- Email: [email protected]
Hybridization and magnetism in U(Ru, Rh)X, X=Al, Ga
Physica B 177 (1992) North-Holland
PHY!ltCA 1
164-168
Hybridization
and magnetism
in U(Ru, Rh)X, X = Al, Ga
V. Sechovsky’, L. Havela”, F.R. de Boerb, P.A. Veenhuizen’, K. Sugiyama”, T. Kuroda’, E. Sugiura’, M. One’, M. DateC and A. Yamagishi’ “Department of Metal Physics, Charles University, Ke Karlovu 5, CS-12116 Prague 2, Czechoslovakia ‘Van der Waals-Zeeman Laboratory, University of Amsterdam, Valckenierstraat 65, 1018 XE Amsterdam, The Netherlands ‘Department of Physics, Osaka University, Toyonaka, Osaka 560, Japan
Results of magnetic studies of pseudoternary U(Ru, Rh)Al and U(Ru, 5f-4d hybridization with increasing Rh content is reflected in a gradual behaviour in URuX to ferromagnetism in URhX. The huge uniaxial anisotropic 5f-ligand hybridization.
1. Introduction URuAl, URuGa, URhAl and URhGa crystallize in the hexagonal ZrNiAl-type structure [l]. URhAl and URhGa are ferromagnetic below T, = 27 and 41 K, respectively [2]. URuAl and URuGa remain paramagnetic down to 20 mK [3]. Below 100 K, their magnetic susceptibilities deviate significantly from the high temperature Curie-Weiss behaviour. The JY(T) curve of URuAl exhibits a broad maximum at 50 K whereas a plateau and a low temperature upturn are found for URuGa [3]. These anomalies are reminiscent of the behaviour of the spin fluctuation materials UPt, and UAl,, respectively. Studies of URuAl and URhAl single crystals proved strong uniaxial magnetic anisotropy [4] which is common for UTX (T = transition metal, X = p-metal) compounds with the same structure [5]. In order to follow the transition from the non-magnetic state in URuX to ferromagnetism in URhX, we studied the magnetic behaviour of a number of pseudoternary compounds from the series URu,_,Rh,Al and URu,-.Rh,Ga. Results obtained on URu,_,Rh,Al [4] demonstrated a gradual reduction of the characteristic spin fluctuation energy with increasing Rh content, 0921-4526/92/$05.00
0
1992 - Elsevier
Science
Publishers
Rh)Ga systems are presented. Reduction of the transition from paramagnetic (spin fluctuation) magnetic anisotropy can be attributed to the
leading to ferromagnetism for x 2 0.23. Here, we compare this behaviour with results obtained on the analogous system U(Ru, Rh)Ga.
2. Experimental Polycrystalline samples of URu,_,Rh,Ga compounds have been prepared by arc melting under an argon atmosphere. All samples were single phase with the ZrNiAl-type structure. The lattice constants a and c vary almost linearly with x between those of URuGa, a = 707.6 pm, c =381.8pm, and URhGa, a =700.6pm, c= 394.5 pm. The magnetic susceptibility was measured on bulk samples in a SHE squid magnetometer in the temperature range 5-300 K. Magnetization curves at 4.2 K in fields B d 35 T were measured in the High Field Installation at the University of Amsterdam. Measurements of URuAl up to 60 T were performed in the High Field Installation at Osaka University. The magnetization was measured on two kinds of fine-powder samples: (a) loose powder grains which are oriented by the maximum magnetic field (free powder). (b) powder consisting of randomly oriented grains fixed by frozen alcohol (fixed powder).
B.V. All rights
reserved
V. Sechovsky et al. I Hybridization
and magnetism in U(Ru, Rh)X
165
On the free powder, we obtain the magnetization (M,,) in the easy magnetization direction, provided that the powder particles are single crystals and that they are fully oriented by the applied magnetic field. The fixed powder has the magnetization (Mrnd) of an ideal polycrystal. T200 ’
3. Results and discussion
t
The temperature dependence of the magnetic susceptibility x(T) of URuGa (fig. 1) at high temperatures (T > 100 K) can be described by a Curie-Weiss law including a temperature-independent contribution x0 = 1 x lo-’ m3/mol, x = CI(T-
0,) +x0 )
(1)
with 0, = -192 K. By gradual Rh substitution (fig. l), the Curie-Weiss behaviour is extended to lower temperatures and an upturn develops in the low temperature plateau of the x(T) curve. Moreover, the originally large negative Or, values are reduced very fast (fig. 2). Ferromagnetism occurs for x > 0.2 where the 0, values become 2 .
