Correlation between Ferromagnetic Layer Easy Axis and the Tilt Angle of Self Assembled Chiral Molecules

The spin-spin interactions between chiral molecules and ferromagnetic metals were found to be strongly affected by the chiral induced spin selectivity effect. Previous works unraveled two complementary phenomena: magnetization reorientation of ferromagnetic thin film upon adsorption of chiral molecules and different interaction rate of opposite enantiomers with a magnetic substrate. These phenomena were all observed when the easy axis of the ferromagnet was out of plane. In this work, the effects of the ferromagnetic easy axis direction, on both the chiral molecular monolayer tilt angle and the magnetization reorientation of the magnetic substrate, are studied using magnetic force microscopy. We have also studied the effect of an applied external magnetic field during the adsorption process. Our results show a clear correlation between the ferromagnetic layer easy axis direction and the tilt angle of the bonded molecules. This tilt angle was found to be larger for an in plane easy axis as compared to an out of plane easy axis. Adsorption under external magnetic field shows that magnetization reorientation occurs also after the adsorption event. These findings show that the interaction between chiral molecules and ferromagnetic layers stabilizes the magnetic reorientation, even after the adsorption, and strongly depends on the anisotropy of the magnetic substrate. This unique behavior is important for developing enantiomer separation techniques using magnetic substrates

Magnetic Anisotropy in Co/Nd Multilayers with Depth-Selectively Inserted 57\text{}^{57}Fe Probe Layer

Multilayers of Co/Nd with probe layer of 2 Å of $\text{}^{57}$Fe evaporated in UHV conditions were studied by means of vibrating sample magnetometry and Mössbauer spectroscopy at T = 4.2 K. Isomer shift, hyperfine field distribution and direction was obtained from the Mössbauer data computer fitting. Magnetic anisotropy was studied and discussed. The easy magnetization direction was close to the perpendicular direction for both samples but the tendency to perpendicular anisotropy was stronger when the Fe probe layer was placed in the vicinity of Co/Nd interface

Drastic changes of the domain size in an ultrathin magnetic film

A general framework for the domain size in any ultrathin film with perpendicular magnetic anisotropy is here discussed. The domain structure is analyzed by using the classical theory taking into consideration the demagnetization field contribution to the domain wall energy. A sinusoidal model is considered to describe the domain structure while approaching, in two different cases, the monodomain state with in-plane magnetization. The first case is realized applying a large enough in-plane magnetic field. The second one is obtained by decreasing the perpendicular magnetic anisotropy, which is connected in many ultrathin systems with the increase of film thickness. A change in the domain size of several orders of magnitude is obtained while approaching the magnetization reorientation region. The minimal stripe domain period p=8πlex2/d is calculated from the sinusoidal model, where lex is the exchange length and d is the thickness of the film. The range of possible domain size changes in ultrathin films is predicted. The domain size has been experimentally studied in a 1 nm Co film characterized by a square hysteresis loop. The investigations have been performed by polar Kerr based microscopy and magnetic force microscopy. The domain structure of two remnant states generated by applying an in-plane and a perpendicular magnetic field has been compared. Drastically, the smallest domain size has been observed for the former.The authors are grateful to Professor J. Miltat for fruitful discussions concerning MFM imaging and Dr. M. Tekielak for magneto-optical imaging. J. M. Garcia wishes to thank the European Community for his Marie Curie Fellowship. This work was supported by the Polish State Committee for Scientific Research (Grant No. 4 T08A 025 23), ESF NANOMAG project and European Commission program ICA1-CT-2000-70018 (Center of Excellence CELDIS).Peer reviewe

Grazing Incidence X-Ray Reflectivity Study of MBE-Grown Co/Cu Multilayers

In this work we report preliminary grazing-incidence X-ray reflectometry studies of multilayer structures composed of 3d metals Co and Cu deposited in the ultra-high vacuum molecular beam epitaxy system. The multilayers of different modulation period were deposited on glass substrate directly, or on 3d -metallic buffers of various thicknesses. The experimental specular reflectivity spectra were analyzed by a comparison with a theoretical model calculated from a recursive algorithm based on the Fresnel formula [1, 2]. It enabled us to estimate the structural parameters concerning layer thickness and roughness. The results obtained are correlated with magnetization measurements of the layered structures, as a function of modulation period, buffer type and thickness. A special attention to influence of interfacial roughness on magnetization results is paid

Stm Observed Surface Structures and Magnetic Properties of MBE-Grown Metallic Thin Films

