e117601 - 01(2007 PHYSICAL REVIEW LETTERS week ending 16...

Info iconThis preview shows pages 1–2. Sign up to view the full content.

View Full Document Right Arrow Icon
Low Relaxation Rate in Epitaxial Vanadium-Doped Ultrathin Iron Films C. Scheck, 1 L. Cheng, 1 I. Barsukov, 2 Z. Frait, 2 and W. E. Bailey 1, * 1 Materials Science, Department of Applied Physics and Applied Mathematics, Columbia University, New York, New York 10027, USA 2 Institute of Physics, Academy of Sciences of the Czech Republic, Prague, Czech Republic (Received 29 December 2006; published 12 March 2007) The longest relaxation time and sharpest frequency content in ferromagnetic precession is determined by the intrinsic (Gilbert) relaxation rate G . For many years, pure iron (Fe) has had the lowest known value of G ± 57 MHz for all pure ferromagnetic metals or binary alloys. We show that an epitaxial iron alloy with vanadium (V) possesses values of G which are signi±cantly reduced to 35 ² 5 MHz at 27% V. The result can be understood as the role of spin-orbit coupling in generating relaxation, reduced through the atomic number Z . DOI: 10.1103/PhysRevLett.98.117601 PACS numbers: 76.30.Fc, 72.25.Rb, 75.40.Gb, 75.50.Bb Ultrafast magnetization dynamics comprise a major area of current research in magnetism. Novel dynamical phe- nomena have been observed recently in con±ned structures [ 1 ], with programmed ±eld pulses [ 2 , 3 ], through interac- tions with intense light pulses [ 4 , 5 ], and under the in²u- ence of spin polarized currents [ 6 , 7 ]. In all cases, the observed phenomena compete against ferromagnetic relaxation in the magnetic material. Relaxation aligns magnetization M with applied ±elds H , bringing dynamics to a stop. The lowest limit of the relaxation rate is intrinsic to a given material and given by G ± ±²M s , where ² is the related dimensionless damping constant. In metals, the damping has seen renewed theo- retical interest [ 8 ] motivated particularly by its formal relationship with spin momentum transfer torques [ 9 , 10 ], or by its enhancement with impurities [ 11 ]. Low relaxation rates are of particular interest for low critical currents in spin momentum transfer [ 12 ], narrow band response in frequency domain devices [ 13 ], and reduced thermal noise in nanoscale magnetoresistive sensors [ 14 ]. Pure iron (Fe) has long been known to exhibit the lowest measured intrinsic relaxation rate of all elemental ferro- magnetic metals or binary alloys [ 15 ]. Lowest values of 57 MHz ( ² ± 0 : 002 ) have been found in both single- crystal whiskers and epitaxial ±lms [ 16 ] at room tempera- ture. Elemental Ni, Co, and standard alloys such as Ni 81 Fe 19 show much higher values ( G ± 220 , 170, 114 ² 10 MHz , respectively.) In this Letter, we show that the intrinsic relaxation rate G in a low- Z ferromagnetic alloy can be substantially lower than that known for pure Fe. Epitaxial MgO ³ 100 ´ = Fe 1 ÿ x V x ³ 8nm ´³ 100 ´ ultrathin ±lms, deposited by UHV sputtering, exhibit values of G to 35 MHz, reduced by µ 40% . While a comparable value has been identi±ed recently in NiMnSb [ 7 ], the low damping has been attrib- uted to the special electronic characteristics of this ordered, half -metallic compound [ 17 ], including a low orbital com- ponent of the magnetic moment. We show that in Fe 1 ÿ x V x
Background image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full DocumentRight Arrow Icon
Image of page 2
This is the end of the preview. Sign up to access the rest of the document.

This note was uploaded on 03/05/2010 for the course PHYS qf taught by Professor Mitra during the Spring '10 term at Aarhus Universitet.

Page1 / 4

e117601 - 01(2007 PHYSICAL REVIEW LETTERS week ending 16...

This preview shows document pages 1 - 2. Sign up to view the full document.

View Full Document Right Arrow Icon
Ask a homework question - tutors are online