IEEE TRANSACTIONS ON MAGNETICS, VOL. 45, NO. 10, OCTOBER 2009 4015 Effect of Temperature on the Ferromagnetic-Resonance Field and Line Width of Epitaxial Fe Thin Films Bijoy K. Kuanr , V. Veerakumar , Alka V. Kuanr , R. E. Camley ,and Z. Celinski Center for Magnetism and Magnetic Nanostructures, Department of Physics, University of Colorado at Colorado Springs, Colorado Springs, CO 80918 USA Rajguru College of Applied Science for Women, Jhilmil Colony, Vivek Vihar, Delhi-110 092, India The temperature dependence of the ferromagnetic-resonance field and line width of epitaxial Fe thin films were studied. It is observed that increases whereas decreases with the increase in temperature. The change in is governed by the temperature dependence of the saturation magnetization and the magneto-crystalline anisotropy energy of the film. The present low- temperature investigations of obeys the well-known Bloch law. The resonance line width as a function of temperature shows a transition temperature separating two different regimes. This behavior may be associated with the temperature dependence of the anistropy. The results are confirmed theoretically by simulating the power absorbed at ferromagnetic resonance by using the Landau–Lifsthiz–Gilbert equation. Index Terms—Fe thin film, ferromagnetic resonance, magnetic thin films. I. INTRODUCTION W ITH the rapid progress of nanotechnology and high-density recording, there is great interest in studying magnetization dynamics in magnetic nanostruc- tures. Ferromagnetic thin films and metallic multilayers have been the subject of intensive work during the last decades [1]–[10]. Epitaxial growth of magnetic layers on semicon- ductor substrates has been widely attempted for the integration of magnetic/semiconductor hybrid devices [1]–[3]. One of the major issues in the magnetic data-storage industry is the data-transfer rate. Frequencies for writing and reading are now in the microwave region, which raises the question, “How fast can magnetic materials switch?” The answer is determined in part by the relaxation mechanisms in the magnetic film [3]–[7]. In addition, the anisotropy field of the epitaxial Fe system can act as an internal field that can boost the resonance frequency of microwave bandpass/bandstop filters at the zero applied magnetic field [4], [5]. The interfaces play an important role in these structures. It has been reported that for Fe films deposited directly on gal- lium-arsenide (GaAs) substrates at high temperature, interdif- fusion of As species into the upper iron layer could occur. The resulting compound forms a magnetically dead layer at the interface, which can severely degrade the magnetization of the sample and leads to a disruptive effect at the semiconductor/ metal interface. The fundamental magnetic, electronic, and op- tical properties of ultra-thin film structures can be quite dif- ferent from their bulk counterparts. In addition, the magnetic parameters of thin films are highly affected by growth condi- tions, sample treatment, purity of the alloys, temperature, etc. One of the most interesting questions on this subject is the de- pendence of the magnetic anisotropies with temperature [2]. In Manuscript received March 07, 2009; revised April 30, 2009. Current ver- sion published September 18, 2009. Corresponding author: B. K. Kuanr (e-mail: bkkuanr@yahoo.com). Color versions of one or more of the figures in this paper are available online at http://ieeexplore.ieee.org. Digital Object Identifier 10.1109/TMAG.2009.2023231 this context, Fe has been one of the most extensively used ma- terials for studying magnetic properties of ferromagnetic thin films [6]–[11]. In this paper, we present ferromagnetic-resonance (FMR) measurements on single crystal Fe films grown on the GaAs(001)/Fe(1 nm)/Ag(150 nm) template as a function of temperature between 20 and 300 K. Experimental and theo- retical studies of the resonance field and resonance line width were performed at different temperatures. Also, the inplane angle dependence of was performed at different temperatures. The model assumes that the observed temperature variations of resonance field and line width are due to the temperature dependence of the anisotropy and magnetization. II. EXPERIMENT The experiments were carried out on samples with the fol- lowing principal structure: GaAs(001) substrate, 1-nm Fe seed layer, 150–nm Ag layer, principal Fe films 16 and 6 nm, and the 500-nm ZnS layer [1]. A GaAs(001)/Fe(1 nm)/Ag(150 nm) template was chosen for epitaxial growth of the principal Fe film. The films were grown by molecular-beam-epitaxy at a background pressure of Torr and at a deposition rate of 0.01 nm/s. The recipe of epitaxial growth is given elsewhere [1]. In-situ characteriza- tion is performed by Auger electron spectroscopy, low-energy electron diffraction (LEED), and reflection high-energy electron diffraction (RHEED). Both RHEED and LEED indicated the epitaxial growth of Fe. Room temperature magneto-optic Kerr effect (MOKE) measurements were performed. The coercivity of the Fe films was determined by MOKE hysteresis loops (Fig. 1) and is found to be 8 Oe. The analysis of the easy and hard-axis MOKE graphs gives the cubic anisotropy for the 16-nm Fe sample as 610 Oe. Conventional FMR investigations at 24 GHz were performed with an FMR spectrometer using the field-modulation tech- nique. The temperatures were measured using the resistance thermometer. Low-temperature measurements were performed by using a closed-cycle helium Dewar system at a vacuum of 0018-9464/$26.00 © 2009 IEEE