Os. In the W and Pt cappings, valence difference by two, PMCA are further reduced; MCAs are lowered compared to Fe/MgO(001) by the cappings of the very early TMs (Hf and Ta), while the very late TM (Au) switches sign to in-plane MCA.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Effects of capping layer by 5<I>d</I> transition metals on MCA of Fe/MgO(001) are systematically investigated. </LI> <LI> The Os capping, isovalent to Fe, enhances MCA significantly to gigantic MCA energy of +11.31meV/cell. </LI> <LI> The early TMs having less than half-filled <I>d</I> bands favor magnetization antiparallel to Fe. </LI> <LI> The late TMs having more than half-filled <I>d</I> bands favor magnetization parallel to Fe. </LI> <LI> The magnetization behaviors of TMs is explained in terms of kinetic exchange energy. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>MCA energies (E<SUB>MCA</SUB>) of 5<I>d</I> TM/Fe/MgO(001). For reference, the red-dashed line represents that of Fe/MgO(001). The Os capping, isovalent to Fe, enhances MCA significantly to gigantic energy of +11.31meV/cell.</P> <P>[DISPLAY OMISSION]</P>
Inducing and manipulating magnetization in 2D zinc–oxide by strain and external voltage
Taivansaikhan, P,Tsevelmaa, T,Rhim, S H,Hong, S C,Odkhuu, D IOP 2018 Journal of Physics, Condensed Matter Vol.30 No.14
<P>Two-dimensional (2D) structures that exhibit intriguing magnetic phenomena such as perpendicular magnetic anisotropy and its switchable feature are of great interests in spintronics research. Herein, the density functional theory studies reveal the critical impacts of strain and external gating on vacancy-induced magnetism and its spin direction in a graphene-like single layer of zinc oxide (ZnO). In contrast to the pristine and defective ZnO with an O-vacancy, the presence of a Zn-vacancy induces significant magnetic moments to its first neighboring O and Zn atoms due to the charge deficit. We further predict that the direction of magnetization easy axis reverses from an in-plane to perpendicular orientation under a practically achievable biaxial compressive strain of only ~1–2% or applying an electric field by means of the charge density modulation. This magnetization reversal is mainly driven by the strain- and electric-field-induced changes in the spin–orbit coupled <I>d</I> states of the first-neighbor Zn atom to a Zn-vacancy. These findings open interesting prospects for exploiting strain and electric field engineering to manipulate magnetism and magnetization orientation of 2D materials.</P>
Taivansaikhan, P,Odkhuu, D,Kwon, O R,Tsogbadrakh, N,Hong, S C American Scientific Publishers 2014 Journal of Nanoscience and Nanotechnology Vol.14 No.12
<P>We systematically investigate the effects of having Pt as a substrate and/or capping layer on the magnetism and magnetocrystalline anisotropy (MCA) of 3d transition metal (TMs; Cr, Mn, Fe, and Co) monolayers (MLs) by using a first-principles calculationl method. We found that Fe and Co MLs are ferromagnetic (FM) on a Pt(001) surface, but Mn and Cr MLs are antiferromagnetic (AFM). The magnetic moments are quite robust with additional Pt-capping. Furthermore, Pt-capping enhances the small perpendicular MCA (meV) of Fe/Pt(001) significantly to 4.44 meV. Our electronic structure analyses indicate that strong hybridization between Pt-5d and TM-3d orbitals plays a crucial role in determining magnetic ordering and MCA. For comparison we also calculated magnetism and MCA of 3d TM MLs on Ta(001) with and without Ta-capping.</P>