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Magnetic state in RAgAl (R = Dy, Ho, Er)
Journal of Alloys and Compounds 423 (2006) 43–46
Magnetic state in RAgAl (R = Dy, Ho, Er) Jan Heimann ∗ , Dawid Dunikowski A. Chełkowski Institute of Physics, University of Silesia, Uniwersytecka 4, 40 007 Katowice, Poland Available online 7 February 2006
Abstract The polycrystalline intermetallics DyAgAl, HoAgAl and ErAgAl were obtained from a levitated melt. X-ray powder diffraction confirmed singlephase CeCu2 -type structure (Imma). The X-ray photoelectron spectra were obtained with a Physical Electronics PHI 5700/660 XPS spectrometer using monochromatized Al K␣ radiation. The magnetic measurements (in static fields of 35–2100 Oe) were carried out in the temperature range 4.2–600 K by the Faraday method. Above 50 K magnetic susceptibility follows Curie–Weiss law with θ parameter 35, 16, and 8 K for DyAgAl, HoAgAl and ErAgAl, respectively. The effective magnetic moments per rare earths atom are slightly higher than their free ion values. At low temperatures thermomagnetic effects between ZFC and cooled in field of 2500 Oe (FC) runs exist. The dc susceptibility versus temperature for ZFC runs shows a peak at 37, 18 and 13 K for DyAgAl, HoAgAl and ErAgAl, respectively. The ac susceptibility shows a cusp at 44, 24 and 15 K for DyAgAl, HoAgAl and ErAgAl, respectively. The electrical resistivity has been investigated in the temperature range 4.2–300 K. In the liquid helium (4.2 K) the resistivity values are large (2.69 m for DyAgAl, 2.78 m for HoAgAl and 3.39 m for ErAgAl). The temperature dependence of the resistivity of ErAgAl shows local maximum at 12.5 K (3.4 m) followed by minimum at 31 K (3.38 m). The thermomagnetic effects, cusps in ac and peaks in dc susceptibility indicate the spin glass state. HoAgAl may be considered as a cluster glass material. Disorder in nonmagnetic atoms sublattice causes the short mean path of the conduction electrons. The RKKY interactions are reduced to the closest neighbors. Randomly distributed Al and Ag atoms differ enough to disturb the symmetry in neighborhood of rare earths. In connection with reducing the range of the RKKY interactions it leads to NMAD driven spin glass state. © 2005 Elsevier B.V. All rights reserved. PACS: 71.20.Eh; 71.20.Lp; 75.20.En; 75.50.Lk Keywords: RAgAl; CeAl2 ; Rare-earth intermetallics; Magnetic susceptibility; Electrical resistivity; Spin glass; Magnetic frustration
1. Introduction Rare-earth ternary intermetallics RTX (R = rare earth, T = transition metal, X = nonmagnetic element) crystallize in high number of structural arrangements, providing material for investigations relations between crystal structure and magnetic behavior [1]. Among them the magnetic properties of RAgAl are relatively poorly known. The RAgAl compounds crystallize in the orthorhombic CeCu2 type structure which Hulliger mentioned as the first [2]. At present detailed structural data almost all of them are available [3] and some results of the investigations on magnetic properties and electrical resistivity for RAgAl compounds with Gd [4] and La, Ce, Pr, Nd, Tb as well as Er [5]. To our knowledge in literature there is no information about HoAgAl and for DyAgAl are only regarding the structure [3].
∗
Corresponding author. Fax: +48 32 588 431. E-mail address: [email protected] (J. Heimann).
