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Inelastic magnetic neutron scattering with large energy transfers
Journal of Magnetism and Magnetic Materials 52 (1985) 109-110 North-Holland, Amsterdam
INVITED
109
PAPER
INELASTIC M A G N E T I C N E U T R O N SCATI'ERING WITH LARGE ENERGY T R A N S F E R S M. L O E W E N H A U P T Institut fftr Festk6rperforschung, Kernforschungsanlage Ji~lich GmbH, Postfach 1913, D- 5170 J~lich, Fed. Rep. Germany
and C.-K. LOONG Intense Pulsed Neutron Source, Argonne National Laboratory, Argonne, IL 60439, USA
The expectations and limitations of inelastic magnetic neutron scattering experiments with large energy transfers ( > 100 meV) are presented. The state-of-the-art of experiments to measure high energy magnetic excitations in systems containing 3d, 4f and 5f magnetic moments is briefly reviewed and the potential of neutron scattering in this field is discussed. Conventional neutron scattering experiments performed with neutrons from cold and thermal sources have been confined to energy transfers h~0 up to about 100 meV and m o m e n t u m transfers Q up to 10 A - 1 . Being concerned with magnetic neutron scattering there is no need to extend the range of m o m e n t u m transfer to larger Q values. On the contrary, the decrease of the magnetic formfactor (and hence of the scattering intensity) with increasing m o m e n t u m transfer requires Q_< 4 - 6 ,~ ~ to detect magnetic scattering. To enable experiments with larger energy transfers, however, new sources are required which offer a larger amount of high energy neutrons in the eV region. This is accomplished by the hot source of the ILL reactor in Grenoble and by the advance of pulsed spallation neutron sources ( K E N S at KEK, Japan; IPNS at A N L and W N R at LANL, USA; SNS at RAL, UK). An estimate for the extension of the range of energy transfer in magnetic neutron scattering using these new sources is given in fig. 1. Details of the considerations (including the kinematics of the scattering process, background conditions, etc.) are given elsewhere [1,2]. In total, we expect an increase of measureable energy transfers by roughly one order of magnitude as compared to conventional magnetic neutron scattering to about h~0 --- 1 eV. This will allow measurements of X " ( Q , h~o) including (i) spin waves and Stoner excitations in 3d metals; (ii) crystal field levels and spin-orbit splittings in rare earths (40 and actinides (5f); (iii) broad excitation spectra in Kondo, mixed valence, heavy fermion and spin fluctuation systems. 0304-8853/85/$03.30 © Elsevier Science Publishers B.V. (North-Holland Physics Publishing Division)
The use of polarized neutrons and polarization analysis is highly desirable in order to separate unambiguously magnetic and nuclear scattering. Present experiments, however, suffer from severe intensity problems and have therefore to compromise on energy and m o m e n t u m resolution. The state-of-the-art of experiments to measure high energy magnetic excitations in systems containing 3d, 4f and 5f magnetic moments includes: (a) spin waves in Fe [3] and Ni [4] below T~ with energy transfers up to 160 meV;
(meV 100 100 - ~ / / / / t ~ ~ ~ IC
0.1
'
z" z" !~' .......... 1
10
100 Q ( K 1 ) --'=,"
Fig. 1. Accessible range in energy and momentum transfer in conventional neutron scattering (typical E 0 < 100 meV, hatched area) and magnetic neutron scattering with large energy transfers (assuming a realistic upper bound for E o < 10 eV, crosshatched area). Solid line corresponds to 0 ° scattering angle. A more realistic boundary in the low Q region is indicated by the dashed line.
110
M. Loewenhaupt, C. - K. Loong / Large energy transfer neutron scattering
(b) crystal field excitations a n d spin-orbit splittings in rare earths and actinides [5,6] with energy transfers up to 260 meV; (c) b r o a d quasielastic and inelastic excitations in mixed valence [7] a n d spin fluctuation systems [6]. F o r more details on the above listed topics we refer to the original literature and the references therein.
References [1] M. Loewenhaupt, in: Proc. Conf. on High Energy Excitations in Condensed Matter, Los Alamos, ed. R.A. Silver (1984), Report No. LA-10227-C, vol. 1, p. 315.
[2] M. Loewenhaupt, H. Rauh and V. Wagner, in: Proc. Workshop on Neutron Scattering Instrumentation for SNQ, eds. R. Scherm and H. Stiller, KFA Ji~1-1954 report (October 1984) p. 221. [3] C.-K. Loong, J.M. Carpenter, J.W. Lynn, R.A. Robinson and H.A. Mook, J. Appl. Phys. 55 (1984) 1895. [4] H.A. Mook and D. McPaul, Phys. Rev. Lett. 54 (1985) 227. [5] C.-K. Loong, J. Appl. Phys. 57 (1985) 3772. [6] M. Loewenhaupt, Physica 130B (1985) 347. [7] R.M. Galera, D. Givord, J. Pierre, A.P. Murani, J. Schweizer, C. Vettier and K.R.A. Ziebeck, J. Magn. Magn. Mat. 52 (1985) 103.
