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Manganese hyperfine interaction in intermetallic Mn compounds
Journal of Magnetism and Magnetic Materials 226}230 (2001) 1188}1189
Manganese hyper"ne interaction in intermetallic Mn compounds M.T. Kelemen, Ch. SuK rgers, E. Dormann* Physikalisches Institut, Universita( t Karlsruhe, D-76128 Karlsruhe, Germany
Abstract Local manganese moments at di!erent lattice sites in intermetallic Mn compounds can be derived by analysis of the Mn nuclear magnetic resonance (NMR) spectra. This was used for Gd Y Mn Ge pseudoternary compounds and V \V Mn Si C "lms. Careful NMR line shape analysis also yields anisotropic hyper"ne and quadrupole interaction pointing to weak but non-negligible orbital moments. 2001 Elsevier Science B.V. All rights reserved. Keywords: NMR; Manganese; Local moments; Orbital moments
Nuclear magnetic resonance (NMR) was used for the study of magnetic materials ever since this technique was introduced (see Refs. [1,2]). Recently, manganese compounds received growing interest for various reasons * be it local moment instability in intermetallic compounds, colossal magnetoresistance phenomena in manganites or ferro/imagnetism above room temperature for thin multi-component vapour deposited "lms. Here we want to point to two levels of sophistication in the application of Mn NMR in unravelling puzzles encountered in magnetism. A rather versatile application is the derivation of local 3d moments in the magnetically ordered state of intermetallic compounds with negligible 4s/p polarization. Under this condition, the general correlation between Mn NMR frequency (or hyper"ne "eld) and local magnetic (3d like) moment presented in Fig. 1 can be used [3}8]. It is a consequence of the predominating core polarization contribution to the hyper"ne interaction. It was supported by a detailed NMR analysis of the layered manganese compounds Gd Y Mn Ge [3,9,10] re\V V cently. Just the center of gravity of the respective NMR
* Corresponding author. Tel.: 00-49-721608-3455; fax: 00-49721608-6103. E-mail address: [email protected] (E. Dormann).
lines has to be used. Temperature dependence of the spontaneous local moment can be derived as well [3]. The correlation can also be applied in order + + to disentangle moment distributions. Accepting very long signal accumulation times, this can be used even for thin magnetic "lms. As recently ferromagnetism above room temperature was reported for Mn/C/Si triple layers prepared by sequential deposition at 3603C [11], whereas, only average moments of about 1 per Mn site were found by integral methods, an NMR analysis was required. In order to save space we refer to Ref. [12] and report only that two NMR line groups observed in zero"eld broad band NMR spectrum of Mn Si C "lms at 4.2 K point to distinct moments of about 3.0 and 1.9 necessarily arranged ferrimagnetically (6:4 ratio) in order to agree with the observed average moment. Thus, by the combination of integral magnetization measurements and NMR spectroscopy even local moment distributions are accessible. If the structural site has lower symmetry than axial (as realized for the manganese sites in the KagomeH net of RMn Ge ), Mn hyper"ne interaction can be much richer in information content than considered so far: The anisotropy of the magnetic hyper"ne interaction H "H #H (3 cos !1)!H sin cos
?L ?L
0304-8853/01/$ - see front matter 2001 Elsevier Science B.V. All rights reserved. PII: S 0 3 0 4 - 8 8 5 3 ( 0 0 ) 0 0 7 3 8 - 1
(1)
M.T. Kelemen et al. / Journal of Magnetism and Magnetic Materials 226}230 (2001) 1188}1189
1189
Table 1 Spin and orbital moments derived for GdMn Ge (MHz) + H H H
Fig. 1. Correlation of Mn NMR frequency (center of gravity) with Mn 3d-moment in compounds with negligible Mn 4s/p polarization.
223.4 !17.3 #26.7
H (kOe) 212.7 !16.5 #25.4
( ) 2.07 !0.034 #0.045
the orbital moments given in the last two lines of Table 1 are estimated (r\7 "2.868;10 cm\ [13]). Thus, anisotropy of the manganese hyper"ne interaction is substantial (about 20% for H ) in the layered struc ture of RMn Ge . The interpretation of this anisotropy by an orbital polarization of about 3}4;10\ is in agreement with the result of band structure calculations [3]. We thank K.H.J. Buschow and M. Gajdzik for the samples and the Deutsche Forschungsgemeinschaft for "nancial support.
