{"responseHeader":{"status":0,"QTime":11,"params":{"q":"{!q.op=AND}id:\"703544\"","hl":"true","hl.simple.post":"","hl.fragsize":"5000","fq":"!embargo_tdt:[NOW TO *]","hl.fl":"ocr_t","hl.method":"unified","wt":"json","hl.simple.pre":""}},"response":{"numFound":1,"start":0,"docs":[{"volume_t":"151","date_modified_t":"2009-12-04","ark_t":"ark:/87278/s6rn3s2f","date_digital_t":"2009-10-15","doi_t":"10.1103/PhysRev.151.278","setname_s":"ir_uspace","subject_t":"Magnetic metals","restricted_i":0,"department_t":"Physics","format_medium_t":"application/pdf","creator_t":"Mattis, Daniel C.","identifier_t":"ir-main,8264","date_t":"1966-11","bibliographic_citation_t":"Mattis, D. C. (1966). Anomaly in spin-wave spectrum of magnetic metals. Physical Review, 151(1), 278-9.","mass_i":1515011812,"publisher_t":"American Physical Society","description_t":"It is pointed out that in the band theory of magnetism the magnons have frequencies comparable to the Fermi energy. Therefore, in the calculation of the magnon spectrum of iron, nickel, cobalt, etc., it is the time- or frequency-dependent response function of the electrons which is used, and this function-in contrast with the static response function-does not have a \"Kohn kink\" at q=2ĸғ.","first_page_t":"278","rights_management_t":"(c) American Physical Society http://dx.doi.org/10.1103/PhysRev.151.278.","title_t":"Anomaly in spin-wave spectrum of magnetic metals","journal_title_t":"Physical Review","id":703544,"publication_type_t":"Journal Article","parent_i":0,"type_t":"Text","subject_lcsh_t":"Magnetism, Band theory of; Magnons; Spin waves; Metals -- Magnetic properties","thumb_s":"/ea/bf/eabf94e9b43e245e0cae49ae3994e33c98cce37c.jpg","last_page_t":"279","oldid_t":"uspace 1344","metadata_cataloger_t":"CLR; KWR","format_t":"application/pdf","modified_tdt":"2012-06-13T00:00:00Z","school_or_college_t":"College of Science","language_t":"eng","issue_t":"1","file_s":"/ae/49/ae4944369d6d00521d080fb081a859f351837d78.pdf","format_extent_t":"233,549 bytes","citatation_issn_t":"0031-899X","created_tdt":"2012-06-13T00:00:00Z","_version_":1664094536305999872,"ocr_t":"PHYSICAL REVIEW VOLUME 151, NUMBER 1 4 NOVEMBER 1966 Anomaly in Spin-Wave Spectrum of Magnetic Metals DANIEL C. MATTIs* Belfer Graduate School of Science, Yeshiva University, New York, New York (Received 11 March 1966; revised manuscript received 9 May 1966) It is pointed out that in the band theory of magnetism the magnons have frequencies comparable to the Fermi energy. Therefore, in the calculation of the magnon spectrum of iron, nickel, cobalt, etc., it is the time- or frequency-dependent response function of the electrons which is used, and this function-in contrast with the static response function-does not have a \"Kohn kink\" at q=2kp. But it is found that in the intermediate-coupling regime (exchange force in the range Ep to !Ep) the magnons have a small range of momenta near q=kp where their velocities may be zero or negative, and it is shown how this part of the spectrum may be easily calculated, or approximated analytically. T He present paper draws attention to a possible range of negative magnon velocities in some band-theoretic ferromagnets. The work was initially motivated by an article of Frikkee and Riste,l who found what seemed to them evidence for a Kohn anomaly2 in the spin-wave spectrum of ferromagnetic 3d transitionseries metals. Their experiment consisted of inelastic neutron scattering on an alloy, Co(91%)Fe(9%), the data indicating a break at magnon wave vectors of magnitude approximately qo= O.07X27f/a. (1) Although the experimenters state that (1) is related to the diameter of the Fermi surface (FS), they do not attempt to extract the size or shape of the latter from the experiment because of various uncertainties and ambiguities. Later work seems to have cleared up some of the difficulties; in private communication to the present author, Frikkee states that a plausible explanation for their results now requires invoking the Fermi wave vectors of the 4s electrons, and this may well be the case. As we shall discuss below, a simple model of the 3d magnetic electrons simply cannot lead to a \"Kohn kink\" in the magnon spectrum (a region of infinite group velocity) but may, under the proper circumstances, predict a small region of zero and negative group velocity of the magnon spectrum. At first, we though t this was an explana tion of the above experiment. At the present time, it no longer appears that the two are related. But it would be of interest if such a region of zero and negative group velocity were experimentally discovered in one of the transition ferromagnets, as a senstitive experimental test of some aspects of the band theory of ferromagnetism. We shall find that in the intermediate-coupling regime only (Stoner gap-parameter in the range O.9SEF tEF there is again no maximum, and the magnon frequency w(q) is a monotonically increasing function of q until such point as it merges with the continuum and disappears. The results (2) and (4) taken together imply ql is always less than k F • They are obtained by studying the equations for the magnon energy9: 2kFqh2/3mA=L(Q) , (5) where (h2q2 ) Q=kFqh2/m A+ 2m -hw(q) , (6) and L(Q)=Q-L!(Q-Ll) In 1-1+QI . 1-Q (7) These are the equations appropriate to A?- EF • Using (5) and (6) we obtain the magnon energy and velocity in forms more suitable for analysis: hw(q) = A{1-3L(Q)/2Q+9L2(Q)A/16EF} , (8) and dw hkF v(q)=-=-{ -Q-l+L/Q2L'+3AL/4EF } , (9) dq m where L'=aL/aQ. The point where the magnons merge with the continuum corresponds to Q= 1, hence L= 1 by Eq. (7). Insertion into (5) gives q=0.75 kFA/EF as the wave vector, and hw(q) = (9A!16EF-!)A as the energy of this point. Magnons below the continuum have Q< 1. We may calculate the negative region of (9) to lowest order in (l-Q), as it will be very close to where the magnons merge with the continuum. Thus Q~L~l, but L'~ln(2/1-Q). Thus the negativevelocity range is approximately given by 1>Q>1-2 exp[-( 4EF)] (10) 4EF-3A for any value of the Stoner gap parameter in the range (4). The absence of negative velocities in strong- or weak-coupling means that in the event it is experimentally observed, this phenomenon would approximately determine the coupling constant. We thank Dr. Frikkee for illuminating correspondence. coupling tJ.5:,EF (for tJ.>EF, see the subsequent correct discussion in D. Mattis, Bull. Am. Phys. Soc. 9, 559 (1964), and also Ref. 9, pp. 211-218). 9 D. Mattis, in The Theory of Magnetism (Harper and Row, New York, 1965), p. 215."}]},"highlighting":{"703544":{"ocr_t":[]}}}