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Magnetic behavior of lower hydrides of Y6Mn23 and Th6Mn23
Journal of the Less-Common
MAGNETIC Th&&s S. K. MALIK*,
Department (Received
Metals, 98 (1984)
BEHAVIOR
OF LOWER HYDRIDES
G. T. BAYER,
E. B. BOLTICH
of Chemistry,
August
109
109 - 114
OF Y&In,, AND
and W. E. WALLACE
University of Pittsburgh, Pittsburgh, PA 15260 (U.S.A.)
11,1983)
Summary Earlier studies have revealed dramatic changes in the magnetic behavior of Y,Mn2s and Th,Mn2, on hydrogen absorption. Y,Mn,, is ferrimagnetically ordered while Y,Mn,,H,,, exhibits antiferromagnetic ordering. In contrast, Th,Mn2, is a Pauli paramagnet while Th,Mn2sHas0 is ferrimagnetically ordered. We have now examined the magnetic behavior of lower hydrides of Y,Mn,, and Th&In2,. It is observed that magnetic ordering, possibly of the ferrimagnetic type, still persists in Y,Mn23Ha:10. This material also shows anomalies in magnetization at low temperature. Th,Mn2sH1,., is observed to be magnetically ordered with a low Curie temperature and a small magnetic moment per formula unit.
1. Introduction Many rare earth intermetallic compounds with transition elements absorb large quantities of hydrogen [ 11. The effect of absorbed hydrogen on the magnetic properties of these compounds is of great fundamental interest. It has been shown earlier from this laboratory that the magnetic behavior of altered on hydrogen absorption [2]. Y&In2, and Th,Mn2, is dramatically The compound Y,J4n23 is ferrimagnetically ordered with a Curie temperature Tc of about 500 K and a bulk magnetization of 11.3 pa (formula unit)-‘. After hydrogenation to the composition Y6Mn23HE;25,the compound did not show any ferromagnetic or ferrimagnetic ordering and was presumed to be a paramagnet. However, a small peak in the magnetization versus temperature curve was observed at about 160 K. It was subsequently shown from neutron diffraction studies that YJ4n23Ha22 orders antiferromagnetically with the NCel temperature coincident with the peak in the bulk magnetization curve [3]. In contrast, Th,MnZ3 which is isostructural with Y,Mn2s is a Pauli
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address:
Tata
Institute
of
Fundamental
@ Elsevier
Research,
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in The Netherlands
110
paramagnet, but ThJ4n2sHxs0 is found to order magnetically with a Curie temperature of 329 K. These studies on 6:23 compounds of yttrium and thorium with manganese were carried out on samples containing large amounts of hydrogen (hydrogenated to full capacity at room temperature and high pressures). Recently, Smith has determined the pressure-composition isotherms of Y6Mn2a-H2 [4] and Th&n2a- H2 [S] systems. The yttrium-containing system at 0 “C showed a monotonic rise in pressure with hydrogen composition, i.e. there was no plateau. The thori~~ontaining system has a welldefined plateau at the same temperature. In the light of earlier magnetic studies on fully hydrogenated samples, it is of interest to study the magnetic behavior of lower hydrides of these compounds, particularly to explore the dependence of magnetic ordering on hydrogen content. In this paper we report the results of ~a~etization studies on Y&In&,,, and Th&In23H17.6 in the temperature range 4.2 - 300 K. In the following we find that magnetic order (possibly of the ferrimagnetic type) still persists in going from Y&In2s to Y&ln23Hwi10, while Th6Mn23H17.6 already shows the onset of magnetic ordering with low moment and low Curie temperature in contrast with the Pauli paramagnetic behavior of Th&&. 2. Experimental
details
Y,Mn,, and Th,Mn,, were prepared by melting together stoicbiometric amounts of yttrium or thorium and manganese, with a small excess of manganese, in a water-cooled copper boat, under a purified argon atmosphere. A 10 kW r.f. induction furnace was used for the melting. The stated purities of the elements used with respect to their metallic content were as follows: 99.9% Mn, 99.9% Y and 99.99% Th (crystal bar). It was observed that formation of the desired compounds was facilitated by premelting the manganese several times, which possibly reduced the content of non-metallic impurities. Y,Mn,, and Th,Mn,, were annealed for 1 h immediately below the solidification temperature in the induction furnace to ensure homogeneity. Powder X-ray diffraction patterns indicated the annealed samples to be single-phase materials. The pressure-composition isotherms were obtained using approximately 2.5 g of Thanz, at 24 “C and approximately 2.5 g of Y&In,, at 23 “C. The samples were activated by heating for 1 h under vacuum at 200 “C. A stainless steel system with Bourdon tube type of gauges was used for the equilibrium points above atmospheric pressure. To obtain each subsequent lower equilibrium pressure point, an increment of 100 ml or less of hydrogen gas was removed by displacing water in a gas buret. For the equilibrium points below atmosphe~c pressure, increments of hydrogen were removed using a glass vacuum system equipped with a Toepler pump. Time periods of 20 min or greater were required in order to establish equilibrium at each pressure. The Beattie-Bridgeman equation of state for hydrogen was employed in the calculation of equilibrium points.