0925-8388/$ – see front matter © 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.jallcom.2005.12.055
In the described in literature RAgAl (R = Ce, Pr, Nd, Tb and Gd) intermetallics spin glass behavior was found [4,5]. In the recent years spin freezing has been very attractive from both the experimental and theoretical points of view [6–8]. Usually in a spin glass system magnetic atom disorder (MAD) occurs [9]. In the RAgAl compounds, contrary to the classical spin glass systems, the magnetic atoms occupy a regular sublattice. They undergo spin glass freezing as result of disorder in Ag–Al sublattice, called as nonmagnetic atom disorder (NMAD) [9,10]. In this paper we report and discuss our result obtained from electrical resistivity and dc as well as ac magnetic susceptibility measurements of ErAgAl, DyAgAl and new compound HoAgAl. 2. Experimental The intermetallics RAgAl (where R = Dy, Ho and Er) were synthesized by melting in argon in the levitated state the stoichiometric amounts of the constituent elements: rare earth 99.9%, Ag specpure from Johnsons-Matthey and Al 99.999%. The polycrystalline cylindrical samples (length about 15 mm; diam-
44
J. Heimann, D. Dunikowski / Journal of Alloys and Compounds 423 (2006) 43–46
Table 1 Room temperature lattice parameters, magnetic properties and the residual resistivity ratio of investigated RAgAl intermetallic compounds Compound
a (nm)
b (nm)
c (nm)
µeff (µB /f.u.)
R3+ free ion µeff (µB )
θ (K)
Tf (K)
Tmax ZFC (K)
RRR (–)
DyAgAl HoAgAl ErAgAl
0.456 0.454 0.453
0.712 0.703 0.701
0.786 0.782 0.784
10.69 10.79 9.92
10.63 10.58 9.59
37.0 16.4 8.1
43.8 23.7 15.3
34.7 18.2 12.5
1.04 1.17 1.07
eter of 2, 2.2, 1.7 mm, respectively, for DyAgAl, HoAgAl and ErAgAl) were obtained by Czochralski method from levitating melt [11]. X-ray analysis was carried out at room temperature by means of Siemens D5000 powder diffractometer, with Cu K␣ radiation. The powder patterns structure refinement was done using the FULLPROF program [12]. The X-ray photoelectron spectra were obtained with a Physical Electronics PHI 5700/660 XPS spectrometer using monochromatized Al K␣ radiation. Its hemispherical analyzer ensures resolution of about 0.3 eV of kinetic energy of photoelectrons. The binding energies scale was calibrated using the Fermi level of Ag, peaks 4f of Au, 3d of Ag and 2p of Cu. Just prior to measurement, the samples were cleaved under high-vacuum conditions (about 10−10 hPa) in order to obtain a fresh surface, free of contaminants. For all samples the following spectra were measured: (1) an overview in the binding energy range of −2 to 1400 eV, (2) the valence band region −2 to 18 eV and (3) the characteristic peaks (for Ho, Dy and Er: 4d; for Ag: 3d; for Al: 2p). The background was subtracted using Tougaard’s approximation. To compare qualitatively the intensities of the valence band spectra, it was useful to do some rough scaling. From the overviews, we took the proportion of the maximum intensity near the Fermi level (between 4 and 7 eV) to the intensity of silver 3d peak. As the silver content is the same for all compounds, it was reasonable to normalize the overviews by these peaks and valence band spectra by the mentioned proportion. The spectra of elements were normalized by the intensity of the characteristic peaks. For convenience, at all temperatures and independent on magnetic state and magnetic behavior, we note χ = M/H and call χ as susceptibility. The temperature dependence of the dc magnetic susceptibility was measured in the range 4.2–600 K using the Faraday method in stationary magnetic fields (35 Oe at low temperatures and 1000 Oe above 77 K). The susceptibility values were corrected for diamagnetism by applying Slater–Angus constants. Temperature runs of the magnetic susceptibility for a sample cooled in zero field (ZFC) and cooled in a field of 2100 Oe (FC) were performed in the range 4.2–50 K at the measuring field 35 Oe. The ac susceptibility was measured in the ac field of 2 Oe and frequency about 1 kHz in the temperature range 4.2–300 K. The electrical resistivity has been investigated in the temperature range 4.2–300 K by a conventional method with a dc current of 100 mA.
