Epitaxial growth, structure, and magnetism of epitaxial Ni 80 Fe 20 single-crystal, bicrystal, and quad-crystal films J. C. A. Huang, 1,2, * C. C. Yu, 2 C. M. Fu, 3 and C. H. Lee 4 1 Physics Department, National Cheng-Kung University, Tainan, Taiwan 2 Institute of Physics, Academia Sinica, Taipei, Taiwan 3 Department of Physics, National Kaohsiung Normal University, Kaohsiung, Taiwan 4 Department of Engineering and System Science, National Tsing-Hua University, Hsinchu, Taiwan Received 4 May 2001; published 15 October 2001 The structure and magnetism of epitaxial Ni 80 Fe 20 films grown on stepped and nonstepped Mo001 planes and MgO110 substrate have been studied. Single-crystal Ni 80 Fe 20 110 films were prepared on MgO110 substrates. Bi-crystal Ni 80 Fe 20 110 films were stabilized on Mo001 nonstepped planes. On Mo001 stepped surfaces, interestingly enough, quad-crystal Ni 80 Fe 20 110 films with rough surfaces were formed above 200 °C and single-crystal Ni 80 Fe 20 001 films with smooth surfaces were formed below 100 °C. Thick films 300 Å of single-crystal, bicrystal, and quad-crystal Ni 80 Fe 20 110 show uniaxial, biaxial and isotropic magnetic behavior, respectively. The easy axis of the single-crystal Ni 80 Fe 20 001 is directed along the Mo step edge direction and the M-H loop along the hard axis reveals a two-step magnetic moment rotation process. The magnetic anisotropies of the Ni 80 Fe 20 films were determined by vibrating sample magnetometer. Details of the epitaxial growth and interplay of structure and magnetism of these Ni 80 Fe 20 films are presented. DOI: 10.1103/PhysRevB.64.174422 PACS numbers: 75.70.Ak, 68.55.Jk, 75.50.Bb I. INTRODUCTION Permalloy (Py=Ni 80 Fe 20 ) has been studied for years both for basic research and technological applications. 1 In the re- cent years, Py-related multilayers 2 and spin-valve heterostructures 3,4 have attracted much attention thanks to the discovery of the giant magnetoresistance effect with low saturation field, which can be applied for advanced magnetic sensors such as the read head of a hard disk. Understanding and control of the structure and magnetism of Py films is thus of importance. Most of the previous studies on Py films have been re- stricted to textured or polycrystal samples, making the un- derstanding of the structural and magnetic properties and their interplay very difficult. In this article we report the molecular beam epitaxy MBE growth and structural and magnetic characterizations of high-quality single-crystal, bi- crystal, and quad-crystal Py films. Particularly, we found an interesting phenomenon that Py films grow as distinct crystal structures on Mo100 stepped and nonstepped surfaces, which in turn results in different magnetic anisotropies in these two cases. Details of the MBE growth, structure, and magnetism of these Ni 80 Fe 20 films are presented. This paper is organized as follows. First, we describe the experimental procedures of preparation of single-crystal, bi- crystal, and quad-crystal Py films by the MBE technique. Details of the crystal and surface properties of these epitaxial Py films are then reported. Magnetic properties and the in- terplay between the structure and magnetism of the Py films are presented before the conclusion is made. II. SAMPLE PREPARATION AND MEASUREMENTS The crystal growth was carried out in a MBE system Vacuum Product made, MBE-930 with a base pressure of about 5 10 -10 torr. This MBE chamber allowed sample transfer under UHV conditions to an analysis chamber for further antiferromagnetic scanning tunneling microscopy AFM-STM study. 5,6 Mo001 stepped and nonstepped seeding templates were prepared on epitaxial-grade Al 2 O 3 1-102 and MgO100 substrates, respectively. Py films were simultaneously grown on the Mo001 stepped and nonstepped seeding templates. The growth pressure of the Permalloy layer was controlled below 3 10 -9 torr, and the deposition rate at 0.1 Å/s. For comparison, we also directly prepared Py films on MgO110 substrate. The surface structure and morphology of the Py films were characterized by reflection high-energy electron diffrac- tion RHEED and atomic force microscopy AFM. The crystal quality was also analyzed by x-ray diffraction XRD. The angular-dependent longitudinal magneto-optical Kerr ef- fect LMOKE and vibration sample magnetometer VSM were employed to study the correlation of the magnetism and crystal structure of the Py films. III. EPITAXIAL GROWTH AND STRUCTURE CHARACTERIZATIONS A. Py„110… single crystal on MgO„110… For convenience of discussion of bicrystal and quad- crystal structures in the following sections, we first present the MBE growth single-crystal Py110 films. The Py110 single crystal can be formed by deposition of Py directly on MgO110 substrate. In this case, we have obtained the simple orientation relations from XRD and RHEED studies: Py 110  MgO 110 , Py 001  MgO 001 , Py 1 -10  MgO 1-10 . PHYSICAL REVIEW B, VOLUME 64, 174422 0163-1829/2001/6417/1744229/$20.00 ©2001 The American Physical Society 64 174422-1