INVITED
109
PAPER
INELASTIC M A G N E T I C N E U T R O N SCATI'ERING WITH LARGE ENERGY T R A N S F E R S M. L O E W E N H A U P T Institut fftr Festk6rperforschung, Kernforschungsanlage Ji~lich GmbH, Postfach 1913, D- 5170 J~lich, Fed. Rep. Germany
and C.-K. LOONG Intense Pulsed Neutron Source, Argonne National Laboratory, Argonne, IL 60439, USA
The expectations and limitations of inelastic magnetic neutron scattering experiments with large energy transfers ( > 100 meV) are presented. The state-of-the-art of experiments to measure high energy magnetic excitations in systems containing 3d, 4f and 5f magnetic moments is briefly reviewed and the potential of neutron scattering in this field is discussed. Conventional neutron scattering experiments performed with neutrons from cold and thermal sources have been confined to energy transfers h~0 up to about 100 meV and m o m e n t u m transfers Q up to 10 A - 1 . Being concerned with magnetic neutron scattering there is no need to extend the range of m o m e n t u m transfer to larger Q values. On the contrary, the decrease of the magnetic formfactor (and hence of the scattering intensity) with increasing m o m e n t u m transfer requires Q_< 4 - 6 ,~ ~ to detect magnetic scattering. To enable experiments with larger energy transfers, however, new sources are required which offer a larger amount of high energy neutrons in the eV region. This is accomplished by the hot source of the ILL reactor in Grenoble and by the advance of pulsed spallation neutron sources ( K E N S at KEK, Japan; IPNS at A N L and W N R at LANL, USA; SNS at RAL, UK). An estimate for the extension of the range of energy transfer in magnetic neutron scattering using these new sources is given in fig. 1. Details of the considerations (including the kinematics of the scattering process, background conditions, etc.) are given elsewhere [1,2]. In total, we expect an increase of measureable energy transfers by roughly one order of magnitude as compared to conventional magnetic neutron scattering to about h~0 --- 1 eV. This will allow measurements of X " ( Q , h~o) including (i) spin waves and Stoner excitations in 3d metals; (ii) crystal field levels and spin-orbit splittings in rare earths (40 and actinides (5f); (iii) broad excitation spectra in Kondo, mixed valence, heavy fermion and spin fluctuation systems. 0304-8853/85/$03.30 © Elsevier Science Publishers B.V. (North-Holland Physics Publishing Division)
The use of polarized neutrons and polarization analysis is highly desirable in order to separate unambiguously magnetic and nuclear scattering. Present experiments, however, suffer from severe intensity problems and have therefore to compromise on energy and m o m e n t u m resolution. The state-of-the-art of experiments to measure high energy magnetic excitations in systems containing 3d, 4f and 5f magnetic moments includes: (a) spin waves in Fe [3] and Ni [4] below T~ with energy transfers up to 160 meV;
(meV 100 100 - ~ / / / / t ~ ~ ~ IC
0.1
'
z" z" !~' .......... 1
10
100 Q ( K 1 ) --'=,"
Fig. 1. Accessible range in energy and momentum transfer in conventional neutron scattering (typical E 0 < 100 meV, hatched area) and magnetic neutron scattering with large energy transfers (assuming a realistic upper bound for E o < 10 eV, crosshatched area). Solid line corresponds to 0 ° scattering angle. A more realistic boundary in the low Q region is indicated by the dashed line.
110
M. Loewenhaupt, C. - K. Loong / Large energy transfer neutron scattering
(b) crystal field excitations a n d spin-orbit splittings in rare earths and actinides [5,6] with energy transfers up to 260 meV; (c) b r o a d quasielastic and inelastic excitations in mixed valence [7] a n d spin fluctuation systems [6]. F o r more details on the above listed topics we refer to the original literature and the references therein.
References [1] M. Loewenhaupt, in: Proc. Conf. on High Energy Excitations in Condensed Matter, Los Alamos, ed. R.A. Silver (1984), Report No. LA-10227-C, vol. 1, p. 315.
[2] M. Loewenhaupt, H. Rauh and V. Wagner, in: Proc. Workshop on Neutron Scattering Instrumentation for SNQ, eds. R. Scherm and H. Stiller, KFA Ji~1-1954 report (October 1984) p. 221. [3] C.-K. Loong, J.M. Carpenter, J.W. Lynn, R.A. Robinson and H.A. Mook, J. Appl. Phys. 55 (1984) 1895. [4] H.A. Mook and D. McPaul, Phys. Rev. Lett. 54 (1985) 227. [5] C.-K. Loong, J. Appl. Phys. 57 (1985) 3772. [6] M. Loewenhaupt, Physica 130B (1985) 347. [7] R.M. Galera, D. Givord, J. Pierre, A.P. Murani, J. Schweizer, C. Vettier and K.R.A. Ziebeck, J. Magn. Magn. Mat. 52 (1985) 103.