111
After completion of the desorption isotherm, hydrogen was admitted to the system in the desired amount, and then SOZ was introduced into the system to poison the surface of the hydride 161. The hydride was then taken out, and a portion for X-ray diffraction studies and the remainder were immediately transferred to the sample holder used for the magnetic measurements. The hydrides had the stoichiometry Y&n2a9.97 and By X-ray diffraction they were observed to be single-phase Th~n2~Hl7.~. materials. However, another hydride of an yttrium-containing compound with the stoichiometry Y6MnZ3HZ1z was found by this technique to consist of two phases. M~etization studies were carried out in the temperature range 4.2 300 K in applied fields up to 20 kOe using the Faraday method. Magnetization versus applied field isotherms were also obtained at 4.2 K for both the hydrides.
3. Results and discussion 3.1. ~ess~re-composition isotherms and crystalio~a~~~c features The compounds Y,Mn*s and Th&lnz, are isostructural and crystallize in the f.c.c. structure space group Fm3m ]7]. Pressure-composition isotherms for Y&n 2s-H2 (Fig. 1) and for Th~Mn*~-H~ (Fig. 2) were obtained at 23 “C and 24 “C respectively in the pressure range from about 10-s to
x mole H /mole
Alloy
X mole
H / mole
Fig. 1. Pressure-composition
isotherm for the system Y&Snz+--H2 at 23 “C.
Fig. 2. Pressure-composition
isotherm for the system Th&Inz3-H1 at 24 “C.
Alloy
112
30 atm. The maximum absorption in the yttrium-containing system corresponds to the formula Y6Mn23H23.7 at 30 atm. lJnlike the results of Smith alluded to above, there is a narrow plateau region around 12 hydrogen atoms per formula unit. A sample of the stoiehiometry Y6Mn23H’312was examined by X-rays and found, as noted above, to be a two-phase material. A twophase system is, of course, expected if the pressure-composition curve exhibits a plateau. For the magnetic studies the hydride with the composition Y6Mn23H9_97 (designated hereafter as Y~n~~~~~~) was employed. As noted above, this was found to be a single-phase cubic material. Hydrogen absorption results in expansion of the lattice. The lattice parameters are as follows: for Y&&i 23, a = 12.458 Ir\; for Y,JvlnZ3HWi0, a = 12.565 A; for Y&lnZsHZ4, (I = 12.842 A. The maximum absorption for Th,Mnzs corresponds to Th,Mn,sH29,s at a hydrogen pressure of about 30 atm. In contrast with the yttrium~ont~n~g system, the Th~Mn~~-H~ system shows a welldefined plateau in the region from 21 to 28 hydrogen atoms per formula unit. The difference between the yttriumand the thorium-containing systems as regards the amount of hydrogen absorbed and the shape of the pressure-composition isotherms is most probably a consequence of the differing electronic structure of the two systems, which can be inferred from their differing magnetic behavior summarized in Section 1. The lattice parameters of the thorium-containing system are as follows: for Th,Mnzs, a = 12.480 A; for Th&in23H1,_6, a = 12.966 A; for ThgMn23H30, a = 13.259 8.
