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Magnetoelastic properties of a 5f-band metamagnet UCoAl
Physica B 284}288 (2000) 1299}1300
Magnetoelastic properties of a 5f-band metamagnet UCoAl F. Honda , T. Kagayama , G. Oomi *, L. Havela, V. SechovskyH , A.V. Andreev Department of Mechanical Engineering and Materials Science, Kumamoto University, Kumamoto 860-8555, Japan Department of Electronic Structures, Charles University, 121 16 Prague 2, Czech Republic Institute of Physics, Academy of Sciences of the Czech Republic, 182 21 Prague 8, Czech Republic
Abstract Thermal expansion and magnetostriction of UCoAl have been measured in order to clarify the magnetoelastic properties of 5f-band metamagnet UCoAl. The critical magnetic "eld increases with pressure at a rate of 0.28 T/GPa. It is also found that the metamagnetic transition is strongly a!ected by the lattice compression in basal plane. 2000 Published by Elsevier Science B.V. All rights reserved. Keywords: Band metamagnet; High pressure; Magnetostriction; UCoAl
UCoAl is one of the materials displaying the e!ect of band metamagnetism, which is characterized by nonmagnetic (NM) ground state and a "eld-induced ferromagnetic state. An appreciable 5f}3d hybridization in UCoAl does not allow formation of magnetic (M) ordering, but it is close to the M}NM borderline. In contrast to a few archetypal band metamagnets like YCo [1], UCoAl metamagnetism is based on the 5f magnetic moments and exhibits a strong anisotropy [2]. Magnetostriction and thermal expansion study are performed on the same single crystal as in Refs. [3,4]. We have used a sample cut into a cubic shape, oriented with the c-axis of the hexagonal structure (easy-magnetization axis) along the direction of the external magnetic "eld. Two strain gauges were mounted on opposite faces of the cube to detect strains along the c-axis and perpendicular to it (a-direction). The prepared single crystal is characterized by a very sharp "rst-order transition at magnetic "eld l H"0.65 T. Fig. 1 shows the temper ature dependence of the relative length changes along both axes. One should note the large anisotropy. At room temperature we can deduce thermal expansion coe$cients a "17;10\ K\ and a "6;10\ K\. ? Another remarkable feature is the minimum of *¸/¸ for
* Corresponding author. E-mail address: [email protected] (G. Oomi)
the c-direction. This temperature can be associated for example with a characteristic temperature of spin #uctuations observed in the temperature dependence of electrical resistivity [3]. The anisotropy in a has been observed in most of the UTX compounds studied until now, and is probably related to the anisotropy of the 5f bonding [5]. When studying the forced magnetostriction at ¹"2.0 K (Fig. 2), we found out that the metamagnetic transition, which is completed in a "eld of 0.9 T, leads to a step-like lattice expansion in the basal plane (a-axis), *¸/¸ "1.7;10\, whereas the lattice along the c-axis ? contracts, *¸/¸ "!1.5;10\. The higher multipli city of the a-axis leads to a total positive e!ect in the volume *
0921-4526/00/$ - see front matter 2000 Published by Elsevier Science B.V. All rights reserved. PII: S 0 9 2 1 - 4 5 2 6 ( 9 9 ) 0 2 5 7 7 - 6
1300
F. Honda et al. / Physica B 284}288 (2000) 1299}1300
Fig. 1. Relative variations of the lattice parameters a and c, and related variations of the relative volume.
Fig. 3. Critical metamagnetic "eld H (left scale) and the relative expansion at the transition along the a-axis (right scale) depending on the relative a-axis compression at ¹"273 K. The full line represents the quadratic "t mentioned in the text.
Fellowships of the Japan Society for the Promotion of Science for Young Scientists.
Fig. 2. Forced magnetostriction measured for the a- and c-axis of UCoAl at ¹"2.0 K.
*
Acknowledgements This work was supported by the Grant Agency of the Czech Republic (Grant No. 202/99/0184) and Research
References [1] T. Goto, H. Aruga Katori, T. Sakakibara, H. Mitamura, K. Fukamichi, K. Murata, J. Appl. Phys. 76 (1994) 6682. [2] A.V. Andreev, M.I. Bartashevich, T. Goto, K. Kamishima, L. Havela, V. Sechovsky, Phys. Rev. B 55 (1997) 5847. [3] L. Havela et al., Physica B, at the same conference. [4] N.V. Mushnikov, T. Goto, K. Kamishima, H. Yamada, A.V. Andreev, Y. Shiokawa, A. Iwao, V. Sechovsky, Phys. Rev. B 59 (1999) 6877. [5] V. Sechovsky, L. Havela, in: K.H.J. Buschow (Ed.), Handbook of Magnetic Materials, Vol. 11, North-Holland, Amsterdam, 1998, pp. 1}289. [6] A.V. Andreev, R.Z. Levitin, Yu.F. Popov, R.Yu. Yumaguzhin, Soviet Phys. Solid State 27 (1985) 1145.