References
Fig. 2. Simulated and measured Mn NMR spectra for GdMn Ge powder samples for high- and low-RF excitation power.
and of the electric quadrupole interaction (< ,) can be derived from the NMR spectra. To this aim, however, the magnetic structure of domains and walls and the peculiarities of the NMR enhancement mechanism in magnetically ordered materials have to be considered in detail [1}3,9,10]. The dependence of the NMR spectra on excitation conditions - as shown in Fig. 2 for example [3] * and the distribution of relaxation times have to be studied. Along these lines, the parameters " V 218.4 MHz, "201.4 MHz, "241.4 MHz, "5 MHz W X / and "0.6 were derived for Mn in GdMn Ge at 4.2 K. In addition to the known isotropic part, the anisotropy of the hyper"ne interaction (Table 1) is obtained. Assuming orbital polarization as its main origin, with H "!2 r\l , ,
(2)
[1] E. Dormann, NMR in intermetallic compounds, In: K. A. Gscheidner, L. Eyring (Eds.), Handbook on the Physics and Chemistry of Rare Earths, Vol. 14, Elsevier Science, Amsterdam, 1991, p. 63 (Chapter 94). [2] Cz. Kapusta, P.C. Riedi, G.J. Tomka, Magnetism of permanent magnet materials and related compounds as studied by NMR, In: K.H.J. Buschow (Ed.), Handbook of Magnetic Materials, Vol. 11, Elsevier Science, Amsterdam, 1998, p. 407 (Chapter 3). [3] M.T. Kelemen, Magnetische Ordnung und Hyperfeinwechselwirkung in ternaK ren Seltenerd-Mangan-Germanium-Verbindungen, Ph.D. Thesis UniversitaK t Karlsruhe and Cuvillier Verlag, GoK ttingen, 1999 [4] K. Shimizu, S.K. Dhar, R. Vijayaraghavan, S.K. Malik, J. Phys. Soc. Jpn. 50 (1981) 1200. [5] H. Nagai, Y. Ikami, H. Yoshie, A. Tsujimura, J. Phys. Soc. Jpn. 50 (1981) 1873. [6] E.V. Sampathkumaran, L.C. Gupta, R. Vijayaraghavan, Le Dang Khoi, P. Veillet, J. Phys. F 12 (1982) 1039. [7] K. Shimizu, J. Phys. Soc. Jpn. 54 (1985) 1154. [8] K. Yoshimura, M. Shiga, Y. Nakamura, J. Phys. Soc. Jpn. 55 (1986) 3585. [9] M.T. Kelemen, P. RoK sch, E. Dormann, K.H.J. Buschow, J. Magn. Magn. Mater. 188 (1998) 195. [10] P. RoK sch, M.T. Kelemen, E. Dormann, G. Tomka, P.C. Riedi, J. Phys.: Condens. Matter 12 (2000) 1065. [11] T. Takeuchi, M. Igarashi, Y. Hirayama, M. Futamoto, J. Appl. Phys. 78 (1995) 2132. [12] M.T. Kelemen, M. Gajdzik, Ch. SuK rgers, H.v. LoK hneysen, E. Dormann, Phys. Lett. 269 (2000) 234. [13] G.T. Rado, H. Suhl, Vol.II Magnetism, Part A, Academic Press, New York, 1965.
Manganese hyper"ne interaction in intermetallic Mn compounds M.T. Kelemen, Ch. SuK rgers, E. Dormann* Physikalisches Institut, Universita( t Karlsruhe, D-76128 Karlsruhe, Germany
Abstract Local manganese moments at di!erent lattice sites in intermetallic Mn compounds can be derived by analysis of the Mn nuclear magnetic resonance (NMR) spectra. This was used for Gd Y Mn Ge pseudoternary compounds and V \V Mn Si C "lms. Careful NMR line shape analysis also yields anisotropic hyper"ne and quadrupole interaction pointing to weak but non-negligible orbital moments. 2001 Elsevier Science B.V. All rights reserved. Keywords: NMR; Manganese; Local moments; Orbital moments
Nuclear magnetic resonance (NMR) was used for the study of magnetic materials ever since this technique was introduced (see Refs. [1,2]). Recently, manganese compounds received growing interest for various reasons * be it local moment instability in intermetallic compounds, colossal magnetoresistance phenomena in manganites or ferro/imagnetism above room temperature for thin multi-component vapour deposited "lms. Here we want to point to two levels of sophistication in the application of Mn NMR in unravelling puzzles encountered in magnetism. A rather versatile application is the derivation of local 3d moments in the magnetically ordered state of intermetallic compounds with negligible 4s/p polarization. Under this condition, the general correlation between Mn NMR frequency (or hyper"ne "eld) and local magnetic (3d like) moment presented in Fig. 1 can be used [3}8]. It is a consequence of the predominating core polarization contribution to the hyper"ne interaction. It was supported by a detailed NMR analysis of the layered manganese compounds Gd Y Mn Ge [3,9,10] re\V V cently. Just the center of gravity of the respective NMR
* Corresponding author. Tel.: 00-49-721608-3455; fax: 00-49721608-6103. E-mail address: [email protected] (E. Dormann).