Each unit cell of Y,Mn,, (or Th&n,,) contains a unique yttrium (thorium) site and four manganese sites (4b, 24d, 32fi and 32f,). The magnetic structure of this compound is such that b and d site manganese moments are coupled parallel to each other, and the resultant moment is coupled antiparallel to the two f site manganese moments [ 81. After hydrogenation (deuteration), as noted above, the compound Y&fn23Hm:24 exhibits antiferromagnetic ordering with a NQel temperature TN = 160 K 123. Neutron diffraction studies on Y&lnZ3Des at 78 and 4.2 K reveal that only two of the four original manganese sites participate in long-range magnetic order. The other two manganese sites appear to have no moment [ 91. Figure 3 shows the magnetization uersus applied field isotherms for at 4.2 and 245 K. Both these curves are characteristic of a Y6Mn&Lo magnetically ordered system. The magnetization at 4.2 K and in a 20 kOe applied field corresponds to 4.5 pa (formula unit)-‘, which is considerably smaller than the value of 11.3 /~a (formula unit)-’ for YJ4n23. This indicates that either the individual manganese moments or their coupling scheme have been influenced by absorption of ten hydrogen atoms per formula unit, although not to such an extent as in Y&n,,H,,. Commandre et al. [lo] also observed reduced magnetization in YeMnZ3D9 compared with that in YsMn23. Figure 4 shows the variation in magnetization of Y6Mn2sHmio as a function of temperature in two different applied fields. These data show that YbMn2sHei0
\
:3 5
2
2451(
i/-
6
z k
. __._.__._._ ._.*_.-. -_--
! 2
-1 .
/ *
1 :
Of
0
I
I
I
I
4
0
12
16
Appl!ed
Field
(hoe)
I 20
T (K)
Fig. 3. Magnetization us. applied field for Y&lnz3Hs10 at 4.2 and 245 K. Fig. 4. Magnetization us. temperature for Y&ln23H c1o at two different applied fields: X, 20 kOe; 0, 8 kOe. The inset shows on an expanded scale the magnetization us. temperature range 4.2 - 100 K.
is magnetically ordered at room temperature, and the Curie point must lie above 300 K. An anomaly in the magnetization is observed (Fig, 4, inset) with a sharp but small drop at 30 K followed by a broad maximum at 75 K. In the light of the neutron diffraction studies on the hydride of Y,Mn2s [9] it is probable that the anomaly represents either (i) a change in magnetic structure or (ii) some type of compensation point between a particular group of sublattices. 3.3. Magnetic behavior of Th,Mnz3 hydrides As remarked earlier, the compound Th$Jnz, is a Pauli paramagnet, while Th,Mn,,H,,,, is magnetically ordered with an extrapolated Curie temperature of 329 K and a moment of 18.4 pa (formula Unit)-’ [2]. Neutron diffraction studies on Th@-i2&s,, indicate that all the manganese moments are coupled parallel except the moment at the b site, which is coupled antiparallel to the remaining manganese moments [ 111. The individual manganese moments are much smalier in Th&In,sD,s, than those in Y&ln2sDe4. Figure 5 shows the magnetization of Th&lnzsH1,.6 versus the field isotherm at 4.2 K (inset) and magnetization versus temperature at a 20 kOe applied field. The hydride appears to be magnetically ordered with a Curie temperature of 24 K and a moment of 0.93 pg (formula unit))’ at 4.2 K and a 20 kOe field. The magnetization does not show saturation behavior, behaving as if a paramagnetic contribution is present. Perhaps the band magnetism from the manganese d electrons gives rise to this behavior. Neutron diffraction studies have failed to detect magnetic ordering in Th,MnZ,D,,, but there appears to be a magnetic contribution to the intensities of the lines in the neutron diffraction pattern [ll]. Our studies reveal that Th&InZ,H1,.6 is indeed magnetically ordered but has a very low moment per manganese ion. The low manganese moments may be responsible for the failure to detect magnetic ordering by neutron scattering experiments.
