Magnetic Scattering in Ni Wires Fabricated on Ferroelectric LiNbO3 Substrate for Magnetic Sensor Application

Abstract

We investigated the magnetoresistive property of a micrometer-scale Ni wire with a uniaxial magnetic anisotropy induced by the formation of a heterojunction between a Ni layer and a single-crystal lithium niobate (LiNbO 3) substrate. We revealed that the domain structure can be controlled by adjusting the wire alignment and that its magnetoresistance (MR) is dependent on the magnetic domain structure as well as the reversal process. The introduction of a heterojunction is a crucial method of controlling the magnetic domain structure owing to the additional generation of the magnetic anisotropy. This control of the magnetic domain structure is very useful for investigating the fundamental physical mechanism and producing artificial multiferroic functional materials and devices. The relatively large MR response observed in transport measurements alludes to the possibility that the spin-dependent scattering mechanism occurs in the domain and domain wall.

X-ray Photoemission Spectroscopy Study of Uniaxial Magnetic Anisotropy Induced in a Ni Layer Deposited on a LiNbO3 Substrate

“…We found that uniaxial magnetic anisotropy was induced in the Ni layer on the LiNbO 3 substrate due to the formation of the heterojunction; the uniaxial magnetic anisotropy forced the Ni magnetizations to stochastically align parallel or antiparallel to the X -axis of the LiNbO 3 substrate (indicated by an arrow in region (i) of Figure 1 b). As previously reported [ 33 , 34 , 35 , 36 , 37 , 38 ], a stripe domain structure is naturally formed when the wire is aligned perpendicular to the X -axis of the LiNbO 3 substrate, even in the absence of an external magnetic field, due to the competition between magnetic shape anisotropy and uniaxial magnetic anisotropy induced by the heterojunction (region (ii) of Figure 1 b) [ 33 , 34 , 35 , 36 , 37 , 38 ]. The magnetic domain width is dependent on the width of wire, being almost equal to the width of the wire.…”

“…The drastic change in the magnetoresistance effect of the Ni wires elongated perpendicular and parallel to the X -axis of the LiNbO 3 substrate, as shown in Figure 4 of Ref. [ 36 ], reflected the unusual domain structures, as observed in Figure 1 .…”

“…In artificial multilayer systems, exchange bias or synthetic antiferromagnetic coupling, which is derived from the quantum interference generated via the heterojunction between ferromagnetic and antiferromagnetic layers, is generally used to control the magnetic properties [ 7 , 8 , 10 , 11 , 12 , 13 , 14 , 15 , 16 , 17 , 18 ]. As for the uniaxial magnetic anisotropy that arises from the heterojunction, some investigations have been reported in the systems consisting of a thin ferromagnetic layer and a ferroelectric substrate, e.g., lithium niobate (LiNbO 3 ) [ 31 , 32 , 33 , 34 , 35 , 36 , 37 , 38 , 39 ]. Several of our previous studies have examined unusual magnetic characteristics found in a 30 nm thick Ni wire fabricated on a single crystal Y-cut 128° LiNbO 3 substrate [ 33 , 34 , 35 , 36 ].…”

“…As for the uniaxial magnetic anisotropy that arises from the heterojunction, some investigations have been reported in the systems consisting of a thin ferromagnetic layer and a ferroelectric substrate, e.g., lithium niobate (LiNbO 3 ) [ 31 , 32 , 33 , 34 , 35 , 36 , 37 , 38 , 39 ]. Several of our previous studies have examined unusual magnetic characteristics found in a 30 nm thick Ni wire fabricated on a single crystal Y-cut 128° LiNbO 3 substrate [ 33 , 34 , 35 , 36 ]. Figure 1 a shows a photoemission electron microscopy (PEEM) topographical image obtained by an ultraviolet lamp, ( Figure 1 b,c) X-ray magnetic circular dichroism photoemission electron microscopy (XMCD-PEEM) images at the Ni L 3 -edge, and ( Figure 1 d) a pair of dichroic X-ray absorption spectra around the Ni L 2,3 -edge of microfabricated 30 nm thick Ni patterns on a LiNbO 3 substrate, obtained at the soft X-ray beam line BL17SU at SPring-8 [ 39 ].…”

Study on relatively large response of rectifying voltage in Ni wires fabricated on a LiNbO3substrate

“…This investigation enabled us to understand the magnetic field dependence of magnetization reversal behavior associated with stripe domain structure formation and domain wall displacement. 16,17,70) To evaluate the magnetism of this system through the electric measurements, a ground-signal-ground-type microwave probe was connected to the CPW electrode. The magnetoresistance (MR) was measured using the lock-in detection technique and the rectifying effect is detected by a bias-tee circuit and a voltmeter as shown in Fig.…”