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Suppression of the ferromagnetic state by disorder in the anisotropic Kondo lattice system UAsSe
Journal of Magnetism and Magnetic Materials 140-144 (1995) 1433-1434
,4~ ~4 ,4~
ELSEVIER
journalof magnetism and magnetic malerlals
Suppression of the ferromagnetic state by disorder in the anisotropic Kondo lattice system UAsSe Z. Henkie *, R. Fabrowski, A. Wojakowski, A.J. Zaleski W. Trzebiatowski Institute of Low Temperature and Structure Research, Polish Academy of Sciences, 50-950 Wroctaw 2, P.O. Box 937, Poland Abstract We have examined the basal-plane resistivity and ac susceptibility between 4.2 and 300 K for selected UAsSe crystals which order ferromagnetically below Tc varying from 102 to 109 K. We show that the decrease in the arsenium to selenium content ratio lowers Tc and enhances the incoherent Kondo resistivity in the ferromagnetic state.
UAsSe is a highly anisotropic ferromagnet below Tc = 113 K with c-axis the easy-magnetization axis (tetragonal structure) and localized-moment behaviour [1,2]. However, the magneto-optical Kerr-effect shows the presence of an f band at the Fermi energy and hence p - f hybridization [3]. The electrical resistivity decreases with temperature except in a small range between about T c / 2 and Tc [4,5]. A negative slope d p / d T of the isostructural diamagnetic ThAsSe is due to an increase of carrier concentration [5]. A recent study [6] of the anisotropy of the resistivity and of the Hall effect excluded such a case in UAsSe. Therefore we have examined the ac susceptibility and the sample dependence of the resistivity to better characterize this system. The ac magnetic susceptibility, consisting of in-phase X'(°)) and out-of-phase X"(W) components, was measured in a Lake Shore susceptometer in a magnetic field of frequency 400.0 Hz and amplitude 10 Oe. The resistivity was measured by a conventional dc method. The arsenium to selenium content ratio, ASCR, was determined in an EDAX scanning electron microscope by using a super U T W detector and E D A X energy dispersive X-ray analysis (0.1 at% sensitivity). This procedure gives an ASCR of 1 + 0.007 for UAsSe showing Tc = 113 K. It is assumed as an arbitrary reference composition. Results of ac susceptibility measurements for a UAsSe single crystal are shown in Figs. 1 and 2. Their main features are: anisotropy - ()('/)(')7"= rc = 33, high reduction of x ' ( T ) below T ~ - x ' ( T ~ ) / x ' ( T J 2 ) ~ 103, and Curie-Weiss behaviour of x~(T) above Tc. The X" and X~' are the in-phase components measured in a field along
the c- or a-axes, respectively. From the susceptibility in the temperature range O c < T < 125 K ( O c = 108.3 K is the Curie-Weiss temperature for the c-axis) where accuracy was the highest, an effective moment /xeff = 3.48#B was determined. The Curie-Weiss behaviour in the range T = Oc-320 K, with the same effective moment for the a- and c-axes and different O e and 0 a values, has been observed in dc susceptibility measurements in a field of 1.2 T on the sample composed of a few single crystals with a c-axis alignment accuracy of 5 - 6 ° [2]. UAsSe powder dc susceptibility Xp is characterized by temperature dependent d ( 1 / X p ) / d T between Tc and 600 K and by ~'£eff 3-42/XB determined in the range 6 0 0 - 9 0 0 K [1]. We can reproduce the Xp(T) behaviour for the /Xeff = 3.48/XB, the same for both the a- and c-axes, 0,. = Tc = 118 K [1], a fitted value O a = - 4 0 2 K and assuming Xp = 0.206Xc + 0.794X,. =
0.2
I
xl03
I
UAs Se
1/X~
oo°°Oe_
8 c=108 3 K
jmon
o.o ~ 0
o
,
,
-
-
.
1oo
~
~ 200
e.=3-48#'~ -
~
c
3 oo
T[K]
* Corresponding author. Fax: + 48-71-441029.
Fig. 1. Temperature dependence of the in-plane magnetic susceptibility X~. measured along the c-axis ( t ) , its reciprocal 1 / X ~ above Tc ((3) and X" ×100 below Tc ([]).
