Probing the Magnetic Exchange Forces of Iron on the Atomic Scale

Schmidt, R.; Lazo, Cesar; Hölscher, Hendrik; Pi, Ung Hwan; Caciuc, Vasile; Schwarz, Alexander; Wiesendanger, R.; Heinze, Stefan

doi:10.1021/nl802770x

Cited by 49 publications

(44 citation statements)

References 22 publications

(41 reference statements)

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“…By simulating MExFM images, one can explain the contrasts observed in recent experiments and show that they are due to a competition between chemical and magnetic forces. 38 Concerning SP-STM, we estimate the effect of tip-sample relaxations on the experimental corrugation amplitude, i.e., the maximum vertical tip height change while scanning the surface in the constant-current mode. We find that at a tipsample separation of 4 Å the corrugation amplitude due to relaxations is of similar magnitude as the contribution from the spin-polarized tunneling current.…”

Section: Introductionmentioning

confidence: 99%

Role of tip size, orientation, and structural relaxations in first-principles studies of magnetic exchange force microscopy and spin-polarized scanning tunneling microscopy

Lazo

Caciuc

Hölscher³

et al. 2008

Phys. Rev. B

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Using first-principles calculations based on density-functional theory, we investigated the exchange interaction between a magnetic tip and a magnetic sample which is detected in magnetic exchange force microscopy ͑MExFM͒ and also occurs in spin-polarized scanning tunneling microscopy ͑SP-STM͒ experiments. As a model tip-sample system, we chose Fe tips and one monolayer Fe on W͑001͒ which exhibits a checkerboard antiferromagnetic structure and has been previously studied with both SP-STM and MExFM. We calculated the exchange forces and energies as a function of tip-sample distance using different tip models ranging from single Fe atoms to Fe pyramids consisting of up to fourteen atoms. We find that modeling the tip by a single Fe atom leads to qualitatively different tip-sample interactions than using clusters consisting of several atoms. Increasing the cluster size changes the calculated forces, quantitatively enhancing the detectable exchange forces. Rotating the tip with respect to the surface unit cell has only a small influence on the tip-sample forces. Interestingly, the exchange forces on the tip atoms in the nearest and next-nearest layers from the apex atom are non-negligible and can be opposite to that on the apex atom for a small tip. In addition, the apex atom interacts not only with the surface atoms underneath but also with nearest neighbors in the surface. We find that structural relaxations of tip and sample due to their interaction depend sensitively on the magnetic alignment of the two systems. As a result the onset of significant exchange forces is shifted toward larger tip-sample separations which facilitates their measurement in MExFM. At small tip-sample separations, structural relaxations of tip apex and surface atoms can either enhance or reduce the magnetic contrast measured in SP-STM.

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Section: Introductionmentioning

confidence: 99%

Role of tip size, orientation, and structural relaxations in first-principles studies of magnetic exchange force microscopy and spin-polarized scanning tunneling microscopy

Lazo

Caciuc

Hölscher³

et al. 2008

Phys. Rev. B

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“…Thereby, carbon segregates to the surface, where is reacts with oxygen into CO that desorbs. A final high temperature flash ( The c(2 × 2) pattern on the monolayer shows that the tip is magnetically sensitive [5]. c Atomically resolved 3D-MExFS data recorded on the Fe monolayer with such a tip.…”

Section: Sample Preparationmentioning

confidence: 99%

“…2 of this book). After it became possible to image magnetic structures with atomic resolution on insulators [4,18] as well as on metals [5], this technique was also employed to obtain more quantitative information about the short range magnetic tip-sample interaction [6,18]. Noteworthy, such quantitative data can become also relevant for spin-polarized scanning tunneling microscopy (SP-STM) and spectroscopy (SP-STS) experiments, if the tip gets very close to the sample, i.e., during conductance [7] or spin-friction experiments [8].…”

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Magnetic Exchange Force Spectroscopy

