Stability of spinmotive force in perpendicularly magnetized nanowires under high magnetic fields

Abstract

Spinmotive force induced by domain wall motion in perpendicularly magnetized nanowires is numerically demonstrated. We show that using nanowires with large magnetic anisotropy can lead to a high stability of spinmotive force under strong magnetic fields. We observe spinmotive force in the order of tens of µV in a multilayered Co/Ni nanowire and in the order of several hundred µV in a L10-ordered FePt nanowire; the latter is two orders of magnitude greater than that in permalloy nanowires reported previously. The narrow structure and low mobility of a domain wall under magnetic fields in perpendicularly magnetized nanowires permits downsizing of spinmotive force devices.The mutual interaction between spin current and magnetization is a key phenomenon in the field of spintronics [1]. Spin current induces magnetization dynamics, i.e., spin-transfer-torque [2][3][4][5], which has been extensively studied through current-induced domain wall (DW) motion, primarily in permalloy (NiFe) nanowires with in-plane magnetization [6][7][8][9][10]. Recently, it has been reported experimentally [11,12] and theoretically [13,14] that nanowires with perpendicular magnetic anisotropy (PMA) are more favorable for spin-transfer-torque devices because they exhibit DW motion at a lower threshold current. On the other hand, the same interaction mediates energy-transfer from magnetization into conduction electrons, i.e., spinmotive force (SMF) [15]. Like the spin-transfer-torque [16] and other spin-related electromotive forces [17,18], SMF offers a promising functionality for future spintronic devices; e.g., it can be used to read out magnetic information [19]. SMF has been primarily demonstrated in NiFe [20][21][22][23][24][25], and only few reports have demonstrated SMF in PMA materials [26]. However, the soft magnetic properties of NiFe could occasionally be a major disadvantage for an SMF demonstration; certain magnetization structures are easily disturbed by a strong magnetic field, leading to an increased instability in SMF signals. Therefore, SMF induced by DW motion in NiFe nanowires is limited to a few µV [20,25].In this paper, the SMF induced by DW motion in PMA nanowires is numerically investigated. The abovementioned problem in the NiFe nanowires is resolved by using PMA nanowires, which show rigid DW motion because of their high magnetic anisotropy. It has been shown that materials with the high PMA are effective in achieving a large SMF. We numerically observe SMF in the order of tens of µV in a multilayered Co/Ni nanowire and in the order of several hundred µV in a L1 0 -ordered FePt nanowire with the very large PMA. In addition, the narrow structure and low mobility of a DW in PMA nanowires are effective in downsizing of devices using SMF.Let us begin by assessing SMF induced by DW motion in NiFe nanowires. It has been pointed out that SMF is generally produced by the spin electric field[27-31];where m is the unit vector parallel to the direction of local magnetization of the ferromagnet, P is the average spin polarizatio...

Spin Current: Experimental and Theoretical Aspects

“…Fueled by the verification of the prediction by Barnes and Maekawa, the concept of the SMF has attracted researchers, and there has been some progress in both experiment [75][76][77][78][79] and theory. [107][108][109][110][111][112][113][114][115][116][117][118] In 2011, Yamane et al provided a new formalism of SMF, where the equation of motion of a conduction electron is studied, as will be detailed in the following. If one knows f AE , the induced SMF is calculated in the same way as in the classical electromagnetism, where the inductive electromotive force is induced by f e .…”

Nanostructure-induced L10-ordering of twinned single-crystals in CoPt ferromagnetic nanowires

“…Ferromagnetic nanowires have great potential for ultrahighdensity data storage applications, such as magnetic domainwall racetrack memory and perpendicular magnetic recording, [1][2][3][4][5][6][7][8][9] as well as for spintronic sensors, [10][11][12][13][14][15][16][17] spin torque oscillators, 18,19 excitation of spin waves, 20,21 spinmotive force devices, 22,23 and biomedical applications. 24,25 In magnetic domain-wall racetrack memory, magnetic domains in an array of ferromagnetic nanowires store the data.…”

Spinmotive Force as a New Energy Conversion Mechanism

“…We have resolved this difficulty in the NiFe nanowires by considering the materials choice; by using perpendicular magnetic anisotropy (PMA) materials (hard magnets), we have shown that rigid DW motion is achieved, and hence, the associated SMF signals can be stabilized 9) . We have numerically confirmed that SMFs in the order of tens of µV in a multilayered Co/Ni nanowire and in the order of several hundreds of µV in an L10-ordered FePt nanowire with the very large PMA can be obtained.…”