114
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0.6
0.6
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-
0.4 0.2
0.4 _\
0
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,
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,
I::lj:
0
4
8
12
16
20
H
01
0
I
100
1
J
200
300
T (K)
Fig. 5. Magnetization us. temperature for TheMn2sHI*r7.e at a 20 kOe applied inset shows the magnetization us. applied field isotherm at 4.2 K.
field.
The
Acknowledgments The magnetic studies were assisted by a grant from the Army Research Office. The pressure-composition work was assisted by the National Science Foundation through Grant 8208048.
References 1 W. E. Wallace, R. S. Craig and V. U. S. Rao, Adu. Chem. Ser., 186 (1980) 207. 2 S. K. Malik, T. Takeshita and W. E. Wallace, Solid State Commun., 23 (1977) 599. 3 K. Hardman, J. J. Rhyne, H. K. Smith, W. E. Wallace and S. K. Malik, J. Appl. Phys., 52 (1981) 2070. 4 H. K. Smith, unpublished data, 1983, 5 H. K. Smith, Ph.D. Thesis, University of Pittsburgh, 1983. 6 D. M. Gualtieri, K. S. V. L. Narasimhan and T. Takeshita, J. Appl. Phys., 47 (1976). 3432. 7 J. V. Florio, R. E. Rundle and A. I. Snow, Acta Crystallogr., 5 (1952) 449. 8 A. Delapalme, J. Desportes, R. Lemaire, K. Hardman and W. J. James, J. Appl. Phys., 50 (1979) 1987. 9 K. Hardman-Rhyne, J. J. Rhyne, E. Prince, C. Crowder and W. J. James, Phys. Rev. B, to be published. 10 M. Commandre, D. Fruchart, A. Roualt, D. Sauvage, C. B. Shoemaker and D. P. Shoemaker, J. Phys. (Paris), 40 (1979) L-639. 11 K. Hardman-Rhyne, H. K. Smith and W. E. Wallace, J. Less-Common Met., 96 (1984) 201.
MAGNETIC Th&&s S. K. MALIK*,
Department (Received
Metals, 98 (1984)
BEHAVIOR
OF LOWER HYDRIDES
G. T. BAYER,
E. B. BOLTICH
of Chemistry,
August
109
109 - 114
OF Y&In,, AND
and W. E. WALLACE
University of Pittsburgh, Pittsburgh, PA 15260 (U.S.A.)
11,1983)
Summary Earlier studies have revealed dramatic changes in the magnetic behavior of Y,Mn2s and Th,Mn2, on hydrogen absorption. Y,Mn,, is ferrimagnetically ordered while Y,Mn,,H,,, exhibits antiferromagnetic ordering. In contrast, Th,Mn2, is a Pauli paramagnet while Th,Mn2sHas0 is ferrimagnetically ordered. We have now examined the magnetic behavior of lower hydrides of Y,Mn,, and Th&In2,. It is observed that magnetic ordering, possibly of the ferrimagnetic type, still persists in Y,Mn23Ha:10. This material also shows anomalies in magnetization at low temperature. Th,Mn2sH1,., is observed to be magnetically ordered with a low Curie temperature and a small magnetic moment per formula unit.
