Abnormal magnetoresistance behavior in Nb thin films with rectangular arrays of antidots

Abstract

Abstract. Abnormal magnetoresistance behavior is found in superconducting Nb films perforated with rectangular arrays of antidots (holes). Generally magnetoresistance were always found to increase with increasing magnetic field. Here we observed a reversal of this behavior for particular in low temperature or current density. This phenomenon is due to a strong 'caging effect' which interstitial vortices are strongly trapped among pinned multivortices. IntroductionSuperconducting thin films with periodic arrays of pinning sites have received much attention in purposes to enhance critical parameters [1,2,3,4] and artificially control the motion of vortices [5]. When the number of vortices equals to an integer multiple or fractional of the number of pinning centers, dips in resistance or peaks in critical current as a function of the applied magnetic field can be visible, which was known as the commensurate effect or matching effect [1,6]. In Nb thin films with rectangular array of magnetic dots and nonmagnetic dots, interesting phenomena have been revealed, such as the channeling effect [7], anisotropy in critical current [8] and vortex-lattice reconfiguration transition [9,10,11]. When the reconfiguration transition occurred, changes in the shape of the minima and their periodicity in the magnetoresistance curves were found. Two possible models have been proposed to explain this phenomenon: the geometrical reconfiguration model [9], and the multivortex model [11]. However, it's still unclear that the causes of the oscillations in magnetoresistance after the transition. In this paper, to investigate the pinning mechanism in high field regime, we performed transport measurements in rectangular arrays of antidots with different aspect ratios of unit cell. We observed a temperature and current dependent reconfiguration transition. After the transition, a decrease in magnetoresistance was found at high field. This abnormal behavior is accounted for a reduction of the mobility of interstitial vortices by a 'caging effect'. This effect has been predicted by theoretical simulations [12,13].

Angle-dependent spin waves in antidot bilayers

“…[1][2][3][4][5][6][7] Patterning in a film is an easy and effective way of fabricating these devices, which many researches have focused on, with a patterned shape of triangle, dot, square, and so on. [8][9][10] It is interesting to reveal the intrinsic properties of spin waves in patterned structures, owing to the localization of spin waves. This will be very helpful for more applications in magnetic storages with different patterned shapes.…”

Enhanced vortex pinning in Nb using proximity effect through organic molecules

“…Since the density of vortices increases linearly with the magnetic field, a periodic (as a function of applied magnetic field) drop in the magnetoresistance is expected under such commensurate conditions, e.g., whenever integer numbers of the vortex density are equal to the pinning-site density. Numerous methods have been implemented to produce periodic pinning sites by modifying the condensation energy landscapes, including the deposition of arrays of magnetic and non-magnetic dots [15,18] and the establishment of varying film thickness [19], film corrugation [20], anti-dots or holes [21][22][23] and lattice defects [24]. In matching field conditions, the critical current in proximity to the dot is increased [25,26] and the total inter vortex forces are minimized according to the Abrikosov triangular lattice [27].…”