스퍼터링 중 외부자기장이 자성박막의 자기적 특성에 미치는 영향

안현태 ( Hyun Tae Ahn ),임상호 ( Sang Ho Lim ),지광구 ( Kwang Koo Jee ),한준현 ( Jun Hyun Han ) 대한금속재료학회(구 대한금속학회) 2011 대한금속·재료학회지 Vol.49 No.6

A magnetic device which enables the application of a strong and uniform magnetic field to thin film during sputtering was designed for controlling the magnetic anisotropy using a three dimensional finite element method, and the effects of the external magnetic field on the magnetic properties of sputtered thin films were investigated. Both the intensity and the uniformity of the magnetic flux density in the sputter zone (50 mm ×50 mm) was dependent on not only the shape and size of the magnet device but also the magnitude of stray fields from the magnet. For the magnet device in which the distance between two magnets or two pure iron bars was 80-90 mm, the magnetic flux density along the direction normal to the external magnetic field direction was minimum. The two row magnets increased the magnetic flux density and uniformity along the external magnetic field direction. An Fe thin film sputtered using the optimized magnet device showed a higher remanence ratio than that fabricated under no external magnetic field.

Amorphous Ferromagnetic CoSiB/Pd Multilayer with Perpendicular Magnetic Anisotropy

정솔,임혜인,윤정범 한국물리학회 2013 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.62 No.1

Perpendicular magnetic anisotropy has been studied for possible use in high-density spin transfer torque magnetic random access memories. The key issues of high-density spin transfer torque magnetic random access memories are decreasing the switching current and have the high thermal stability. In order to solve these problems, the approach of developing a new amorphous ferromagnetic material for use as a pinned layer for a multilayer with a low saturated magnetization value has been suggested. In a previous study, amorphous ferromagnetic material CoSiB was shown to have a low saturated magnetization (M_s = 470 emu/cm³) and a modest anisotropy constant (K_u = 1,500 erg/cm³). Then, we investigated the perpendicular magnetic anisotropy of a [CoSiB t_CoSiB nm/Pt 1.4 nm]₅ multilayer, where t_CoSiB are 0.1, 0.2, 0.3, 0.4, and 0.5 nm. In this study, we present a new multilayer type based on the previous study, and this multilayer, CoSiB/Pd multilayer has the perpendicular magnetic anisotropy. In this letter, we have investigated the perpendicular magnetic anisotropies of a [CoSiB t_CoSiB nm/Pd 1.3 nm]₅ multilayer, where t_CoSiB are 0.1, 0.2, 0.3, 0.4, 0.5, and 0.6 nm and [CoSiB 6.3 nm/Pd t_Pd nm]₅ multilayer, where t_Pd are 1.1, 1.2, 1.3, 1.4, 1.5, and 1.6 nm.

Temperature dependent magnetic properties of Dy-doped Fe₁₆N₂: Potential rare-earth-lean permanent magnet

Khan, Imran,Park, Sungkyun,Hong, Jisang Elsevier 2019 INTERMETALLICS Vol.108 No.-

