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Ferromagnetism in dilute ternary Pd(Fe, GD) alloys
Volume 44A, number 2
PHYSICS LETTERS
21 May 1973
FERROMAGNETISM IN DILUTE TERNARY Pd(Fe, Gd) ALLOYS J. CRANGLE Department of Physics, University of Sheffield, Sheffield S3 7RH, UK Received 16 April 1973 In (Pdo
997Feooo3)1_~Gd~ alloys the apparent magnetic moment of the polarized palladium solvent falls sharply with increasing x, and changes sign. The Curie temperature goes through a broad minimum at x 0.02.
Ferromagnetism occurs in dilute solutions of iron or cobalt in palladium [1—3].Giant magnetic moments form around the solute atoms, made up of a part contributed locally by the solute and a spatiallyvarying part associated with the highly susceptible palladium surrounding the solute atoms [4]. Ferromagnetism persists to small concentrations of solute, Dilute solutions of gadolinium and other rare earths in palladium are also ferromagnetic, but the giant moments are absent and for similar solute concentrations the Curie temperatures are much lower [5] There is controversy as to whether there is a net polarisation of the palladium matrix in these alloys, leading to a possible palladium contribution to the bulk magnetic moment. Originally, Crangle [5] found that in magnetic fields of around 2 T the overall magnetic moment in PdGd 8S alloys was less than that contributed by the Gd( 712) ion cores and concluded that the palladium solvent was polarised in the direction opposite to the gadolinium ion core magnetization. However, Guertin et of al. PdGd [6,7] alloys have and recently made extensive studies have found that in much stronger fields (up to 15 T) the moment reverts to the value normally associated .
with the Gd ion cores, with no apparent Pd contribution. These authors confirmed the lower magnetic moment in weaker fields. 1!he present measurements on mixed (Fe,Gd) salutes were undertaken with a view to trying to resolve this point. A master alloy Pd0 997Fe0 003 was selected as being that with the highest indicated moment per solute atom in the PdFe series. This was alloyed with respectively 0, 0.6, 2,4 and 6 atomic per cent of gadolinium, keeping the Pd: Fe ratio fixed. The alloys were made by arc melting the pure constituents under very clean conditions. There was very little weight loss during melting. Magnetizations were measured at many fixed temperatures between about 1.5 K and 15K in variable fields of up to 2 T, using a conventional force balance with independent control of field and field gradient [8] Curie temperatures 0 were estimated using the Arrott—Belov procedure [9, 10] Saturation magnetizations were found in two ways: (a) byTHT extrapolating graphs against the isothermal reciprocal of the of magnetization field H to where 1/H = 0, and then plotting the extrapolated values UT against the square of the temparature T. The saturation value is where .
.
Table 1 Magnetic data for (Pdo 997Fe0003) i_~Gd~ alloys, with x varying betweenOand 0.06. x
0
a00 ~vr~i
~ 0 0.006 0.02 0.04 0.06
9.5 5.9 5.5 5.5 6.5
moment
(a)
(b)
(c)
0.010 0.010 0.010 0.010 0.010
0.025 —0.002 —0.038 —0.085 —0.077
—I
kgi
1.82 2.62 5.9 10.9 18.3 1 = 1 emug1
=
0.035 — 0.050 0.042 0.113 0.14 0.210 0.28 0.358 0.42 1 erg Oe1 g1. Fields units: 1 T iO~Oe.
Magnetization units: 1 JT’kg
77
Volume 44A, number 2
the appropriate ‘‘lottie iron contribution in the
~ic
l’d(Sub Fe. IGd alloys. ractmg the sun o the tron and
8 5
‘I May 973
PI-IYSICS LETTERS
contributions Iront the nhscrved alloy moment and then tntrntahi ing it to I UI) per cent of palladiunt giveS cOlLitilti (c) in table - fhis value, the apparen I
-
4
I
I
I
gadol iniunt
I
non—local magnetic moment in ihie alloys. is plotted against the concentration ol gadolinium in lig. 1 (uric temperatures are also plotted. it seems that the eft~ctof adding Gd to a dilute PdFe alloy is to “poison’ the positive polarisation of the solute. That is. that the negative values in
—
2
c 2
I
I
-
colUmn (c) of table I correspond to polarisation itt the opposite direction. Such opposition between
-
-s
polarisations associated respectively with Gd and Fe
-
-
0
I
solutes would reflect in the exchange coupling hetween the local magnetic moments and would give rise to the rninimuni in Curie temperature that is oh-
I 0.02
0.04
0.06
Gd content x o ~Pd
997Fe003)~~d
tig. 1. (‘uric temperature (upper) and non-local inagnctk moments (lower) of (Pdo 997Fe0 OO3~i~Gd~alloys. -)
T—
.