-250 ’ 0.0
0.2
0.4
0.6 X
Fig. 2. Concentration dependences of the paramagnetic Curie temperature 0, of URu,-,Rh,AI and URu,-,Rh,Ga. The lines are guides to the eye.
positive and both 0, and the ordering temperature T, (see fig. 3) increase with further increasing x. The magnetization curves of URuGa and URuAl at 4.2 K are compared in fig. 4. The high-field upturn in the M(B) curve of URuAl obtained in measurements up to 35 T has been reported previously [3,6]. The free powder measurement extended to 60 T reveals that aM/a B has a maximum at about 25 T and that the magnetization tends to saturate at higher fields. Linear extrapolation of M versus 1 lB to l/B = 0 yields an estimate of the saturated magnetic 50
. .
E
\
.
mE ?O ;I
I 1.0
0.8
URu,_,Rh,Ga
. 5
i
0
40 /*
30
r:
1.5
z
8
” t+ 20
0 0.0
0 0
50
150
100 TIKI
Fig. 1. Temperature dependence of the susceptibility of Uru,_,Rh,Ga for the concentrations x = 0 (O), 0.1 (0), 0.2 (A) and 0.3 (A). The lines represent Curie-Weiss fits.
0.2
0.4
0.6
0.8
1.0
X Fig.
3. Concentration dependences of 7-c (circles) and (triangles) of U(Ru,_,Rh,)AI (open symbols) and U(Ru,_,Rh,)Ga (full symbols). The lines are guides to the eye.
Mt
V. Sechovsky et al. I Hybridization and magnetism in U(Ru,
166
r
06
Rh)X
trapolating M versus B to B = 0 T) increases with increasing Rh content (fig. 3). Comparison of the free powder and the fixed powder magnetizations (figs. 5 and 6, respectively) reveals strong magnetic anisotropy in all URu,_,Rh,Ga compounds. In case of uniaxial anisotropy,
0.5
IO
30
20
40
50
60
B (I.1
Fig. 4. Magnetization curves of URuAl and URuGa at 4.2 K measured on field-oriented powder and fixed powder.
moment of 0.84&f.u. The free powder M(B) curve of URuGa also displays an upturn (but much less pronounced) above 20 T. Fields higher than 35 T are needed to study further details of this anomaly. The M(B) curves of all URu, _,Rh,Ga compounds measured on free powders (fig. 5) demonstrate a development of magnetism similar to that in URu,_,Rh,Al [6]. The slight upturn persists in URu,.,Rh,, 1Ga. The magnetization is enhanced with increasing x and, for x > 0.2, we observe ferromagnetic ordering. The spontaneous magnetization M’, (estimated by ex0.7
M,, = M; + Bxc ,
(2)
M rnd = M;l2 + Bxc/3 + 2B~~.~/3,
(3)
provided that the susceptibilities (x = dMld B) xc (along the c-axis) and xa,b (in the basal plane) are field independent. Then we can derive the anisotropic parameters xc, xa,b and Mi from powder data. In fig. 7, we can see that for ferromagnetic compounds M,,= 2M,,, in B = OT, which indicates uniaxial anisotropy. For paramagnets as URuGa, M',= 0 and the difference 3M,,, - M,, = ~Bx~,~. The M',results of U(Ru, Rh)Ga are displayed in fig. 3. While the X a7b values are almost concentration-independent across the series (2.8 x lo-’ m3/mol in URuGa, 2.1 x lop8 m3/mol in URhGa), the easy axis susceptibilities are much larger for paramagnetic compounds (5.1 X lo-’ m3/mol in URuAl) than in the ferromagnetic ones (2.4 x lo-* m3/mol in URhGa). The development of magnetism in UTX compounds, as in many other actinide intermetallics 1.5
X= 1.0
1 X=
0.6
0
IO
20
30
40
13CT)
Fig. 5. Magnetization curves of URu,_,Rh,Ga at 4.2 K, for different compositions, measured on field-oriented powders. The lines are guides to the eye.
B (‘0
Fig. 6. Magnetization curves of polycrystalline URu,_,Rh,Ga (fixed powder) at 4.2 K for different compositions. The lines are guides to the eye.
V. Sechovsky et al. I Hybridization
URhGa
o,ov 0
IO
’ 20
30
40
B CT)
Fig. 7. Comparison of magnetization curves of URuGa, URu,, ,Rh, ,Ga and URhGa at 4.2K measured on fieldoriented powder and fixed powder. The lines are guides to the eye.