states and moving them away of the Fermi level in comparison to the elemental Ag (Fig. 1). We generally expect narrower band widths in the investigated compounds than in elements, as the distances between atoms in the compound lattice are larger. So the larger distances lower the overlap of the 4d orbitals between neighboring Ag atoms. The temperature dependence of inverse of magnetic susceptibility of the investigated compounds is shown in Fig. 2. The magnetic susceptibility of HoAgAl and ErAgAl obeys Curie–Weiss law at temperatures higher than 40 K but DyAgAl for higher than 90 K. The fitting parameters, i.e. effective paramagnetic magnetic moments and paramagnetic Curie temperatures θ are collected in Table 1. The effective moments are little higher than the values of equivalent rare earth 3+ free ions (Table 1). The excess is probably connected with polarization of 3d electrons of silver [13]. Positive θ values suggest that in the investigated compounds ferromagnetic interactions are predominant. At low temperatures thermomagnetic effects occur (Fig. 3). The dc susceptibility measured at 4.2 K in field of 35 Oe reveals
3. Results and discussion The diffraction patterns show no evidence of other phases than single CeCu2 phase. The structure refinement estimated the room temperature lattice parameters (Table 1). The lattice parameters of DyAgAl and ErAgAl are in good agreement with those found by Fornasini et al. [3] and the parameters ErAgAl agree also well with reported by Suresh et al. [5]. Based on XPS measurements of characteristic peaks of the elements (rare earths: 4d; Ag: 3d; Al: 2p) we estimated the chemical compositions of the investigated compounds. We found that investigated samples had composition very close to the stoichiometric one. The XPS valence band spectra of the RAgAl compounds as well as elemental aluminum, silver and dysprosium are shown in Fig. 1. In the valence band region 4f states of rare earth and silver 4d are dominant. Density of states of aluminum electrons is very small in this region. There is visible narrowing the Ag 4d
Fig. 1. Valence band spectra of the investigated RAgAl compound and elements (Al, Ag, Dy).
J. Heimann, D. Dunikowski / Journal of Alloys and Compounds 423 (2006) 43–46
45
Fig. 2. Temperature dependence of inverse dc magnetic susceptibility of RAgAl measured in the field of 1000 Oe. The lines represent Curie–Weiss law.
Fig. 4. Temperature dependence of ac magnetic susceptibility of RAgAl measured at frequency of 1000 Hz in the ac field of 2 Oe. For accessibility imaginary parts of χac are presented only fragmentary, i.e. in the regions of visible changes.
big differences of values after cooling the samples in magnetic field of 2100 Oe (FC) and cooled without any field (ZFC). The FC runs are monotonically with temperature. There is a maximum in the temperature dependence of ZFC dc susceptibility of each RAgAl sample. The values of temperature at which susceptibility of RAgAl reaches a maximum (Tmax ZFC) are collected in Table 1. For DyAgAl and ErAgAl the ZFC and FC susceptibility branches join at temperature of the maximum. For HoAgAl compound ZFC and FC bring together at temperature higher than temperature of the maximum (Fig. 3), so in contrary to DyAgAl and ErAgAl we may consider HoAgAl as cluster glass material [14]. Fig. 4 shows temperature variation of ac susceptibility. The peaks in real part ac susceptibility occur at temperatures Tf 44, 24 and 15 K for DyAgAl, HoAgAl and ErAgAl, respectively (Table 1). The Tf temperatures are about 7 K higher than the corresponding θ values. The temperature dependence of electrical resistivity is shown in Fig. 5. The resistivity values are generally large due Coulomb scattering on non-periodic differences of electrical potential between silver and aluminum ions in disordered nonmagnetic
atoms sublattice. At the liquid helium temperature (4.2 K) they are 2.69 m for DyAgAl, 2.78 m for HoAgAl and 3.39 m for ErAgAl. In the temperature dependence of resistivity of DyAgAl and HoAgAl (Fig. 5) it is hardly to find any changes which may refer to their magnetic properties. The temperature dependence of the resistivity of ErAgAl shows pronounced local maximum at 12.5 K (3.4 m) followed by minimum at 31 K (3.38 m). The temperature values of the maximum and the maximum ZFC susceptibility ErAgAl (Table 1) are equal. Suresh et al. [5] obtained electrical resistivity values of ErAgAl about 35% lower and no maximum but drop below 10 K. It is reasonable to assume that RKKY interaction is responsible for magnetic behavior of intermetallics of rare earth with nonmagnetic elements. The short free path of the conduction electrons seriously influences the RKKY interaction [4]. The large resistivity of the investigated compounds reduces range of RKKY interaction to the nearest neighbors. Consequently nonmagnetic atom disorder responsible for local asymmetry and large resistivity of the compounds leads into spin glass state.