<P><B>Abstract</B></P> <P>Using the full potential linearized augmented plane wave method, we explored the magnetocrystalline anisotropy of Dy impurity doped α″-Fe<SUB>16</SUB>N<SUB>2</SUB>. Here, we considered two different Dy concentrations (1.56 and 3.125%). We also investigated the temperature dependence of the magnetic properties. The Dy site occupancy was found to be concentration dependent. The magnetic moments of Fe atoms near the Dy impurity was suppressed. However, we found a large magnetic moment in Dy atom (4.85–4.87 μ<SUB>B</SUB>). Compared with the magnetic anisotropy constant in the pristine α″-Fe<SUB>16</SUB>N<SUB>2</SUB> (0.57 MJ/m<SUP>3</SUP>), we obtained an enhanced perpendicular magnetic anisotropy. The calculated anisotropy constants in 1.56% Dy doping was 0.97 MJ/m<SUP>3</SUP> while it became 1.27 MJ/m<SUP>3</SUP> in 3.125% Dy doping. The Curie temperature in the pristine structure was about 820 K and it was suppressed to 765 K and 605 K in 1.56% and 3.125% Dy doping. At room temperature (300 K), the coercive field of 3.125% Dy doped system was enhanced almost 50% compared with that of the pure Fe<SUB>16</SUB>N<SUB>2</SUB>. We also found a maximum energy product of 50.9 MGOe for 3.125% Dy doping at 300 K. Our finding may suggest that the α″-Fe<SUB>16</SUB>N<SUB>2</SUB> can be a potential permanent magnet with a lean Dy doping.</P> <P><B>Highlights</B></P> <P> <UL> <LI> The spin-orbit coupling effect associated with Dy element mainly contributed to enhance the magnetocrystalline anisotropy. </LI> <LI> Perpendicular magnetocrystalline anisotropy was obtained for pure as well as Dy-doped α″-Fe<SUB>16</SUB>N<SUB>2</SUB>. </LI> <LI> The uniaxial anisotropy constant of 1.27 MJ/m<SUP>3</SUP> was obtained for 3.125 % Dy doping, and this is more than twice of Fe<SUB>16</SUB>N<SUB>2</SUB>. </LI> <LI> The H<SUB>C</SUB> and (BH)<SUB>max</SUB> was enhanced upto 50 % for 3.125 % Dy-doped system compared to the Fe<SUB>16</SUB>N<SUB>2</SUB> at room temperature. </LI> </UL> </P>

Strain mediated asymmetric response of the cation distribution on epitaxial CoFe₂O₄ films

Lee, Dooyong,Kim, Jiwoong,Cho, Chang-Woo,Bae, Jong-Seong,Won, Jonghan,Lee, Jouhahn,Park, Sungkyun Elsevier 2018 APPLIED SURFACE SCIENCE - Vol.447 No.-

<P><B>Abstract</B></P> <P>The asymmetric response of the cation distribution on [001] oriented CoFe<SUB>2</SUB>O<SUB>4</SUB> films were examined. Depending on the deposition temperature and substrates (MgO(0 0 1) or SrTiO<SUB>3</SUB>(0 0 1)), the films exhibited a range of compressive or tensile strain states along the out-of-plane. With increases in deposition temperature, the initial compressive (tensile) strain for the films grown on MgO(0 0 1) (SrTiO<SUB>3</SUB>(0 0 1)) was reduced. Furthermore, the out-of-plane (in-plane) magnetic anisotropy of the film grown on MgO(0 0 1) (SrTiO<SUB>3</SUB>(0 0 1)) decreased with increasing deposition temperature. The uniaxial magnetic anisotropy energy calculation based on the magnetic anisotropy (crystalline and shape) and strain of films confirmed that the strain reduction with increasing deposition temperature is the main source of the uniaxial magnetic anisotropy reduction, regardless of the sign of the strain. X-ray photoelectron spectroscopy explained the saturation magnetization variation by the cation distribution depending on the strain state. Furthermore, the calculated magnetic moment based on the cation distribution were well matched for the high crystalline films.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Epitaxial strain is reduced as the growth temperature is increased. </LI> <LI> Out-of-plane tensile trained films exhibit in-plane magnetic anisotropy. </LI> <LI> Uniaxial magnetic anisotropy energy decreases with decreasing out-of-plane strain. </LI> <LI> Depending on the strain state the opposite behavior of the cation distribution occurred. </LI> <LI> Variation of the saturation magnetization is related to the cation distribution. </LI> </UL> </P>

Out-of-plane Magnetic Anisotropy in Cleaved and Uncleaved CoS2

OMRAN Mariam,최준영,조연정,김미경,김창영 한국물리학회 2022 새물리 Vol.72 No.2

Magnetic anisotropy is an important phenomenon driven by a strong electron correlation. It is defined as the magnetization tendency of magnetic material in a particular crystallographic direction. In this paper, we investigated the magnetic anisotropy of CoS2 single crystal. Here, torque magnetometry was used to determine the magnetocrystalline anisotropy of the crystal. The angle dependence of torque () for CoS2 was measured at several temperatures above and below the ferromagnetic order transition Tc. To verify the effect of surface morphology on magnetic properties, we compared the () of uncleaved and cleaved pure CoS2. Results show that two-fold symmetry was equally dominant in both. Furthermore, we compared higher orders of magnetic anisotropy to track the intrinsic and shape anisotropies. All amplitudes showed the same behavior for cleaved and uncleaved samples, but the higher orders were more dominatant in the cleaved sample.