[5,7], can be conceived in terms of the varying Sf-spd hybridization. The non-magnetic ground state of URuAl and URuGa reflects more delocalized 5f states due to a stronger 5f-4d hybridization than in the ferromagnetic Rh compounds. The low temperature anomalies in the x(T) curves of the Ru compounds can be attributed to spin fluctuations. In URuAl, we have observed that the spin fluctuations are suppressed by sufficiently high magnetic fields. In both systems, when Ru is substituted by Rh, the large negative values of 0, (which may be tentatively taken as the characteristic spin-fluctuation temperature) are drastically reduced reflecting reduction of the spin-fluctuation energy. Both systems become ferromagnetic at nearly the same Rh concentration (x 2: 0.23). Surprisingly, nearly no change in the specific heat y values has been observed in the crossover region. Both T, and the uranium magnetic moment increase with increasing Rh content, reflecting the further reduced 5f-4d hybridization. The ordering temperature of the Al compounds reaches a maximum value at x 2: 0.6 and then decreases with increasing x. Before discussing this effect let us consider the geometry of the ZrNiAl-type structure and the possible interactions. The structure consists of U-T and T-X basal-
and magnetism in lJ(Ru, Rh)X
167
plane layers alternating along the hexagonal axis. In magnetically ordered compounds, magnetic moments are confined to the c-axis direction by a strong anisotropy due to a much stronger interuranium coupling within the basal plane (in which the 5f states and the d states of transition metal atoms are strongly hybridized) than along the c-axis. Magnetic structures consisting of ferromagnetic basal-plane sheets indicate a strong ferromagnetic interaction within the U-T layer [7]. The intersheet coupling (across T-X layers) is much weaker and determines, finally, whether the magnetic ordering is ferro- or antiferromagnetic. The experimental data known so far [5,7] can be qualitatively understood within a simple heuristic picture supposing that the 5f-d (d states of the T atoms in T-X layers) hybridization yields a ferromagnetic (F) component of the intersheet interactions, whereas the 5f-p (p states of X atoms) hybridization mediates an AF contribution. Then AF ordering, usually observed in the weak 5f-d hybridization limit (e.g. UNIX, UPdIn), is a consequence of prevailing AF coupling, whereas ferromagnetism appears for a stronger 5f-d hybridization (UCoX, URhX where the F component dominates). In this framework we can also explain the decrease of T, in URu, _,Rh,Al at higher x values. Since the 5f-4d hybridization weakens with increasing x, the F component of the intersheet interaction becomes comparable (around x = 0.6) to the component (mediated by the 5f3p hybridization) and, consequently, T, is reduced. This effect is not observed in the Ga system which is probably due to the fact that the 5f-4p hybridization is weaker than the 5f-3p hybridization in Al compounds.
Acknowledgements
This work is part of the research program on the Stichting voor Fundamenteel Ondezoek der Materie (FOM), which is financially supported by the Nederlandse organisatie voor Wetenschappelijk Onderzoek (NWO). Part of the work of V.S. has been supported by the Alexander von Humboldt Foundation.
168
V. Sechovsky et al. I Hybridization
References [l]
A.E. Dwight, in: Developments in the Structural Chemistry of Alloy Phases, ed. B.C. Giessen (Plenum, New York 1969) p. 181. [2] V. Sechovsky and L. Havela, Intermetallic compounds of actinides, in: Ferromagnetic Materials, eds. E.P. Wohlfarth and K.H.J. Buschow (North-Holland, Amsterdam 1988) pp. 309-491 and references therein. [3] V. Sechovsky, L. Havela, F.R. de Boer, J.J.M. Franse, P.A. Veenhuizen, J. Sebek, J. Stehno and A.V. Andreev, Physica B 142 (1986) 283.
and magnetism in U(Ru, Rh)X [4] P.A. Veenhuizen, F.R. de Boer, A.A. Menovsky, V. Sechovsky and L. Havela, J. de Phys. 49 (1988) C8-485. [5] V. Sechovsky, L. Havela, P. Nozar, E. Briick, F.R. de Boer, A.A. Menovsky, K.H.J. Buschow and A.V. Andreev, Physica B 163 (1990) 103. [6] P.A. Veenhuizen, J.C.P. Klaasse, F.R. de Boer, V. Sechovsky and L. Havela, J. Appl. Phys. 63 (1988) 3064. [7] V. Sechovsky and L. Havela, Proc. ICM’91, J. Magn. Magn. Mater. 104-107 (1992) 7.