Fig. 3. Temperature dependence of dc magnetic susceptibility of RAgAl measured in the field of 35 Oe after cooling in field of 2100 Oe (FC) and zero-field cooling (ZFC).
Fig. 5. Temperature dependence of electrical resistivity of RAgAl measured with the dc current of 100 mA.
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J. Heimann, D. Dunikowski / Journal of Alloys and Compounds 423 (2006) 43–46
References [1] A. Szytuła, D. Fus, B. Penc, A. Jezierski, J. Alloys Compd. 317/318 (2001) 340. [2] F. Hulliger, J. Alloys Compd. 200 (1993) 75. [3] M.L. Fornasini, A. Iandelli, F. Merlo, M. Pani, Intermetallics 8 (2000) 239. [4] J. Heimann, M. Kulpa, J. Alloys Compd. 296 (2000) L8. [5] K.G. Suresh, S.K. Dhar, A.K. Nigam, J. Magn. Magn. Mater. 288 (2005) 452. [6] P.W. Anderson, Phys. Today (1990) 9.
[7] [8] [9] [10] [11] [12] [13] [14]
A.P. Young, Pramana: J. Phys. 64 (2005) 1087. G. Schehr, Phys. Rev. B 71 (2005) 184204. K.A. Gschneidner Jr., V.K. Pecharsky, Physica B 223/224 (1996) 131. K.A. Gschneidner Jr., J. Tang, S.K. Dhar, A. Goldman, Physica B 163 (1990) 507. E. Talik, J. Szade, J. Heimann, A. Winiarska, A. Winiarski, A. Chełkowski, J. Less-Comm. Met. 138 (1988) 129. J. Rodriguez-Carvajal, Physica B 192 (1993) 55. J. Szade, J. Heimann, A. Chełkowski, J. Magn. Magn. Mater. 88 (1990) 93. D.X. Li, S. Nimori, Y. Shiokawa, Physica B 359–361 (2005) 1114.
Magnetic state in RAgAl (R = Dy, Ho, Er) Jan Heimann ∗ , Dawid Dunikowski A. Chełkowski Institute of Physics, University of Silesia, Uniwersytecka 4, 40 007 Katowice, Poland Available online 7 February 2006
Abstract The polycrystalline intermetallics DyAgAl, HoAgAl and ErAgAl were obtained from a levitated melt. X-ray powder diffraction confirmed singlephase CeCu2 -type structure (Imma). The X-ray photoelectron spectra were obtained with a Physical Electronics PHI 5700/660 XPS spectrometer using monochromatized Al K␣ radiation. The magnetic measurements (in static fields of 35–2100 Oe) were carried out in the temperature range 4.2–600 K by the Faraday method. Above 50 K magnetic susceptibility follows Curie–Weiss law with θ parameter 35, 16, and 8 K for DyAgAl, HoAgAl and ErAgAl, respectively. The effective magnetic moments per rare earths atom are slightly higher than their free ion values. At low temperatures thermomagnetic effects between ZFC and cooled in field of 2500 Oe (FC) runs exist. The dc susceptibility versus temperature for ZFC runs shows a peak at 37, 18 and 13 K for DyAgAl, HoAgAl and ErAgAl, respectively. The ac susceptibility shows a cusp at 44, 24 and 15 K for DyAgAl, HoAgAl and ErAgAl, respectively. The electrical resistivity has been investigated in the temperature range 4.2–300 K. In the liquid helium (4.2 K) the resistivity values are large (2.69 m for DyAgAl, 2.78 m for HoAgAl and 3.39 m for ErAgAl). The temperature dependence of the resistivity of ErAgAl shows local maximum at 12.5 K (3.4 m) followed by minimum at 31 K (3.38 m). The thermomagnetic effects, cusps in ac and peaks in dc susceptibility indicate the spin glass state. HoAgAl may be considered as a cluster glass material. Disorder in nonmagnetic atoms sublattice causes the short mean path of the conduction electrons. The RKKY interactions are reduced to the closest neighbors. Randomly distributed Al and Ag atoms differ enough to disturb the symmetry in neighborhood of rare earths. In connection with reducing the range of the RKKY interactions it leads to NMAD driven spin glass state. © 2005 Elsevier B.V. All rights reserved. PACS: 71.20.Eh; 71.20.Lp; 75.20.En; 75.50.Lk Keywords: RAgAl; CeAl2 ; Rare-earth intermetallics; Magnetic susceptibility; Electrical resistivity; Spin glass; Magnetic frustration
