Contents lists available at ScienceDirect Journal of Magnetism and Magnetic Materials journal homepage: www.elsevier.com/locate/jmmm Research articles Diameter dependent structural and magnetic properties of CoNi alloy nanotubes S. Parajuli a,b , M. Irfan a,c , X.M. Zhang a,b , K. Javed a,d , J.F. Feng a , X.F. Han a,b, ⁎ a Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China b Centre of Materials Science and Optoelectronics Engineering, University of Chinese Academy of Sciences, Beijing 100049, China c Department of Physics, The Islamia University of Bahawalpur, Bahawalpur 63100, Pakistan d Department of Physics, Forman Christian College (A Chartered University), Lahore 54000, Pakistan ARTICLE INFO Keywords: CoNi NTs Electrodeposition Magnetization reversal mechanism ZFC-FC curve Bloch law ABSTRACT Cobalt-Nickel (CoNi) alloy nanotubes (NTs) with diameters 50 nm (D 1 ), 100 nm (D 2 ), 150 nm (D 3 ), and 200 nm (D 4 ) have been fabricated using Anodic Aluminum Oxide (AAO) membranes. X-ray diffraction spectroscopy (XRD), field-emission scanning electron microscopy (FE-SEM), vibrating-sample magnetometer (VSM), and physical property measurement system (PPMS) analysis methods were employed to systematically investigate the structural, morphological and magnetic properties of CoNi NTs samples. Magnetization reversal mechanism has been explained by angular dependence of coercivity. Low temperature studies have shown that coercivity Hc of nanotubes follows the thermal activation model. Temperature dependence of Hc follows the 3/2 power law for the field dependence of energy barriers. 1. Introduction The areal density has been increased using nanomagnets, in which one bit of information corresponds to a single-domain nanosized par- ticle. One simple and economical way of achieving nanomagnetic ar- rays over a large area is based on well-organized Anodic Aluminum Oxide (AAO) templates. It came into limelight from notable work of Masuda and Fukuda [1], that AAO templates have many benefits over the polycarbonate membranes in terms of high pore density, thermal stability, versatility and cost effectiveness. Therefore, AAO is widely used in the fields of bio-sensors [2,3], and bio-filtrations [4], as nano- templates [5], for the fabrication of secondary nanostructured mate- rials. Several methods have been applied to fill the pores of AAO tem- plate with metallic and magnetic nanostructures examples such as solgel [6,7], electrochemical deposition [8–12] electrolysis deposition [13],and chemical vapor deposition [14]. Electrochemical deposition is the most common route because of its simple, efficient, multipurpose, and economical technique, and its considerable control over composi- tion and growth. Anodization of metals is always associated with an insulating barrier layer between the metal substrate and metal oxide film. The insulting properties of the barrier layer have significant effect on the uniformity and quality of the depositing material [15]. There- fore, handling of the barrier layer during deposition of secondary ma- terial in the nanopores of AAO is indispensable. One-dimensional (1D) metallic nanostructures such as nanowires, nanorods, and nanotubes (NTs) play a distinctive role in the field of nanoworld due to their high aspect ratio (length/diameter) and large surface area. Owing to prospective application in the fields of ultra-high density magnetic storage, magneto-electronics, high sensitive giant magneto resistance (GMR) sensors [16] and wide variety of materials and configuration of core shell [17], multilayered [18], etc., which is an excellent candidate to engineer magnetic domain structures. Ferro- magnetic (Fe, Co, Ni) NTs have got a lot of attention in recent decades. Nickel (Ni) is frequently used for electrodeposition due to its excellent mechanical properties. However, Ni is not mechanically hard enough for certain purpose so which demand high strength and low wear rate. That’s why electrodepositing Ni with cobalt (Co) results as alloy. Fur- thermore, CoNi ferromagnetic alloys having high mechanical strength [19], good wear resistance [20], anti-corrosive performance [21], and electro catalytic activity [22] have been extensively used in the elec- tronic, magnetic, electric, mechanical, petrochemical and medical fields. Various magnetic metal NTs have been fabricated using AAO template-based electrochemical deposition, but few reports on Co-Ni alloy NTs are available. Although intensive research has been done for understanding the magnetic properties of various ferromagnetic NTs in terms of coercivity and remanence, till date, research on the shape of hysteresis loops related to the magnetization configuration in ferro- magnetic NTs has almost been neglected. So, in this paper, we have https://doi.org/10.1016/j.jmmm.2019.166264 Received 23 September 2019; Received in revised form 20 November 2019; Accepted 2 December 2019 ⁎ Corresponding author at: Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China. E-mail address: xfhan@iphy.ac.cn (X.F. Han). Journal of Magnetism and Magnetic Materials 500 (2020) 166264 Available online 14 December 2019 0304-8853/ © 2019 Elsevier B.V. All rights reserved. T