1. Introduction Many rare earth intermetallic compounds with transition elements absorb large quantities of hydrogen [ 11. The effect of absorbed hydrogen on the magnetic properties of these compounds is of great fundamental interest. It has been shown earlier from this laboratory that the magnetic behavior of altered on hydrogen absorption [2]. Y&In2, and Th,Mn2, is dramatically The compound Y,J4n23 is ferrimagnetically ordered with a Curie temperature Tc of about 500 K and a bulk magnetization of 11.3 pa (formula unit)-‘. After hydrogenation to the composition Y6Mn23HE;25,the compound did not show any ferromagnetic or ferrimagnetic ordering and was presumed to be a paramagnet. However, a small peak in the magnetization versus temperature curve was observed at about 160 K. It was subsequently shown from neutron diffraction studies that YJ4n23Ha22 orders antiferromagnetically with the NCel temperature coincident with the peak in the bulk magnetization curve [3]. In contrast, Th,MnZ3 which is isostructural with Y,Mn2s is a Pauli
*Permanent 400005, India. 0022-5088/84/$3.00
address:
Tata
Institute
of
Fundamental
@ Elsevier
Research,
Sequoia/Printed
Colaba,
Bombay
in The Netherlands
110
paramagnet, but ThJ4n2sHxs0 is found to order magnetically with a Curie temperature of 329 K. These studies on 6:23 compounds of yttrium and thorium with manganese were carried out on samples containing large amounts of hydrogen (hydrogenated to full capacity at room temperature and high pressures). Recently, Smith has determined the pressure-composition isotherms of Y6Mn2a-H2 [4] and Th&n2a- H2 [S] systems. The yttrium-containing system at 0 “C showed a monotonic rise in pressure with hydrogen composition, i.e. there was no plateau. The thori~~ontaining system has a welldefined plateau at the same temperature. In the light of earlier magnetic studies on fully hydrogenated samples, it is of interest to study the magnetic behavior of lower hydrides of these compounds, particularly to explore the dependence of magnetic ordering on hydrogen content. In this paper we report the results of ~a~etization studies on Y&In&,,, and Th&In23H17.6 in the temperature range 4.2 - 300 K. In the following we find that magnetic order (possibly of the ferrimagnetic type) still persists in going from Y&In2s to Y&ln23Hwi10, while Th6Mn23H17.6 already shows the onset of magnetic ordering with low moment and low Curie temperature in contrast with the Pauli paramagnetic behavior of Th&&. 2. Experimental
details
Y,Mn,, and Th,Mn,, were prepared by melting together stoicbiometric amounts of yttrium or thorium and manganese, with a small excess of manganese, in a water-cooled copper boat, under a purified argon atmosphere. A 10 kW r.f. induction furnace was used for the melting. The stated purities of the elements used with respect to their metallic content were as follows: 99.9% Mn, 99.9% Y and 99.99% Th (crystal bar). It was observed that formation of the desired compounds was facilitated by premelting the manganese several times, which possibly reduced the content of non-metallic impurities. Y,Mn,, and Th,Mn,, were annealed for 1 h immediately below the solidification temperature in the induction furnace to ensure homogeneity. Powder X-ray diffraction patterns indicated the annealed samples to be single-phase materials. The pressure-composition isotherms were obtained using approximately 2.5 g of Thanz, at 24 “C and approximately 2.5 g of Y&In,, at 23 “C. The samples were activated by heating for 1 h under vacuum at 200 “C. A stainless steel system with Bourdon tube type of gauges was used for the equilibrium points above atmospheric pressure. To obtain each subsequent lower equilibrium pressure point, an increment of 100 ml or less of hydrogen gas was removed by displacing water in a gas buret. For the equilibrium points below atmosphe~c pressure, increments of hydrogen were removed using a glass vacuum system equipped with a Toepler pump. Time periods of 20 min or greater were required in order to establish equilibrium at each pressure. The Beattie-Bridgeman equation of state for hydrogen was employed in the calculation of equilibrium points.
111
After completion of the desorption isotherm, hydrogen was admitted to the system in the desired amount, and then SOZ was introduced into the system to poison the surface of the hydride 161. The hydride was then taken out, and a portion for X-ray diffraction studies and the remainder were immediately transferred to the sample holder used for the magnetic measurements. The hydrides had the stoichiometry Y&n2a9.97 and By X-ray diffraction they were observed to be single-phase Th~n2~Hl7.~. materials. However, another hydride of an yttrium-containing compound with the stoichiometry Y6MnZ3HZ1z was found by this technique to consist of two phases. M~etization studies were carried out in the temperature range 4.2 300 K in applied fields up to 20 kOe using the Faraday method. Magnetization versus applied field isotherms were also obtained at 4.2 K for both the hydrides.