=
.
.
0: and (b) by extrapolating the higher field
linear parts of the isotherrnal(au-r,H) graphs to where H = 0 and plotting these extrapolating values energy T against T— as before, obtaining finally u0 o The ‘ . two procedures gave identical values br the saturation magnetization at T 0. That is, u~ = 000. At the lowest temperatures the magnetization of each alloy appeared to be saturated over most of the field range used. The results are shown in table I Since the gadolinium atoms are in the stable 5 ., state there seems little doubt that their local ‘7 . . 4f magnetic moment is 7.0 ~B per atom. That ts. itt the alloys the Gd 4f electrons contribute magnetic moments as shown in column (a) of tab~eI. In the case of the ion solute the situation is not quite so clear. Low and Holden 4 used a neutron scatternig technique and found that for a series of five binary PdFe alloys containing between 0.26 and 4.0 atomic per cent of iron, the magnetic moment is 3d orbitals at the iron sites was (3.5 ±0.4) ~ It is assumed here that the moment locally associated with each iron atom is 3.5 p0. and column (b) in table I gives
78
served. To explain the results ot G Liertin er al 16. 71. that there is no apparent solvent polarization in bi.nary PdGd alloys in strong fields, it would be necessary to postulate that the applied field progressively uocouples the reversed solvent magnettzation. This would seem to be quite likely, since the magnetic . -. ~II-Iof a moment of 1 p in an applied I teld of . . 11 I ~ T is comparable with the energy kT for an niter. . . action temperature of 10K.
References Ill J. (rangtc. Phil. Mag. 5 (19613) 335. 121 J. C rangle and \\.R. Scott. J. Appi. Phys. 36 (196n) 92!.
131 R.M. l3ozorth Ct at., Phys. Rev. 122 (1961) I t57. 141 0G. Low and TM. tiolden. Proc. Phys. Soc. 89 (1966) 19. 51 J. Crangtc, Pliys. Rev. Len. 13(1964) 569. 161 R.P. Guertin Ct al.. .1. .Appt. Phys. 42 (1971)1550. 171 R ~. ~iertin ci at , [‘hys. Rev. 7B (1973) 274 181 W. Sucksmith and ii.. Thompson, Proc. Ro~..Soc (London) A255 (1954) 362.
[91 A. Arrott, Phys. Rev. 08 (1957) 1394. 1101 K.P. Belov and AN. Goryaga, lizika Metatl. 2 (1956) 3 -
PHYSICS LETTERS
21 May 1973
FERROMAGNETISM IN DILUTE TERNARY Pd(Fe, Gd) ALLOYS J. CRANGLE Department of Physics, University of Sheffield, Sheffield S3 7RH, UK Received 16 April 1973 In (Pdo
997Feooo3)1_~Gd~ alloys the apparent magnetic moment of the polarized palladium solvent falls sharply with increasing x, and changes sign. The Curie temperature goes through a broad minimum at x 0.02.
Ferromagnetism occurs in dilute solutions of iron or cobalt in palladium [1—3].Giant magnetic moments form around the solute atoms, made up of a part contributed locally by the solute and a spatiallyvarying part associated with the highly susceptible palladium surrounding the solute atoms [4]. Ferromagnetism persists to small concentrations of solute, Dilute solutions of gadolinium and other rare earths in palladium are also ferromagnetic, but the giant moments are absent and for similar solute concentrations the Curie temperatures are much lower [5] There is controversy as to whether there is a net polarisation of the palladium matrix in these alloys, leading to a possible palladium contribution to the bulk magnetic moment. Originally, Crangle [5] found that in magnetic fields of around 2 T the overall magnetic moment in PdGd 8S alloys was less than that contributed by the Gd( 712) ion cores and concluded that the palladium solvent was polarised in the direction opposite to the gadolinium ion core magnetization. However, Guertin et of al. PdGd [6,7] alloys have and recently made extensive studies have found that in much stronger fields (up to 15 T) the moment reverts to the value normally associated .
with the Gd ion cores, with no apparent Pd contribution. These authors confirmed the lower magnetic moment in weaker fields. 1!he present measurements on mixed (Fe,Gd) salutes were undertaken with a view to trying to resolve this point. A master alloy Pd0 997Fe0 003 was selected as being that with the highest indicated moment per solute atom in the PdFe series. This was alloyed with respectively 0, 0.6, 2,4 and 6 atomic per cent of gadolinium, keeping the Pd: Fe ratio fixed. The alloys were made by arc melting the pure constituents under very clean conditions. There was very little weight loss during melting. Magnetizations were measured at many fixed temperatures between about 1.5 K and 15K in variable fields of up to 2 T, using a conventional force balance with independent control of field and field gradient [8] Curie temperatures 0 were estimated using the Arrott—Belov procedure [9, 10] Saturation magnetizations were found in two ways: (a) byTHT extrapolating graphs against the isothermal reciprocal of the of magnetization field H to where 1/H = 0, and then plotting the extrapolated values UT against the square of the temparature T. The saturation value is where .
