Local tunneling magnetoresistance probed by low-temperature scanning laser microscopy

Abstract

Tunneling magnetoresistance (TMR) in a vertical manganite junction was investigated by lowtemperature scanning laser microscopy (LTSLM) allowing to determine the local relative magnetization M orientation of the two electrodes as a function of magnitude and orientation of the external magnetic field H. Sweeping the field amplitude at fixed orientation revealed magnetic domain nucleation and propagation in the junction electrodes. For the high-resistance state an almost single-domain antiparallel magnetization configuration was achieved, while in the low-resistance state the junction remained in a multidomain state. Calculated resistance R calc (H) based on the local M configuration obtained by LTSLM is in quantitative agreement with R(H) measured by magnetotransport.Tunneling magnetoresistance (TMR) is an important effect for spintronics 1 which has been vigorously investigated both theoretically 2,3 and experimentally 4,5 , predominantly to develop new devices such as magnetic random access memories (MRAMs) 6 based on magnetic tunnel junctions (MTJs). In an MTJ, two ferromagnetic electrodes are separated by a thin insulating tunnel barrier. According to the Jullière model 4 , the maximum TMR ratio is TMR J ≡ (R ap − R p )/R p , where R ap and R p is the resistance for antiparallel and parallel orientation of the magnetizations M of the two electrodes, respectively. While integral TMR properties of MTJs have been investigated in detail 7,8 , not much is known about the impact of their magnetic microstructure on the TMR properties. However, both in view of applications and from a fundamental point of view, it is of high interest to identify the spatial dependence of the TMR on the magnetic properties of the electrodes. Nucleation and growth of magnetic domains in ferromagnets has been the focus of many efforts, using techniques such as magneto-optical Kerr, magnetic force, spin-polarized scanning tunneling, spin-polarized scanning electron and photoemission microscopy. 9 Low-temperature scanning laser microscopy (LTSLM) has been used to visualize locally different resistive states in a quasi-1-dimensional La 0.67 Ca 0.33 MnO 3 thin film grain boundary junction, for which it has been shown that the obtained LTSLM signal is directly proportional to the local TMR ratio. 10 These results suggested that LTSLM could also be useful to investigate TMR in vertical MTJs under typical bias conditions and in a wide range of temperatures and magnetic fields. was investigated in Ref. [11]. LTSLM probes changes in the tunneling conductivity induced by local thermal perturbation, which allows to infer the spatial distribution of the relative magnetization orientation of the two electrodes. By varying H, imaging of magnetic domain nucleation and propagation during the field-driven transitions between low-and high-resistive states is possible.The heterostructure samples were grown in situ by molecular beam epitaxy on (001)-oriented STO substrates with 19 nm thick top and bottom LSMO electrodes, separated by 2.3 nm thick STO. A 38...

A high-resolution combined scanning laser and widefield polarizing microscope for imaging at temperatures from 4 K to 300 K

“…It was shown by Dieckmann et al 69 that this technique, lowtemperature scanning laser microscopy (LTSLM), delivers results that are equivalent to LTSEM. LTSLM has, among others, been applied to research on superconductors 32,34,70,71 , the quantum Hall effect 72 , spintronics 73,74 and spin-caloritronics 75 . The LTSPM can be operated in LTSLM mode to gain information on the electric trans- port properties of a sample.…”

Hot-spot formation in stacks of intrinsic Josephson junctions in Bi2Sr2CaCu2O8

“…[69]. However, if dR c (T )/dT dominates the thermal physics, ∆V (x 0 , y 0 ) can be treated as in [70] yielding…”