Rare-earth epitaxial thin films of Tb and Gd of the thicknesses betweeRare-earth epitaxial thin films of Tb and Gd of the thicknesses between 2 nm and 16 nm were deposited by means of molecular beam epitaxy method. The roughness of the rare-earth films measured by scanning tunneling microscopy was found to be in the range of 1-4.5 nm. The influence of the roughness on the dipolar anisotropy and magnetocrystalline surface anisotropy was estimated. The magnetic measurements have shown that the Gd layers deposited on the Y buffer layers had an easy plane anisotropy. However, for 2 nm thick Gd layer deposited on W buffer layer the perpendicular anisotropy was observed. According to the roughness analysis the possible sources of the perpendicular anisotropy in this sample is mainly the magnetoelastic anisotropy, but the presence of the magnetocrystalline surface anisotropy also cannot be neglected.n 2 nm and 16 nm were deposited by means of molecular beam epitaxy method. The roughness of the rare-earth films measured by scanning tunneling microscopy was found to be in the range of 1-4.5 nm. The influence of the roughness on the dipolar anisotropy and magnetocrystalline surface anisotropy was estimated. The magnetic measurements have shown that the Gd layers deposited on the Y buffer layers had an easy plane anisotropy. However, for 2 nm thick Gd layer deposited on W buffer layer the perpendicular anisotropy was observed. According to the roughness analysis the possible sources of the perpendicular anisotropy in this sample is mainly the magnetoelastic anisotropy, but the presence of the magnetocrystalline surface anisotropy also cannot be neglected

Preisach Maps of Multilayered Co/Cu Structures

Magnetooptical Kerr effect measurements of room temperature hysteresis loops were taken using sandwich- and multilayer-type specimens and He-Ne laser light. For maximal external field of ~250 Gs the corresponding Kerr angle reached 0.04 deg. The samples were obtained in the Institute of Physics, Polish Academy of Sciences, Warszawa, using MBE method. The structure of samples may be described by a formula: substrate-buffer layer-(xCo/yCu)$\text{}_{n}$ -cover layer. Al$\text{}_{2}$O$\text{}_{3}$ (two orientations) and MgO were used as substrates, the buffer layer was made of W, Cu or Fe, x=15, 20 or 25 Å, y=7, 8, 9, 10, 11, 12, 13, 14, and 20 Å, n=25 and 30. 50 Å of gold (Au) served as a cover layer. The genetic algorithm was subsequently used as a data processing tool, in order to reconstruct the Preisach map for each hysteresis loop. The diagrams clearly indicate changes of magnetic interactions caused by varying thicknesses of individual magnetic and non-magnetic layers

Formation of magnetic dots in an ultrathin Co film forced by a patterned buffer

The novel method for fabricating magnetic dots reported in this work exploits the dependence of the magnetic anisotropy of an ultrathin Co film on its thickness and on the type of the buffer layer. A patterned buffer prepared as self-assembled Au islands with a lateral size of several hundred nanometres grown on a Mo film surface induces mono-domain dots magnetized perpendicularly to the film plane in the epitaxial Co layer. Polar magneto-optical Kerr magnetometry and magnetic force microscopy have been used to investigate the magnetization reversal of the dots. Nucleation of the reversed magnetic domain followed by the unpinned movement of domain walls is discussed as a possible mechanism responsible for magnetization switching

Structural study of Co/Gd multilayers by X-ray diffraction and GIXR

The objective of this work was the structural characterisation of Co/Gd multilayers grown by MBE process in various conditions. such as substrate composition, growth temperature, presence of buffer laver, bilayer thickness and thickness ratio of constituent sublayers. The structure of the sublayers and interfaces was studied by X-ray diffraction and grazing-incidence X-ray reflectivity (GIXR). The samples have been characterised by a conventional X-ray source as well as by synchrotron radiation, The obtained results show the enhanced diffusion of Co into Gd leading to thickness reduction of the pure Co sublayers. Simulations of the measured reflectivity suggest that a complex electron density profile occurs in the Co/Gd multilayers and the interfacial roughness of the Co/Gd interface differs from the roughness of the Gd/Co interface. (C) 2001 Elsevier Science B.V. All rights reserved

ATOMIC STRUCTURE AND MAGNETIC PROPERTIES OF RARE-EARTH-IRON MULTILAYERS

Mössbauer spectroscopy and magnetization measurements were carried out on Fe-RE multilayers where RE=Nd, Tm. Perpendicular and in-plane anisotropy direction for Nd-Fe and Tm-Fe multilayers was respectively observed. The atomic structure was studied by Mössbauer spectroscopy, small angle X ray scattering and transmission electron microscopy. The structure of the layers is built from pure iron and pure neodynium sandwiching a NdFe paracrystalline interface layer. We demonstrate that multilayer structure can be used to give a choosen magnetic anisotropy