.
Table 1 Magnetic data for (Pdo 997Fe0003) i_~Gd~ alloys, with x varying betweenOand 0.06. x
0
a00 ~vr~i
~ 0 0.006 0.02 0.04 0.06
9.5 5.9 5.5 5.5 6.5
moment
(a)
(b)
(c)
0.010 0.010 0.010 0.010 0.010
0.025 —0.002 —0.038 —0.085 —0.077
—I
kgi
1.82 2.62 5.9 10.9 18.3 1 = 1 emug1
=
0.035 — 0.050 0.042 0.113 0.14 0.210 0.28 0.358 0.42 1 erg Oe1 g1. Fields units: 1 T iO~Oe.
Magnetization units: 1 JT’kg
77
Volume 44A, number 2
the appropriate ‘‘lottie iron contribution in the
~ic
l’d(Sub Fe. IGd alloys. ractmg the sun o the tron and
8 5
‘I May 973
PI-IYSICS LETTERS
contributions Iront the nhscrved alloy moment and then tntrntahi ing it to I UI) per cent of palladiunt giveS cOlLitilti (c) in table - fhis value, the apparen I
-
4
I
I
I
gadol iniunt
I
non—local magnetic moment in ihie alloys. is plotted against the concentration ol gadolinium in lig. 1 (uric temperatures are also plotted. it seems that the eft~ctof adding Gd to a dilute PdFe alloy is to “poison’ the positive polarisation of the solute. That is. that the negative values in
—
2
c 2
I
I
-
colUmn (c) of table I correspond to polarisation itt the opposite direction. Such opposition between
-
-s
polarisations associated respectively with Gd and Fe
-
-
0
I
solutes would reflect in the exchange coupling hetween the local magnetic moments and would give rise to the rninimuni in Curie temperature that is oh-
I 0.02
0.04
0.06
Gd content x o ~Pd
997Fe003)~~d
tig. 1. (‘uric temperature (upper) and non-local inagnctk moments (lower) of (Pdo 997Fe0 OO3~i~Gd~alloys. -)
T—
.
=
.
.
0: and (b) by extrapolating the higher field
linear parts of the isotherrnal(au-r,H) graphs to where H = 0 and plotting these extrapolating values energy T against T— as before, obtaining finally u0 o The ‘ . two procedures gave identical values br the saturation magnetization at T 0. That is, u~ = 000. At the lowest temperatures the magnetization of each alloy appeared to be saturated over most of the field range used. The results are shown in table I Since the gadolinium atoms are in the stable 5 ., state there seems little doubt that their local ‘7 . . 4f magnetic moment is 7.0 ~B per atom. That ts. itt the alloys the Gd 4f electrons contribute magnetic moments as shown in column (a) of tab~eI. In the case of the ion solute the situation is not quite so clear. Low and Holden 4 used a neutron scatternig technique and found that for a series of five binary PdFe alloys containing between 0.26 and 4.0 atomic per cent of iron, the magnetic moment is 3d orbitals at the iron sites was (3.5 ±0.4) ~ It is assumed here that the moment locally associated with each iron atom is 3.5 p0. and column (b) in table I gives
78
served. To explain the results ot G Liertin er al 16. 71. that there is no apparent solvent polarization in bi.nary PdGd alloys in strong fields, it would be necessary to postulate that the applied field progressively uocouples the reversed solvent magnettzation. This would seem to be quite likely, since the magnetic . -. ~II-Iof a moment of 1 p in an applied I teld of . . 11 I ~ T is comparable with the energy kT for an niter. . . action temperature of 10K.
References Ill J. (rangtc. Phil. Mag. 5 (19613) 335. 121 J. C rangle and \\.R. Scott. J. Appi. Phys. 36 (196n) 92!.
131 R.M. l3ozorth Ct at., Phys. Rev. 122 (1961) I t57. 141 0G. Low and TM. tiolden. Proc. Phys. Soc. 89 (1966) 19. 51 J. Crangtc, Pliys. Rev. Len. 13(1964) 569. 161 R.P. Guertin Ct al.. .1. .Appt. Phys. 42 (1971)1550. 171 R ~. ~iertin ci at , [‘hys. Rev. 7B (1973) 274 181 W. Sucksmith and ii.. Thompson, Proc. Ro~..Soc (London) A255 (1954) 362.
[91 A. Arrott, Phys. Rev. 08 (1957) 1394. 1101 K.P. Belov and AN. Goryaga, lizika Metatl. 2 (1956) 3 -