Schwarz

Heinze

2015

Noncontact Atomic Force Microscopy

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Magnetic exchange force spectroscopy is an elegant experimental method to extract the short-range magnetic contribution to the total interatomic interaction energy between the tip apex atom and the sample atoms across a vacuum gap. If the tip does not exhibit a spin-dependent reversible hysteretic reconfiguration of its atomic structure, experimental data can be directly compared quantitatively with first principles electronic structure calculations. Moreover, knowing the distance dependence and magnitude of the magnetic exchange interaction opens a new route to induce magnetization reversal events. IntroductionForce spectroscopy is a very powerful tool to determine magnitude and distance dependence of tip-sample interactions. It has been used to quantify short-ranged chemical interactions [1] and to identify atomic species [2]. Recording three-dimensional spectroscopy maps [3] are nowadays common practice to determine the tip-sample interaction energy as well as vertical and lateral force fields (see Chap. 2 of this book). After it became possible to image magnetic structures with atomic resolution on insulators [4,18] as well as on metals [5], this technique was also employed to obtain more quantitative information about the short range magnetic tip-sample interaction [6,18]. Noteworthy, such quantitative data can become also relevant for spin-polarized scanning tunneling microscopy (SP-STM) and spectroscopy (SP-STS) experiments, if the tip gets very close to the sample, i.e., during conductance [7] or spin-friction experiments [8]. Moreover, the onset of a Kondo peak splitting has been attributed to the magnetic exchange interaction between a magnetic STM

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Subatomic-scale force vector mapping above a Ge(001) dimer using bimodal atomic force microscopy

et al. 2017

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Probing physical quantities on the nanoscale that have directionality, such as magnetic moments, electric dipoles, or the force response of a surface, is essential for characterizing functionalized materials for nanotechnological device applications [1][2][3] . Currently, such physical quantities are usually experimentally obtained as scalars. To investigate the physical properties of a surface on the nanoscale in depth, these properties must be measured as vectors. Here we demonstrate a three-force-component detection method, based on multifrequency atomic force microscopy on the subatomic scale [4][5][6][7][8][9] and apply it to a Ge(001)-c(4 × 2) surface. We probed the surface-normal and surface-parallel force components above the surface and their direction-dependent anisotropy and expressed them as a three-dimensional force vector distribution. Access to the atomic-scale force distribution on the surface will enable better understanding of nanoscale surface morphologies, chemical composition and reactions 10,11 , probing nanostructures via atomic or molecular manipulation 12,13 , and provide insights into the behaviour of nano-machines on substrates 14,15 . Noncontact atomic force microscopy (AFM) is an excellent tool not only for characterizing the atomic order on a surface but also for detecting the exchange, electrostatic, and chemical force interactions between the AFM tip and the sample surface [16][17][18][19] . However, the conventional AFM, in which the force sensor oscillates perpendicular to the surface, reflects only the surface-normal component of the tip force and ignores the surface-parallel components. Although the parallel component of force has been calculated from the normal component using a potential mapping extraction technique, this method is only indirect [20][21][22][23][24] . To obtain the distribution of the parallel components in three-dimensions (3D) with a higher accuracy, the force sensor should be oscillated also in the direction parallel to the surface 25,26 . Recently, a multi-frequency AFM method was developed 4 with the quest to investigate the physical properties of materials in deeper detail 5,6 . This method utilizes both flexural and torsional modes of the cantilever, thereby making it useful for determining the force in a vector form by allowing the surface-normal (Z direction) and one of the surface-parallel force components (along the X or Y direction) to be simultaneously measured 9 . Here we propose to detect all three components (X , Y and Z) of the total tip-surface force. For that purpose we use a clean Ge(001) surface. The surface has alternately aligned buckling dimers that form an anisotropic c(4 × 2) structure even at room temperature 19 .As shown in Fig. 1, this surface has a structure wherein two domains are separated by a single step; across this step, the dimers are at an angle of 90• to each other. Therefore, both X and Y surface-parallel components of the tip-surface interaction can be obtained from both domains without the need to rotate the tip or t...

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Probing the Magnetic Exchange Forces of Iron on the Atomic Scale

Cited by 49 publications

References 22 publications

Role of tip size, orientation, and structural relaxations in first-principles studies of magnetic exchange force microscopy and spin-polarized scanning tunneling microscopy

Role of tip size, orientation, and structural relaxations in first-principles studies of magnetic exchange force microscopy and spin-polarized scanning tunneling microscopy

Magnetic Exchange Force Spectroscopy

Subatomic-scale force vector mapping above a Ge(001) dimer using bimodal atomic force microscopy

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