lines has to be used. Temperature dependence of the spontaneous local moment can be derived as well [3]. The correlation can also be applied in order + + to disentangle moment distributions. Accepting very long signal accumulation times, this can be used even for thin magnetic "lms. As recently ferromagnetism above room temperature was reported for Mn/C/Si triple layers prepared by sequential deposition at 3603C [11], whereas, only average moments of about 1 per Mn site were found by integral methods, an NMR analysis was required. In order to save space we refer to Ref. [12] and report only that two NMR line groups observed in zero"eld broad band NMR spectrum of Mn Si C "lms at 4.2 K point to distinct moments of about 3.0 and 1.9 necessarily arranged ferrimagnetically (6:4 ratio) in order to agree with the observed average moment. Thus, by the combination of integral magnetization measurements and NMR spectroscopy even local moment distributions are accessible. If the structural site has lower symmetry than axial (as realized for the manganese sites in the KagomeH net of RMn Ge ), Mn hyper"ne interaction can be much richer in information content than considered so far: The anisotropy of the magnetic hyper"ne interaction H "H #H (3 cos !1)!H sin cos
?L ?L
0304-8853/01/$ - see front matter 2001 Elsevier Science B.V. All rights reserved. PII: S 0 3 0 4 - 8 8 5 3 ( 0 0 ) 0 0 7 3 8 - 1
(1)
M.T. Kelemen et al. / Journal of Magnetism and Magnetic Materials 226}230 (2001) 1188}1189
1189
Table 1 Spin and orbital moments derived for GdMn Ge (MHz) + H H H
Fig. 1. Correlation of Mn NMR frequency (center of gravity) with Mn 3d-moment in compounds with negligible Mn 4s/p polarization.
223.4 !17.3 #26.7
H (kOe) 212.7 !16.5 #25.4
( ) 2.07 !0.034 #0.045
the orbital moments given in the last two lines of Table 1 are estimated (r\7 "2.868;10 cm\ [13]). Thus, anisotropy of the manganese hyper"ne interaction is substantial (about 20% for H ) in the layered struc ture of RMn Ge . The interpretation of this anisotropy by an orbital polarization of about 3}4;10\ is in agreement with the result of band structure calculations [3]. We thank K.H.J. Buschow and M. Gajdzik for the samples and the Deutsche Forschungsgemeinschaft for "nancial support.
References
Fig. 2. Simulated and measured Mn NMR spectra for GdMn Ge powder samples for high- and low-RF excitation power.
and of the electric quadrupole interaction (< ,) can be derived from the NMR spectra. To this aim, however, the magnetic structure of domains and walls and the peculiarities of the NMR enhancement mechanism in magnetically ordered materials have to be considered in detail [1}3,9,10]. The dependence of the NMR spectra on excitation conditions - as shown in Fig. 2 for example [3] * and the distribution of relaxation times have to be studied. Along these lines, the parameters " V 218.4 MHz, "201.4 MHz, "241.4 MHz, "5 MHz W X / and "0.6 were derived for Mn in GdMn Ge at 4.2 K. In addition to the known isotropic part, the anisotropy of the hyper"ne interaction (Table 1) is obtained. Assuming orbital polarization as its main origin, with H "!2 r\l , ,
(2)
[1] E. Dormann, NMR in intermetallic compounds, In: K. A. Gscheidner, L. Eyring (Eds.), Handbook on the Physics and Chemistry of Rare Earths, Vol. 14, Elsevier Science, Amsterdam, 1991, p. 63 (Chapter 94). [2] Cz. Kapusta, P.C. Riedi, G.J. Tomka, Magnetism of permanent magnet materials and related compounds as studied by NMR, In: K.H.J. Buschow (Ed.), Handbook of Magnetic Materials, Vol. 11, Elsevier Science, Amsterdam, 1998, p. 407 (Chapter 3). [3] M.T. Kelemen, Magnetische Ordnung und Hyperfeinwechselwirkung in ternaK ren Seltenerd-Mangan-Germanium-Verbindungen, Ph.D. Thesis UniversitaK t Karlsruhe and Cuvillier Verlag, GoK ttingen, 1999 [4] K. Shimizu, S.K. Dhar, R. Vijayaraghavan, S.K. Malik, J. Phys. Soc. Jpn. 50 (1981) 1200. [5] H. Nagai, Y. Ikami, H. Yoshie, A. Tsujimura, J. Phys. Soc. Jpn. 50 (1981) 1873. [6] E.V. Sampathkumaran, L.C. Gupta, R. Vijayaraghavan, Le Dang Khoi, P. Veillet, J. Phys. F 12 (1982) 1039. [7] K. Shimizu, J. Phys. Soc. Jpn. 54 (1985) 1154. [8] K. Yoshimura, M. Shiga, Y. Nakamura, J. Phys. Soc. Jpn. 55 (1986) 3585. [9] M.T. Kelemen, P. RoK sch, E. Dormann, K.H.J. Buschow, J. Magn. Magn. Mater. 188 (1998) 195. [10] P. RoK sch, M.T. Kelemen, E. Dormann, G. Tomka, P.C. Riedi, J. Phys.: Condens. Matter 12 (2000) 1065. [11] T. Takeuchi, M. Igarashi, Y. Hirayama, M. Futamoto, J. Appl. Phys. 78 (1995) 2132. [12] M.T. Kelemen, M. Gajdzik, Ch. SuK rgers, H.v. LoK hneysen, E. Dormann, Phys. Lett. 269 (2000) 234. [13] G.T. Rado, H. Suhl, Vol.II Magnetism, Part A, Academic Press, New York, 1965.