3. Results and discussion 3.1. ~ess~re-composition isotherms and crystalio~a~~~c features The compounds Y,Mn*s and Th&lnz, are isostructural and crystallize in the f.c.c. structure space group Fm3m ]7]. Pressure-composition isotherms for Y&n 2s-H2 (Fig. 1) and for Th~Mn*~-H~ (Fig. 2) were obtained at 23 “C and 24 “C respectively in the pressure range from about 10-s to
x mole H /mole
Alloy
X mole
H / mole
Fig. 1. Pressure-composition
isotherm for the system Y&Snz+--H2 at 23 “C.
Fig. 2. Pressure-composition
isotherm for the system Th&Inz3-H1 at 24 “C.
Alloy
112
30 atm. The maximum absorption in the yttrium-containing system corresponds to the formula Y6Mn23H23.7 at 30 atm. lJnlike the results of Smith alluded to above, there is a narrow plateau region around 12 hydrogen atoms per formula unit. A sample of the stoiehiometry Y6Mn23H’312was examined by X-rays and found, as noted above, to be a two-phase material. A twophase system is, of course, expected if the pressure-composition curve exhibits a plateau. For the magnetic studies the hydride with the composition Y6Mn23H9_97 (designated hereafter as Y~n~~~~~~) was employed. As noted above, this was found to be a single-phase cubic material. Hydrogen absorption results in expansion of the lattice. The lattice parameters are as follows: for Y&&i 23, a = 12.458 Ir\; for Y,JvlnZ3HWi0, a = 12.565 A; for Y&lnZsHZ4, (I = 12.842 A. The maximum absorption for Th,Mnzs corresponds to Th,Mn,sH29,s at a hydrogen pressure of about 30 atm. In contrast with the yttrium~ont~n~g system, the Th~Mn~~-H~ system shows a welldefined plateau in the region from 21 to 28 hydrogen atoms per formula unit. The difference between the yttriumand the thorium-containing systems as regards the amount of hydrogen absorbed and the shape of the pressure-composition isotherms is most probably a consequence of the differing electronic structure of the two systems, which can be inferred from their differing magnetic behavior summarized in Section 1. The lattice parameters of the thorium-containing system are as follows: for Th,Mnzs, a = 12.480 A; for Th&in23H1,_6, a = 12.966 A; for ThgMn23H30, a = 13.259 8.
Each unit cell of Y,Mn,, (or Th&n,,) contains a unique yttrium (thorium) site and four manganese sites (4b, 24d, 32fi and 32f,). The magnetic structure of this compound is such that b and d site manganese moments are coupled parallel to each other, and the resultant moment is coupled antiparallel to the two f site manganese moments [ 81. After hydrogenation (deuteration), as noted above, the compound Y&fn23Hm:24 exhibits antiferromagnetic ordering with a NQel temperature TN = 160 K 123. Neutron diffraction studies on Y&lnZ3Des at 78 and 4.2 K reveal that only two of the four original manganese sites participate in long-range magnetic order. The other two manganese sites appear to have no moment [ 91. Figure 3 shows the magnetization uersus applied field isotherms for at 4.2 and 245 K. Both these curves are characteristic of a Y6Mn&Lo magnetically ordered system. The magnetization at 4.2 K and in a 20 kOe applied field corresponds to 4.5 pa (formula unit)-‘, which is considerably smaller than the value of 11.3 /~a (formula unit)-’ for YJ4n23. This indicates that either the individual manganese moments or their coupling scheme have been influenced by absorption of ten hydrogen atoms per formula unit, although not to such an extent as in Y&n,,H,,. Commandre et al. [lo] also observed reduced magnetization in YeMnZ3D9 compared with that in YsMn23. Figure 4 shows the variation in magnetization of Y6Mn2sHmio as a function of temperature in two different applied fields. These data show that YbMn2sHei0
\
:3 5
2
2451(
i/-
6
z k
. __._.__._._ ._.*_.-. -_--
! 2
-1 .