PHY!ltCA 1
164-168
Hybridization
and magnetism
in U(Ru, Rh)X, X = Al, Ga
V. Sechovsky’, L. Havela”, F.R. de Boerb, P.A. Veenhuizen’, K. Sugiyama”, T. Kuroda’, E. Sugiura’, M. One’, M. DateC and A. Yamagishi’ “Department of Metal Physics, Charles University, Ke Karlovu 5, CS-12116 Prague 2, Czechoslovakia ‘Van der Waals-Zeeman Laboratory, University of Amsterdam, Valckenierstraat 65, 1018 XE Amsterdam, The Netherlands ‘Department of Physics, Osaka University, Toyonaka, Osaka 560, Japan
Results of magnetic studies of pseudoternary U(Ru, Rh)Al and U(Ru, 5f-4d hybridization with increasing Rh content is reflected in a gradual behaviour in URuX to ferromagnetism in URhX. The huge uniaxial anisotropic 5f-ligand hybridization.
1. Introduction URuAl, URuGa, URhAl and URhGa crystallize in the hexagonal ZrNiAl-type structure [l]. URhAl and URhGa are ferromagnetic below T, = 27 and 41 K, respectively [2]. URuAl and URuGa remain paramagnetic down to 20 mK [3]. Below 100 K, their magnetic susceptibilities deviate significantly from the high temperature Curie-Weiss behaviour. The JY(T) curve of URuAl exhibits a broad maximum at 50 K whereas a plateau and a low temperature upturn are found for URuGa [3]. These anomalies are reminiscent of the behaviour of the spin fluctuation materials UPt, and UAl,, respectively. Studies of URuAl and URhAl single crystals proved strong uniaxial magnetic anisotropy [4] which is common for UTX (T = transition metal, X = p-metal) compounds with the same structure [5]. In order to follow the transition from the non-magnetic state in URuX to ferromagnetism in URhX, we studied the magnetic behaviour of a number of pseudoternary compounds from the series URu,_,Rh,Al and URu,-.Rh,Ga. Results obtained on URu,_,Rh,Al [4] demonstrated a gradual reduction of the characteristic spin fluctuation energy with increasing Rh content, 0921-4526/92/$05.00
0
1992 - Elsevier
Science
Publishers
Rh)Ga systems are presented. Reduction of the transition from paramagnetic (spin fluctuation) magnetic anisotropy can be attributed to the
leading to ferromagnetism for x 2 0.23. Here, we compare this behaviour with results obtained on the analogous system U(Ru, Rh)Ga.
2. Experimental Polycrystalline samples of URu,_,Rh,Ga compounds have been prepared by arc melting under an argon atmosphere. All samples were single phase with the ZrNiAl-type structure. The lattice constants a and c vary almost linearly with x between those of URuGa, a = 707.6 pm, c =381.8pm, and URhGa, a =700.6pm, c= 394.5 pm. The magnetic susceptibility was measured on bulk samples in a SHE squid magnetometer in the temperature range 5-300 K. Magnetization curves at 4.2 K in fields B d 35 T were measured in the High Field Installation at the University of Amsterdam. Measurements of URuAl up to 60 T were performed in the High Field Installation at Osaka University. The magnetization was measured on two kinds of fine-powder samples: (a) loose powder grains which are oriented by the maximum magnetic field (free powder). (b) powder consisting of randomly oriented grains fixed by frozen alcohol (fixed powder).
B.V. All rights
reserved
V. Sechovsky et al. I Hybridization
and magnetism in U(Ru, Rh)X
165
On the free powder, we obtain the magnetization (M,,) in the easy magnetization direction, provided that the powder particles are single crystals and that they are fully oriented by the applied magnetic field. The fixed powder has the magnetization (Mrnd) of an ideal polycrystal. T200 ’
3. Results and discussion
t
The temperature dependence of the magnetic susceptibility x(T) of URuGa (fig. 1) at high temperatures (T > 100 K) can be described by a Curie-Weiss law including a temperature-independent contribution x0 = 1 x lo-’ m3/mol, x = CI(T-
0,) +x0 )
(1)
with 0, = -192 K. By gradual Rh substitution (fig. l), the Curie-Weiss behaviour is extended to lower temperatures and an upturn develops in the low temperature plateau of the x(T) curve. Moreover, the originally large negative Or, values are reduced very fast (fig. 2). Ferromagnetism occurs for x > 0.2 where the 0, values become 2 .