1. Introduction Rare-earth ternary intermetallics RTX (R = rare earth, T = transition metal, X = nonmagnetic element) crystallize in high number of structural arrangements, providing material for investigations relations between crystal structure and magnetic behavior [1]. Among them the magnetic properties of RAgAl are relatively poorly known. The RAgAl compounds crystallize in the orthorhombic CeCu2 type structure which Hulliger mentioned as the first [2]. At present detailed structural data almost all of them are available [3] and some results of the investigations on magnetic properties and electrical resistivity for RAgAl compounds with Gd [4] and La, Ce, Pr, Nd, Tb as well as Er [5]. To our knowledge in literature there is no information about HoAgAl and for DyAgAl are only regarding the structure [3].
∗
Corresponding author. Fax: +48 32 588 431. E-mail address: [email protected] (J. Heimann).
0925-8388/$ – see front matter © 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.jallcom.2005.12.055
In the described in literature RAgAl (R = Ce, Pr, Nd, Tb and Gd) intermetallics spin glass behavior was found [4,5]. In the recent years spin freezing has been very attractive from both the experimental and theoretical points of view [6–8]. Usually in a spin glass system magnetic atom disorder (MAD) occurs [9]. In the RAgAl compounds, contrary to the classical spin glass systems, the magnetic atoms occupy a regular sublattice. They undergo spin glass freezing as result of disorder in Ag–Al sublattice, called as nonmagnetic atom disorder (NMAD) [9,10]. In this paper we report and discuss our result obtained from electrical resistivity and dc as well as ac magnetic susceptibility measurements of ErAgAl, DyAgAl and new compound HoAgAl. 2. Experimental The intermetallics RAgAl (where R = Dy, Ho and Er) were synthesized by melting in argon in the levitated state the stoichiometric amounts of the constituent elements: rare earth 99.9%, Ag specpure from Johnsons-Matthey and Al 99.999%. The polycrystalline cylindrical samples (length about 15 mm; diam-
44
J. Heimann, D. Dunikowski / Journal of Alloys and Compounds 423 (2006) 43–46
Table 1 Room temperature lattice parameters, magnetic properties and the residual resistivity ratio of investigated RAgAl intermetallic compounds Compound
a (nm)
b (nm)
c (nm)
µeff (µB /f.u.)
R3+ free ion µeff (µB )
θ (K)
Tf (K)
Tmax ZFC (K)
RRR (–)
DyAgAl HoAgAl ErAgAl
0.456 0.454 0.453
0.712 0.703 0.701
0.786 0.782 0.784
10.69 10.79 9.92
10.63 10.58 9.59
37.0 16.4 8.1
43.8 23.7 15.3
34.7 18.2 12.5
1.04 1.17 1.07
eter of 2, 2.2, 1.7 mm, respectively, for DyAgAl, HoAgAl and ErAgAl) were obtained by Czochralski method from levitating melt [11]. X-ray analysis was carried out at room temperature by means of Siemens D5000 powder diffractometer, with Cu K␣ radiation. The powder patterns structure refinement was done using the FULLPROF program [12]. The X-ray photoelectron spectra were obtained with a Physical Electronics PHI 5700/660 XPS spectrometer using monochromatized Al K␣ radiation. Its hemispherical analyzer ensures resolution of about 0.3 eV of kinetic energy of photoelectrons. The binding energies scale was calibrated using the Fermi level of Ag, peaks 4f of Au, 3d of Ag and 2p of Cu. Just prior to measurement, the samples were cleaved under high-vacuum conditions (about 10−10 hPa) in order to obtain a fresh surface, free of contaminants. For all samples the following spectra were measured: (1) an overview in the binding energy range of −2 to 1400 eV, (2) the valence band region −2 to 18 eV and (3) the characteristic peaks (for Ho, Dy and Er: 4d; for Ag: 3d; for Al: 2p). The background was subtracted using Tougaard’s approximation. To compare qualitatively the intensities of the valence band