0304-8853/95/$09.50 © 1995 Elsevier Science B.V. All rights reserved
SSDI 0 3 0 4 - 8 8 5 3 ( 9 4 ) 0 0 8 8 6 - 8
Z. Henkie et al. / Journal of Magnetism and Magnetic Materials 140-144 (1995) 1433-1434
1434 0.2
-- '
,
U AS Se
'
oo
~
d5 10~
o
o
-
~.10 3
oOO~
,
x
]Lo
100 "
7,4
........
105 T [K]
~", ~ ~-1.0I1!-21~
P @ ~ 2 O 0
-,~, q i~
115
are guides for the eye.
Therefore we consider our ac susceptibility data as being consistent with the dc susceptibility data. A m a x i m u m in the d p / d T vs. T function occurs at the same temperature as that in x'(T). We assume this temperature to be Tc. The basal-plane resistivity o f four selected U A s S e crystals is given in Fig. 3. The crystals are labeled with number n from 1 to 4 in such a way that a higher n corresponds to higher Tc and a lower value of normalized residual resistivity R = p(4.2 K)/p(Tc). Data on the resistivity anisotropy o f sample 1 (T c = 102.0 K) allowed for an explicit identification o f scattering m e c h a n i s m s [6] contributing to total resistivity Pt with c o m p o n e n t s Pr, PK, Pph and Ps (inset (a) in Fig. 3).
5
110
Fig. 4. Axsenium to selenium content ratio ( O ) and the normalized resistivity at 4.2 K (O) as a function of Tc. The solid lines
110
Fig. 2. The in-phase magnetic susceptibility X" (O), its temperature derivative ( ) and out-of-phase susceptibility X;' ( • ) for the c-axis. The in-phase susceptibility X~ (rq and . . . . . . ) and temperature derivative of resistivity (Q) for the a-axis.
\\
105 T:[K]
- 2
°°°°o
•
o o ~ ] .......... ~X: 100
12
/e
%
°
UAsSe ~ / / 7
25
~ 0
100
,
i
, ,' '70 200 300
I
The ps(T) function is due to the scattering o f carriers by the spin disorder o f an R K K Y system. This function has temperature dependence similar to that o f the basalplane resistivity in the isostructural c o m p o u n d UAs 2. The PK represents an incoherent Kondo scattering well described in terms o f a Kondo limit o f the single impurity Anderson model o f Arai [7] when a Kondo temperature TI{ = 40 K is assumed [6]. The phonon resistivity Pph is described by the generalized B l o c h - G r t i n e i s e n formula. Pr is the temperature-independent residual resistivity due to some paramagnetic impurities. Below T = 25 K pt(T) is dominated by pK(T) and we show this range for samples 1, 3 and 4 in the inset (b) of Fig. 3. W e observe that the resistivity can be described by the Fermi liquid theory (FLT) formula p ~ [1 - (T/TK) 2 [8] in a wider temperature range for samples with lower R. The broken line in Fig. 3b presents the FLT formula fitted to curve 4 (T K = 74 K). The A S C R and R data are ploted versus Tc in Fig. 4. The figure demonstrates our main conclusion: the decrease in the A s / S e content ratio lowers Tc and enhances the incoherent Kondo resistivity in the ferromagnetic state. Acknowledgement: Work supported by the Committee for Scientific Research, Grant no. KBN-2 P302 173 06. References
I
0
I
i00
I
I
200 V [K]
n~4
300
Fig. 3. The basal-plane resistivity (normalized to its peak value) for selected UAsSe crystals. Inset (a) shows the total resistivity Pt for sample n = 1 and all its components: PK - Kondo, Ps spin-disorder, Pph - phonon, and Pr - residual resistivity. Inset (b) presents the low-temperature behaviour of the resistivity, normalized to its minimum value, for n = 1, 3 and 4.
[1] A. Zygmunt and M. Duczmal, Phys. Stat. Sol. (a) 9 (1972) 659. [2] K.P. Bielov, A.S. Dmitrievski, A. Zygmunt, R.Z. Levitin and W. Trzebiatowski, Zh. Eksp. Teor. Fiz. 64 (1973) 582. [3] W. Reim, J. Magn. Magn. Mater. 58 (1986) 1. [4] A. Wojakowski, Z. Henkie and Z. Kletowski, Phys. Stat. Sol. 14 (1972) 517. [5] J. Schoenes, W. Bacsa and F. Hulliger, Solid State Commun. 68 (1988) 287. [6] Z. Henkie, R. Fabrowski and A. Wojakowski, Acta Phys. Polon. A 85 (1994) 249; J. Alloys Comp. in press. [7] T. Arai, J. Appl. Phys. 57 (1985) 3161. [8] P. Nozi~res, J. Low Temp. Phys. 17 (1974) 31.