-250 ’ 0.0
0.2
0.4
0.6 X
Fig. 2. Concentration dependences of the paramagnetic Curie temperature 0, of URu,-,Rh,AI and URu,-,Rh,Ga. The lines are guides to the eye.
positive and both 0, and the ordering temperature T, (see fig. 3) increase with further increasing x. The magnetization curves of URuGa and URuAl at 4.2 K are compared in fig. 4. The high-field upturn in the M(B) curve of URuAl obtained in measurements up to 35 T has been reported previously [3,6]. The free powder measurement extended to 60 T reveals that aM/a B has a maximum at about 25 T and that the magnetization tends to saturate at higher fields. Linear extrapolation of M versus 1 lB to l/B = 0 yields an estimate of the saturated magnetic 50
. .
E
\
.
mE ?O ;I
I 1.0
0.8
URu,_,Rh,Ga
. 5
i
0
40 /*
30
r:
1.5
z
8
” t+ 20
0 0.0
0 0
50
150
100 TIKI
Fig. 1. Temperature dependence of the susceptibility of Uru,_,Rh,Ga for the concentrations x = 0 (O), 0.1 (0), 0.2 (A) and 0.3 (A). The lines represent Curie-Weiss fits.
0.2
0.4
0.6
0.8
1.0
X Fig.
3. Concentration dependences of 7-c (circles) and (triangles) of U(Ru,_,Rh,)AI (open symbols) and U(Ru,_,Rh,)Ga (full symbols). The lines are guides to the eye.
Mt
V. Sechovsky et al. I Hybridization and magnetism in U(Ru,
166
r
06
Rh)X
trapolating M versus B to B = 0 T) increases with increasing Rh content (fig. 3). Comparison of the free powder and the fixed powder magnetizations (figs. 5 and 6, respectively) reveals strong magnetic anisotropy in all URu,_,Rh,Ga compounds. In case of uniaxial anisotropy,
0.5
IO
30
20
40
50
60
B (I.1
Fig. 4. Magnetization curves of URuAl and URuGa at 4.2 K measured on field-oriented powder and fixed powder.
moment of 0.84&f.u. The free powder M(B) curve of URuGa also displays an upturn (but much less pronounced) above 20 T. Fields higher than 35 T are needed to study further details of this anomaly. The M(B) curves of all URu, _,Rh,Ga compounds measured on free powders (fig. 5) demonstrate a development of magnetism similar to that in URu,_,Rh,Al [6]. The slight upturn persists in URu,.,Rh,, 1Ga. The magnetization is enhanced with increasing x and, for x > 0.2, we observe ferromagnetic ordering. The spontaneous magnetization M’, (estimated by ex0.7
M,, = M; + Bxc ,
(2)
M rnd = M;l2 + Bxc/3 + 2B~~.~/3,
(3)
provided that the susceptibilities (x = dMld B) xc (along the c-axis) and xa,b (in the basal plane) are field independent. Then we can derive the anisotropic parameters xc, xa,b and Mi from powder data. In fig. 7, we can see that for ferromagnetic compounds M,,= 2M,,, in B = OT, which indicates uniaxial anisotropy. For paramagnets as URuGa, M',= 0 and the difference 3M,,, - M,, = ~Bx~,~. The M',results of U(Ru, Rh)Ga are displayed in fig. 3. While the X a7b values are almost concentration-independent across the series (2.8 x lo-’ m3/mol in URuGa, 2.1 x lop8 m3/mol in URhGa), the easy axis susceptibilities are much larger for paramagnetic compounds (5.1 X lo-’ m3/mol in URuAl) than in the ferromagnetic ones (2.4 x lo-* m3/mol in URhGa). The development of magnetism in UTX compounds, as in many other actinide intermetallics 1.5
X= 1.0
1 X=
0.6
0
IO
20
30
40
13CT)
Fig. 5. Magnetization curves of URu,_,Rh,Ga at 4.2 K, for different compositions, measured on field-oriented powders. The lines are guides to the eye.
B (‘0
Fig. 6. Magnetization curves of polycrystalline URu,_,Rh,Ga (fixed powder) at 4.2 K for different compositions. The lines are guides to the eye.
V. Sechovsky et al. I Hybridization
URhGa
o,ov 0
IO
’ 20
30
40
B CT)
Fig. 7. Comparison of magnetization curves of URuGa, URu,, ,Rh, ,Ga and URhGa at 4.2K measured on fieldoriented powder and fixed powder. The lines are guides to the eye.