Magnetoelastic properties of a 5f-band metamagnet UCoAl F. Honda , T. Kagayama , G. Oomi *, L. Havela, V. SechovskyH , A.V. Andreev Department of Mechanical Engineering and Materials Science, Kumamoto University, Kumamoto 860-8555, Japan Department of Electronic Structures, Charles University, 121 16 Prague 2, Czech Republic Institute of Physics, Academy of Sciences of the Czech Republic, 182 21 Prague 8, Czech Republic
Abstract Thermal expansion and magnetostriction of UCoAl have been measured in order to clarify the magnetoelastic properties of 5f-band metamagnet UCoAl. The critical magnetic "eld increases with pressure at a rate of 0.28 T/GPa. It is also found that the metamagnetic transition is strongly a!ected by the lattice compression in basal plane. 2000 Published by Elsevier Science B.V. All rights reserved. Keywords: Band metamagnet; High pressure; Magnetostriction; UCoAl
UCoAl is one of the materials displaying the e!ect of band metamagnetism, which is characterized by nonmagnetic (NM) ground state and a "eld-induced ferromagnetic state. An appreciable 5f}3d hybridization in UCoAl does not allow formation of magnetic (M) ordering, but it is close to the M}NM borderline. In contrast to a few archetypal band metamagnets like YCo [1], UCoAl metamagnetism is based on the 5f magnetic moments and exhibits a strong anisotropy [2]. Magnetostriction and thermal expansion study are performed on the same single crystal as in Refs. [3,4]. We have used a sample cut into a cubic shape, oriented with the c-axis of the hexagonal structure (easy-magnetization axis) along the direction of the external magnetic "eld. Two strain gauges were mounted on opposite faces of the cube to detect strains along the c-axis and perpendicular to it (a-direction). The prepared single crystal is characterized by a very sharp "rst-order transition at magnetic "eld l H"0.65 T. Fig. 1 shows the temper ature dependence of the relative length changes along both axes. One should note the large anisotropy. At room temperature we can deduce thermal expansion coe$cients a "17;10\ K\ and a "6;10\ K\. ? Another remarkable feature is the minimum of *¸/¸ for
* Corresponding author. E-mail address: [email protected] (G. Oomi)
the c-direction. This temperature can be associated for example with a characteristic temperature of spin #uctuations observed in the temperature dependence of electrical resistivity [3]. The anisotropy in a has been observed in most of the UTX compounds studied until now, and is probably related to the anisotropy of the 5f bonding [5]. When studying the forced magnetostriction at ¹"2.0 K (Fig. 2), we found out that the metamagnetic transition, which is completed in a "eld of 0.9 T, leads to a step-like lattice expansion in the basal plane (a-axis), *¸/¸ "1.7;10\, whereas the lattice along the c-axis ? contracts, *¸/¸ "!1.5;10\. The higher multipli city of the a-axis leads to a total positive e!ect in the volume *
0921-4526/00/$ - see front matter 2000 Published by Elsevier Science B.V. All rights reserved. PII: S 0 9 2 1 - 4 5 2 6 ( 9 9 ) 0 2 5 7 7 - 6
1300
F. Honda et al. / Physica B 284}288 (2000) 1299}1300
Fig. 1. Relative variations of the lattice parameters a and c, and related variations of the relative volume.
Fig. 3. Critical metamagnetic "eld H (left scale) and the relative expansion at the transition along the a-axis (right scale) depending on the relative a-axis compression at ¹"273 K. The full line represents the quadratic "t mentioned in the text.
Fellowships of the Japan Society for the Promotion of Science for Young Scientists.
Fig. 2. Forced magnetostriction measured for the a- and c-axis of UCoAl at ¹"2.0 K.
*
Acknowledgements This work was supported by the Grant Agency of the Czech Republic (Grant No. 202/99/0184) and Research
References [1] T. Goto, H. Aruga Katori, T. Sakakibara, H. Mitamura, K. Fukamichi, K. Murata, J. Appl. Phys. 76 (1994) 6682. [2] A.V. Andreev, M.I. Bartashevich, T. Goto, K. Kamishima, L. Havela, V. Sechovsky, Phys. Rev. B 55 (1997) 5847. [3] L. Havela et al., Physica B, at the same conference. [4] N.V. Mushnikov, T. Goto, K. Kamishima, H. Yamada, A.V. Andreev, Y. Shiokawa, A. Iwao, V. Sechovsky, Phys. Rev. B 59 (1999) 6877. [5] V. Sechovsky, L. Havela, in: K.H.J. Buschow (Ed.), Handbook of Magnetic Materials, Vol. 11, North-Holland, Amsterdam, 1998, pp. 1}289. [6] A.V. Andreev, R.Z. Levitin, Yu.F. Popov, R.Yu. Yumaguzhin, Soviet Phys. Solid State 27 (1985) 1145.