,4~ ~4 ,4~
ELSEVIER
journalof magnetism and magnetic malerlals
Suppression of the ferromagnetic state by disorder in the anisotropic Kondo lattice system UAsSe Z. Henkie *, R. Fabrowski, A. Wojakowski, A.J. Zaleski W. Trzebiatowski Institute of Low Temperature and Structure Research, Polish Academy of Sciences, 50-950 Wroctaw 2, P.O. Box 937, Poland Abstract We have examined the basal-plane resistivity and ac susceptibility between 4.2 and 300 K for selected UAsSe crystals which order ferromagnetically below Tc varying from 102 to 109 K. We show that the decrease in the arsenium to selenium content ratio lowers Tc and enhances the incoherent Kondo resistivity in the ferromagnetic state.
UAsSe is a highly anisotropic ferromagnet below Tc = 113 K with c-axis the easy-magnetization axis (tetragonal structure) and localized-moment behaviour [1,2]. However, the magneto-optical Kerr-effect shows the presence of an f band at the Fermi energy and hence p - f hybridization [3]. The electrical resistivity decreases with temperature except in a small range between about T c / 2 and Tc [4,5]. A negative slope d p / d T of the isostructural diamagnetic ThAsSe is due to an increase of carrier concentration [5]. A recent study [6] of the anisotropy of the resistivity and of the Hall effect excluded such a case in UAsSe. Therefore we have examined the ac susceptibility and the sample dependence of the resistivity to better characterize this system. The ac magnetic susceptibility, consisting of in-phase X'(°)) and out-of-phase X"(W) components, was measured in a Lake Shore susceptometer in a magnetic field of frequency 400.0 Hz and amplitude 10 Oe. The resistivity was measured by a conventional dc method. The arsenium to selenium content ratio, ASCR, was determined in an EDAX scanning electron microscope by using a super U T W detector and E D A X energy dispersive X-ray analysis (0.1 at% sensitivity). This procedure gives an ASCR of 1 + 0.007 for UAsSe showing Tc = 113 K. It is assumed as an arbitrary reference composition. Results of ac susceptibility measurements for a UAsSe single crystal are shown in Figs. 1 and 2. Their main features are: anisotropy - ()('/)(')7"= rc = 33, high reduction of x ' ( T ) below T ~ - x ' ( T ~ ) / x ' ( T J 2 ) ~ 103, and Curie-Weiss behaviour of x~(T) above Tc. The X" and X~' are the in-phase components measured in a field along
the c- or a-axes, respectively. From the susceptibility in the temperature range O c < T < 125 K ( O c = 108.3 K is the Curie-Weiss temperature for the c-axis) where accuracy was the highest, an effective moment /xeff = 3.48#B was determined. The Curie-Weiss behaviour in the range T = Oc-320 K, with the same effective moment for the a- and c-axes and different O e and 0 a values, has been observed in dc susceptibility measurements in a field of 1.2 T on the sample composed of a few single crystals with a c-axis alignment accuracy of 5 - 6 ° [2]. UAsSe powder dc susceptibility Xp is characterized by temperature dependent d ( 1 / X p ) / d T between Tc and 600 K and by ~'£eff 3-42/XB determined in the range 6 0 0 - 9 0 0 K [1]. We can reproduce the Xp(T) behaviour for the /Xeff = 3.48/XB, the same for both the a- and c-axes, 0,. = Tc = 118 K [1], a fitted value O a = - 4 0 2 K and assuming Xp = 0.206Xc + 0.794X,. =
0.2
I
xl03
I
UAs Se
1/X~
oo°°Oe_
8 c=108 3 K
jmon
o.o ~ 0
o
,
,
-
-
.
1oo
~
~ 200
e.=3-48#'~ -
~
c
3 oo
T[K]
* Corresponding author. Fax: + 48-71-441029.
Fig. 1. Temperature dependence of the in-plane magnetic susceptibility X~. measured along the c-axis ( t ) , its reciprocal 1 / X ~ above Tc ((3) and X" ×100 below Tc ([]).
0304-8853/95/$09.50 © 1995 Elsevier Science B.V. All rights reserved
SSDI 0 3 0 4 - 8 8 5 3 ( 9 4 ) 0 0 8 8 6 - 8
Z. Henkie et al. / Journal of Magnetism and Magnetic Materials 140-144 (1995) 1433-1434
1434 0.2
-- '
,
U AS Se
'
oo
~
d5 10~
o
o
-
~.10 3
oOO~
,
x
]Lo
100 "
7,4
........