/ *
1 :
Of
0
I
I
I
I
4
0
12
16
Appl!ed
Field
(hoe)
I 20
T (K)
Fig. 3. Magnetization us. applied field for Y&lnz3Hs10 at 4.2 and 245 K. Fig. 4. Magnetization us. temperature for Y&ln23H c1o at two different applied fields: X, 20 kOe; 0, 8 kOe. The inset shows on an expanded scale the magnetization us. temperature range 4.2 - 100 K.
is magnetically ordered at room temperature, and the Curie point must lie above 300 K. An anomaly in the magnetization is observed (Fig, 4, inset) with a sharp but small drop at 30 K followed by a broad maximum at 75 K. In the light of the neutron diffraction studies on the hydride of Y,Mn2s [9] it is probable that the anomaly represents either (i) a change in magnetic structure or (ii) some type of compensation point between a particular group of sublattices. 3.3. Magnetic behavior of Th,Mnz3 hydrides As remarked earlier, the compound Th$Jnz, is a Pauli paramagnet, while Th,Mn,,H,,,, is magnetically ordered with an extrapolated Curie temperature of 329 K and a moment of 18.4 pa (formula Unit)-’ [2]. Neutron diffraction studies on Th@-i2&s,, indicate that all the manganese moments are coupled parallel except the moment at the b site, which is coupled antiparallel to the remaining manganese moments [ 111. The individual manganese moments are much smalier in Th&In,sD,s, than those in Y&ln2sDe4. Figure 5 shows the magnetization of Th&lnzsH1,.6 versus the field isotherm at 4.2 K (inset) and magnetization versus temperature at a 20 kOe applied field. The hydride appears to be magnetically ordered with a Curie temperature of 24 K and a moment of 0.93 pg (formula unit))’ at 4.2 K and a 20 kOe field. The magnetization does not show saturation behavior, behaving as if a paramagnetic contribution is present. Perhaps the band magnetism from the manganese d electrons gives rise to this behavior. Neutron diffraction studies have failed to detect magnetic ordering in Th,MnZ,D,,, but there appears to be a magnetic contribution to the intensities of the lines in the neutron diffraction pattern [ll]. Our studies reveal that Th&InZ,H1,.6 is indeed magnetically ordered but has a very low moment per manganese ion. The low manganese moments may be responsible for the failure to detect magnetic ordering by neutron scattering experiments.
114
i.Or 0.8
0.6
0.6
M
-
0.4 0.2
0.4 _\
0
,
,
I
,
I::lj:
0
4
8
12
16
20
H
01
0
I
100
1
J
200
300
T (K)
Fig. 5. Magnetization us. temperature for TheMn2sHI*r7.e at a 20 kOe applied inset shows the magnetization us. applied field isotherm at 4.2 K.
field.
The
Acknowledgments The magnetic studies were assisted by a grant from the Army Research Office. The pressure-composition work was assisted by the National Science Foundation through Grant 8208048.
References 1 W. E. Wallace, R. S. Craig and V. U. S. Rao, Adu. Chem. Ser., 186 (1980) 207. 2 S. K. Malik, T. Takeshita and W. E. Wallace, Solid State Commun., 23 (1977) 599. 3 K. Hardman, J. J. Rhyne, H. K. Smith, W. E. Wallace and S. K. Malik, J. Appl. Phys., 52 (1981) 2070. 4 H. K. Smith, unpublished data, 1983, 5 H. K. Smith, Ph.D. Thesis, University of Pittsburgh, 1983. 6 D. M. Gualtieri, K. S. V. L. Narasimhan and T. Takeshita, J. Appl. Phys., 47 (1976). 3432. 7 J. V. Florio, R. E. Rundle and A. I. Snow, Acta Crystallogr., 5 (1952) 449. 8 A. Delapalme, J. Desportes, R. Lemaire, K. Hardman and W. J. James, J. Appl. Phys., 50 (1979) 1987. 9 K. Hardman-Rhyne, J. J. Rhyne, E. Prince, C. Crowder and W. J. James, Phys. Rev. B, to be published. 10 M. Commandre, D. Fruchart, A. Roualt, D. Sauvage, C. B. Shoemaker and D. P. Shoemaker, J. Phys. (Paris), 40 (1979) L-639. 11 K. Hardman-Rhyne, H. K. Smith and W. E. Wallace, J. Less-Common Met., 96 (1984) 201.