spectra, it was useful to do some rough scaling. From the overviews, we took the proportion of the maximum intensity near the Fermi level (between 4 and 7 eV) to the intensity of silver 3d peak. As the silver content is the same for all compounds, it was reasonable to normalize the overviews by these peaks and valence band spectra by the mentioned proportion. The spectra of elements were normalized by the intensity of the characteristic peaks. For convenience, at all temperatures and independent on magnetic state and magnetic behavior, we note χ = M/H and call χ as susceptibility. The temperature dependence of the dc magnetic susceptibility was measured in the range 4.2–600 K using the Faraday method in stationary magnetic fields (35 Oe at low temperatures and 1000 Oe above 77 K). The susceptibility values were corrected for diamagnetism by applying Slater–Angus constants. Temperature runs of the magnetic susceptibility for a sample cooled in zero field (ZFC) and cooled in a field of 2100 Oe (FC) were performed in the range 4.2–50 K at the measuring field 35 Oe. The ac susceptibility was measured in the ac field of 2 Oe and frequency about 1 kHz in the temperature range 4.2–300 K. The electrical resistivity has been investigated in the temperature range 4.2–300 K by a conventional method with a dc current of 100 mA.
states and moving them away of the Fermi level in comparison to the elemental Ag (Fig. 1). We generally expect narrower band widths in the investigated compounds than in elements, as the distances between atoms in the compound lattice are larger. So the larger distances lower the overlap of the 4d orbitals between neighboring Ag atoms. The temperature dependence of inverse of magnetic susceptibility of the investigated compounds is shown in Fig. 2. The magnetic susceptibility of HoAgAl and ErAgAl obeys Curie–Weiss law at temperatures higher than 40 K but DyAgAl for higher than 90 K. The fitting parameters, i.e. effective paramagnetic magnetic moments and paramagnetic Curie temperatures θ are collected in Table 1. The effective moments are little higher than the values of equivalent rare earth 3+ free ions (Table 1). The excess is probably connected with polarization of 3d electrons of silver [13]. Positive θ values suggest that in the investigated compounds ferromagnetic interactions are predominant. At low temperatures thermomagnetic effects occur (Fig. 3). The dc susceptibility measured at 4.2 K in field of 35 Oe reveals
3. Results and discussion The diffraction patterns show no evidence of other phases than single CeCu2 phase. The structure refinement estimated the room temperature lattice parameters (Table 1). The lattice parameters of DyAgAl and ErAgAl are in good agreement with those found by Fornasini et al. [3] and the parameters ErAgAl agree also well with reported by Suresh et al. [5]. Based on XPS measurements of characteristic peaks of the elements (rare earths: 4d; Ag: 3d; Al: 2p) we estimated the chemical compositions of the investigated compounds. We found that investigated samples had composition very close to the stoichiometric one. The XPS valence band spectra of the RAgAl compounds as well as elemental aluminum, silver and dysprosium are shown in Fig. 1. In the valence band region 4f states of rare earth and silver 4d are dominant. Density of states of aluminum electrons is very small in this region. There is visible narrowing the Ag 4d
Fig. 1. Valence band spectra of the investigated RAgAl compound and elements (Al, Ag, Dy).
J. Heimann, D. Dunikowski / Journal of Alloys and Compounds 423 (2006) 43–46
45
Fig. 2. Temperature dependence of inverse dc magnetic susceptibility of RAgAl measured in the field of 1000 Oe. The lines represent Curie–Weiss law.