105 T [K]
~", ~ ~-1.0I1!-21~
P @ ~ 2 O 0
-,~, q i~
115
are guides for the eye.
Therefore we consider our ac susceptibility data as being consistent with the dc susceptibility data. A m a x i m u m in the d p / d T vs. T function occurs at the same temperature as that in x'(T). We assume this temperature to be Tc. The basal-plane resistivity o f four selected U A s S e crystals is given in Fig. 3. The crystals are labeled with number n from 1 to 4 in such a way that a higher n corresponds to higher Tc and a lower value of normalized residual resistivity R = p(4.2 K)/p(Tc). Data on the resistivity anisotropy o f sample 1 (T c = 102.0 K) allowed for an explicit identification o f scattering m e c h a n i s m s [6] contributing to total resistivity Pt with c o m p o n e n t s Pr, PK, Pph and Ps (inset (a) in Fig. 3).
5
110
Fig. 4. Axsenium to selenium content ratio ( O ) and the normalized resistivity at 4.2 K (O) as a function of Tc. The solid lines
110
Fig. 2. The in-phase magnetic susceptibility X" (O), its temperature derivative ( ) and out-of-phase susceptibility X;' ( • ) for the c-axis. The in-phase susceptibility X~ (rq and . . . . . . ) and temperature derivative of resistivity (Q) for the a-axis.
\\
105 T:[K]
- 2
°°°°o
•
o o ~ ] .......... ~X: 100
12
/e
%
°
UAsSe ~ / / 7
25
~ 0
100
,
i
, ,' '70 200 300
I
The ps(T) function is due to the scattering o f carriers by the spin disorder o f an R K K Y system. This function has temperature dependence similar to that o f the basalplane resistivity in the isostructural c o m p o u n d UAs 2. The PK represents an incoherent Kondo scattering well described in terms o f a Kondo limit o f the single impurity Anderson model o f Arai [7] when a Kondo temperature TI{ = 40 K is assumed [6]. The phonon resistivity Pph is described by the generalized B l o c h - G r t i n e i s e n formula. Pr is the temperature-independent residual resistivity due to some paramagnetic impurities. Below T = 25 K pt(T) is dominated by pK(T) and we show this range for samples 1, 3 and 4 in the inset (b) of Fig. 3. W e observe that the resistivity can be described by the Fermi liquid theory (FLT) formula p ~ [1 - (T/TK) 2 [8] in a wider temperature range for samples with lower R. The broken line in Fig. 3b presents the FLT formula fitted to curve 4 (T K = 74 K). The A S C R and R data are ploted versus Tc in Fig. 4. The figure demonstrates our main conclusion: the decrease in the A s / S e content ratio lowers Tc and enhances the incoherent Kondo resistivity in the ferromagnetic state. Acknowledgement: Work supported by the Committee for Scientific Research, Grant no. KBN-2 P302 173 06. References
I
0
I
i00
I
I
200 V [K]
n~4
300
Fig. 3. The basal-plane resistivity (normalized to its peak value) for selected UAsSe crystals. Inset (a) shows the total resistivity Pt for sample n = 1 and all its components: PK - Kondo, Ps spin-disorder, Pph - phonon, and Pr - residual resistivity. Inset (b) presents the low-temperature behaviour of the resistivity, normalized to its minimum value, for n = 1, 3 and 4.
[1] A. Zygmunt and M. Duczmal, Phys. Stat. Sol. (a) 9 (1972) 659. [2] K.P. Bielov, A.S. Dmitrievski, A. Zygmunt, R.Z. Levitin and W. Trzebiatowski, Zh. Eksp. Teor. Fiz. 64 (1973) 582. [3] W. Reim, J. Magn. Magn. Mater. 58 (1986) 1. [4] A. Wojakowski, Z. Henkie and Z. Kletowski, Phys. Stat. Sol. 14 (1972) 517. [5] J. Schoenes, W. Bacsa and F. Hulliger, Solid State Commun. 68 (1988) 287. [6] Z. Henkie, R. Fabrowski and A. Wojakowski, Acta Phys. Polon. A 85 (1994) 249; J. Alloys Comp. in press. [7] T. Arai, J. Appl. Phys. 57 (1985) 3161. [8] P. Nozi~res, J. Low Temp. Phys. 17 (1974) 31.