[5,7], can be conceived in terms of the varying Sf-spd hybridization. The non-magnetic ground state of URuAl and URuGa reflects more delocalized 5f states due to a stronger 5f-4d hybridization than in the ferromagnetic Rh compounds. The low temperature anomalies in the x(T) curves of the Ru compounds can be attributed to spin fluctuations. In URuAl, we have observed that the spin fluctuations are suppressed by sufficiently high magnetic fields. In both systems, when Ru is substituted by Rh, the large negative values of 0, (which may be tentatively taken as the characteristic spin-fluctuation temperature) are drastically reduced reflecting reduction of the spin-fluctuation energy. Both systems become ferromagnetic at nearly the same Rh concentration (x 2: 0.23). Surprisingly, nearly no change in the specific heat y values has been observed in the crossover region. Both T, and the uranium magnetic moment increase with increasing Rh content, reflecting the further reduced 5f-4d hybridization. The ordering temperature of the Al compounds reaches a maximum value at x 2: 0.6 and then decreases with increasing x. Before discussing this effect let us consider the geometry of the ZrNiAl-type structure and the possible interactions. The structure consists of U-T and T-X basal-
and magnetism in lJ(Ru, Rh)X
167
plane layers alternating along the hexagonal axis. In magnetically ordered compounds, magnetic moments are confined to the c-axis direction by a strong anisotropy due to a much stronger interuranium coupling within the basal plane (in which the 5f states and the d states of transition metal atoms are strongly hybridized) than along the c-axis. Magnetic structures consisting of ferromagnetic basal-plane sheets indicate a strong ferromagnetic interaction within the U-T layer [7]. The intersheet coupling (across T-X layers) is much weaker and determines, finally, whether the magnetic ordering is ferro- or antiferromagnetic. The experimental data known so far [5,7] can be qualitatively understood within a simple heuristic picture supposing that the 5f-d (d states of the T atoms in T-X layers) hybridization yields a ferromagnetic (F) component of the intersheet interactions, whereas the 5f-p (p states of X atoms) hybridization mediates an AF contribution. Then AF ordering, usually observed in the weak 5f-d hybridization limit (e.g. UNIX, UPdIn), is a consequence of prevailing AF coupling, whereas ferromagnetism appears for a stronger 5f-d hybridization (UCoX, URhX where the F component dominates). In this framework we can also explain the decrease of T, in URu, _,Rh,Al at higher x values. Since the 5f-4d hybridization weakens with increasing x, the F component of the intersheet interaction becomes comparable (around x = 0.6) to the component (mediated by the 5f3p hybridization) and, consequently, T, is reduced. This effect is not observed in the Ga system which is probably due to the fact that the 5f-4p hybridization is weaker than the 5f-3p hybridization in Al compounds.
Acknowledgements
This work is part of the research program on the Stichting voor Fundamenteel Ondezoek der Materie (FOM), which is financially supported by the Nederlandse organisatie voor Wetenschappelijk Onderzoek (NWO). Part of the work of V.S. has been supported by the Alexander von Humboldt Foundation.
168
V. Sechovsky et al. I Hybridization
References [l]
A.E. Dwight, in: Developments in the Structural Chemistry of Alloy Phases, ed. B.C. Giessen (Plenum, New York 1969) p. 181. [2] V. Sechovsky and L. Havela, Intermetallic compounds of actinides, in: Ferromagnetic Materials, eds. E.P. Wohlfarth and K.H.J. Buschow (North-Holland, Amsterdam 1988) pp. 309-491 and references therein. [3] V. Sechovsky, L. Havela, F.R. de Boer, J.J.M. Franse, P.A. Veenhuizen, J. Sebek, J. Stehno and A.V. Andreev, Physica B 142 (1986) 283.
and magnetism in U(Ru, Rh)X [4] P.A. Veenhuizen, F.R. de Boer, A.A. Menovsky, V. Sechovsky and L. Havela, J. de Phys. 49 (1988) C8-485. [5] V. Sechovsky, L. Havela, P. Nozar, E. Briick, F.R. de Boer, A.A. Menovsky, K.H.J. Buschow and A.V. Andreev, Physica B 163 (1990) 103. [6] P.A. Veenhuizen, J.C.P. Klaasse, F.R. de Boer, V. Sechovsky and L. Havela, J. Appl. Phys. 63 (1988) 3064. [7] V. Sechovsky and L. Havela, Proc. ICM’91, J. Magn. Magn. Mater. 104-107 (1992) 7.