Fig. 4. Temperature dependence of ac magnetic susceptibility of RAgAl measured at frequency of 1000 Hz in the ac field of 2 Oe. For accessibility imaginary parts of χac are presented only fragmentary, i.e. in the regions of visible changes.
big differences of values after cooling the samples in magnetic field of 2100 Oe (FC) and cooled without any field (ZFC). The FC runs are monotonically with temperature. There is a maximum in the temperature dependence of ZFC dc susceptibility of each RAgAl sample. The values of temperature at which susceptibility of RAgAl reaches a maximum (Tmax ZFC) are collected in Table 1. For DyAgAl and ErAgAl the ZFC and FC susceptibility branches join at temperature of the maximum. For HoAgAl compound ZFC and FC bring together at temperature higher than temperature of the maximum (Fig. 3), so in contrary to DyAgAl and ErAgAl we may consider HoAgAl as cluster glass material [14]. Fig. 4 shows temperature variation of ac susceptibility. The peaks in real part ac susceptibility occur at temperatures Tf 44, 24 and 15 K for DyAgAl, HoAgAl and ErAgAl, respectively (Table 1). The Tf temperatures are about 7 K higher than the corresponding θ values. The temperature dependence of electrical resistivity is shown in Fig. 5. The resistivity values are generally large due Coulomb scattering on non-periodic differences of electrical potential between silver and aluminum ions in disordered nonmagnetic
atoms sublattice. At the liquid helium temperature (4.2 K) they are 2.69 m for DyAgAl, 2.78 m for HoAgAl and 3.39 m for ErAgAl. In the temperature dependence of resistivity of DyAgAl and HoAgAl (Fig. 5) it is hardly to find any changes which may refer to their magnetic properties. The temperature dependence of the resistivity of ErAgAl shows pronounced local maximum at 12.5 K (3.4 m) followed by minimum at 31 K (3.38 m). The temperature values of the maximum and the maximum ZFC susceptibility ErAgAl (Table 1) are equal. Suresh et al. [5] obtained electrical resistivity values of ErAgAl about 35% lower and no maximum but drop below 10 K. It is reasonable to assume that RKKY interaction is responsible for magnetic behavior of intermetallics of rare earth with nonmagnetic elements. The short free path of the conduction electrons seriously influences the RKKY interaction [4]. The large resistivity of the investigated compounds reduces range of RKKY interaction to the nearest neighbors. Consequently nonmagnetic atom disorder responsible for local asymmetry and large resistivity of the compounds leads into spin glass state.
Fig. 3. Temperature dependence of dc magnetic susceptibility of RAgAl measured in the field of 35 Oe after cooling in field of 2100 Oe (FC) and zero-field cooling (ZFC).
Fig. 5. Temperature dependence of electrical resistivity of RAgAl measured with the dc current of 100 mA.
46
J. Heimann, D. Dunikowski / Journal of Alloys and Compounds 423 (2006) 43–46
References [1] A. Szytuła, D. Fus, B. Penc, A. Jezierski, J. Alloys Compd. 317/318 (2001) 340. [2] F. Hulliger, J. Alloys Compd. 200 (1993) 75. [3] M.L. Fornasini, A. Iandelli, F. Merlo, M. Pani, Intermetallics 8 (2000) 239. [4] J. Heimann, M. Kulpa, J. Alloys Compd. 296 (2000) L8. [5] K.G. Suresh, S.K. Dhar, A.K. Nigam, J. Magn. Magn. Mater. 288 (2005) 452. [6] P.W. Anderson, Phys. Today (1990) 9.
[7] [8] [9] [10] [11] [12] [13] [14]
A.P. Young, Pramana: J. Phys. 64 (2005) 1087. G. Schehr, Phys. Rev. B 71 (2005) 184204. K.A. Gschneidner Jr., V.K. Pecharsky, Physica B 223/224 (1996) 131. K.A. Gschneidner Jr., J. Tang, S.K. Dhar, A. Goldman, Physica B 163 (1990) 507. E. Talik, J. Szade, J. Heimann, A. Winiarska, A. Winiarski, A. Chełkowski, J. Less-Comm. Met. 138 (1988) 129. J. Rodriguez-Carvajal, Physica B 192 (1993) 55. J. Szade, J. Heimann, A. Chełkowski, J. Magn. Magn. Mater. 88 (1990) 93. D.X. Li, S. Nimori, Y. Shiokawa, Physica B 359–361 (2005) 1114.