Magnetic domain structure and magnetic anisotropy in ferromagnetic Y₃Fe₅O₁₂ nanowires formed by step-edge decoration

Wook Shin, Hyun,Yeog Son, Jong North-Holland Pub. Co 2017 Journal of magnetism and magnetic materials Vol.444 No.-

<P><B>Abstract</B></P> <P>We investigated the ferromagnetic properties of Y<SUB>3</SUB>Fe<SUB>5</SUB>O<SUB>12</SUB> (yttrium iron garnet; YIG) nanowires deposited on a highly ordered pyrolytic graphite (HOPG) substrate. YIG nanowires with a diameter around 70nm were formed on the edges of terraces of the HOPG substrate using the step-edge decoration technique and pulsed laser deposition of the YIG. The magnetic field of the YIG nanowires was investigated; a ferromagnetic hysteresis loop was observed in the direction parallel to the nanowires, whereas anti-ferromagnetic hysteresis loops were observed perpendicular to the nanowire growth direction. Vertical and lateral magnetic force microscopy images of the ferromagnetic YIG nanowires revealed that the magnetization directions of the nanowires were parallel to the nanowires, which showed a single ferromagnetic domain.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Magnetic domain structure. </LI> <LI> Ferromagnetic properties of Y<SUB>3</SUB>Fe<SUB>5</SUB>O<SUB>12</SUB> (yttrium iron garnet; YIG) nanowires. </LI> <LI> Magnetic anisotropy. </LI> </UL> </P>

Site dependent enhancement of magnetic anisotropy in 4d and 5d impurity doped α″-Fe16N2: A first principles study

Imran Khan,홍지상 한국물리학회 2018 Current Applied Physics Vol.18 No.5

Using the first principles method, we studied the electronic structure and magnetocrystalline anisotropy of site dependent 4d, 5d element doping in α″-Fe16N2. We found that different Fe sites contributed differently for magnetocrystalline anisotropy. For instance, on d-site doping, we obtained perpendicular magnetocrystalline anisotropy while the h-site doping resulted in an in-plane magnetocrystalline anisotropy in all the studied systems. The impurity doping induces local lattice distortions near the impurity site. However, the volume of the cell and total magnetic moment of the doped systems were not much affected. This local lattice distortion together with the spin-orbit coupling effect associated with heavy 4d, 5d element mainly contributed to enhancing the magnetocrystalline anisotropy. The enhancement of the magnetocrystalline anisotropy results in almost 15 to 67% enhancement of the coercivity for 4d element doping while we found 80 to 137% enhancement for 5d element doping. The maximum energy products were also enhanced compared to the pure α″-Fe16N2. The maximum enhancement was observed in Rh and Pt doped systems where the energy products were 119–120 MGOe. These results may suggest that substitutional doped α″-Fe16N2 system can be used as potential rare earth free permanent magnet.

Enhancement of the Magnetic Anisotropy in Rare-Earth-Free Multilayer Fe16N2/Ag/Fe16N2 and Fe16N2/Au/Fe16N2

Imran Khan,홍지상 한국물리학회 2018 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.72 No.11

Using the first principles method, we investigated the interface effect on the electronic structure and the magnetic properties of multilayer Fe16N2/Ag/Fe16N2 and Fe16N2/Au/Fe16N2. The thicknesses of Ag (100) and Au (100) were fixed to three monolayers, and the lattice mismatch was about 1%. The magnetic moment of Fe atoms at the interface was suppressed due to hybridization with non-magnetic Ag and Au atoms. Due to this reduction in the magnetic moments and also because of the non-magnetic volume of the Ag and Au layer, an overall 40% suppression of the magnetization was found in both systems. The hybridization between interface Ag (Au) and Fe atoms and the spin-orbit coupling associated with Ag (Au) atoms mainly contributed to the enhancement of the magnetocrystalline anisotropy. The magnetocrystalline anisotropy constant was enhanced from 0.57 MJ/m3 in pure Fe16N2 to 1.58 MJ/m3 and 0.89 MJ/m3 in Fe16N2/Ag/Fe16N2 and Fe16N2/Au/Fe16N2 multilayer systems, respectively. This enhancement in magnetocrystalline anisotropy results in an enhancement of the coercive field. The coercive fields were about 30 and 16.7 kOe in the Ag and the Au multilayer systems, respectively. Overall, we found substantial enhancements in the magnetocrystalline anisotropy constant and the coercive field due to the interface effect. This finding may suggest that the Fe16N2/Ag/Fe16N2 and the Fe16N2/Au/Fe16N2 structures can be utilized for potential rare-earth-free permanent magnets.

Interfacial Perpendicular Magnetic Anisotropy in Magnetic Tunnel Junctions Comprising CoFeB with FeNiSiB Layers

Do Kyun Kim,Minhyeok Lee,Junghoon Joo,Young Keun Kim 대한금속·재료학회 2020 ELECTRONIC MATERIALS LETTERS Vol.16 No.1

Controlling ferromagnetic thickness (t) and properties such as saturation magnetization (Ms) and efective magnetic anisotropy constant (Kef) has been regarded as critical for the performance of magnetic tunnel junctions (MTJs) with interfacial perpendicular magnetic anisotropy. Here, we report the efects of hybridizing a CoFeB layer with a FeNiSiB layer as part of a magnetic free layer structure. We deposited thin flm stacks by magnetron sputtering on Si wafers with thermal oxides and carried out post-deposition heat treatment at 300 °C for 1 h in a vacuum under a magnetic feld. We found that Ms and Kef could be tuned by adding a layer of amorphous FeNiSiB. While the Ms and Kef values were modifed, the tunneling magnetoresistance (TMR) ratios of the MTJs were maintained, even though the CoFeB thickness was decreased by half. Moreover, an asymmetric bias voltage dependence of TMR was suppressed in the MTJs with FeNiSiB/CoFeB hybrid free layers due to improvements in the interface quality between the CoFeB/MgO interfaces.

High Perpendicular Magnetic Anisotropy of Electrodeposited Co-Pt Films

Geun-Hee Jeong,Chang-Hyoung Lee,In-Soo Park,Joo-Hee Jang,Su-Jeong Suh 한국물리학회 2008 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.52 No.6

Co-Pt alloy thin films were galvanostatically electrodeposited from an aqueous electrolyte consisting of Co sulphamate and PtP salt. A 30-nm-thick Ru buffer layer was used to enhance the perpendicular magnetic anisotropy. The Co-Pt thin films on a Ru buffer layer exhibited high perpendicular magnetic anisotropy. They also exhibited a as high out-of-plane coercivity and a high squareness of up to 6414 Oe and 0.86, respectively, without any heat treatment. The intrinsic perpendicular magnetic anisotropy constant, Kμ, of the Co-Pt alloy obtained using a torque magnetometer was 8.3 x 106 erg/cm³. The composition of the electrodeposited Co-Pt alloy was Co-25.19 at.% Pt corresponding to the Co₃Pt phase. According to the transmission electron microscopy (TEM) analysis, the out-of-plane coercivity and squareness increased significantly due to the growth of physically isolated columnar grains with the c-axis perpendicular to the film plane. Co-Pt alloy thin films were galvanostatically electrodeposited from an aqueous electrolyte consisting of Co sulphamate and PtP salt. A 30-nm-thick Ru buffer layer was used to enhance the perpendicular magnetic anisotropy. The Co-Pt thin films on a Ru buffer layer exhibited high perpendicular magnetic anisotropy. They also exhibited a as high out-of-plane coercivity and a high squareness of up to 6414 Oe and 0.86, respectively, without any heat treatment. The intrinsic perpendicular magnetic anisotropy constant, Kμ, of the Co-Pt alloy obtained using a torque magnetometer was 8.3 x 106 erg/cm³. The composition of the electrodeposited Co-Pt alloy was Co-25.19 at.% Pt corresponding to the Co₃Pt phase. According to the transmission electron microscopy (TEM) analysis, the out-of-plane coercivity and squareness increased significantly due to the growth of physically isolated columnar grains with the c-axis perpendicular to the film plane.