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Hydrogen induced changes in the magnetic properties of amorphous Fe-Zr alloys
Journal
of Magnetism
and Magnetic
Materials
HYDROGEN INDUCED Fe-Zr ALLOYS S.M. FRIES, Angewandte
CHANGES
U. GONSER,
Physik,
54-57
(1986) 287-288
287
IN THE MAGNETIC
PROPERTIES
OF AMORPHOUS
H.G. WAGNER
Universitiit des Saarlandes,
D -6600 Saarbriicken,
Fed. Rep. Germany
and C.L. CHIEN Department
of Physics, The Johns Hopkins University, Baltimore, Maryland 21218, USA
The changes in the magnetic properties of amorphous Fe-Zr alloys induced by hydrogenation have been studied by “Fe MBssbauer spectroscopy. Hydrogenation leads to an increase in the Curie temperature of the iron-rich alloys, whereas the zirconium-rich alloys are marked by their astonishingly large hydrogen uptake.
1. Introduction In many tion
of iron
3. Results and discussion
amorphous with
alloys,
a non-magnetic
formed metal,
by the combinaferromagnetism
occurs above a critical iron concentration x, = 40. For the amorphous Fe-Zr system the onset of magnetic ordering occurs above X, 2 45. The Curie temperature (Tc) is found to increase with x 2 45 and a clear maximum in T, is found at an Fe concentration of x = 85 [l]. Whereas the influence of hydrogenation on the magnetic properties of amorphous Fe_rZr,,_,Y melt-spun ribbons (88
2. Experimental Amorphous alloys of the nominal compositions Fe,,Zr,, and Fe,,Zr,, were prepared by conventional melt-spinning techniques. Amorphous Fe,Zr,,_, (20 .< x < 93) samples were produced using a high-rate sputtering technique [5] where the material was deposited on substrates of copper. The samples were electrolytically charged with hydrogen in a solution of glycerine and phosphoric acid, using constant current densities of 200 m&mm2 and charging times of two hours. A standard gas chromatograph was used to determine the quantity of absorbed hydrogen in the case of the melt-spun samples. The hydrogen content of the sputtered samples could not be exactly determined because of the uncertainties in the thicknesses of the copper substrates and the samples. The Mijssbauer spectra of the uncharged and charged amorphous Fe-Zr alloys were recorded at room temperature (RT) in conventional transmission geometry using a source of “Co in Rh. All isomer shifts are given relative to a-iron at RT.
0304-8853/86/$03.50
0 Elsevier Science Publishers
The magnetic ordering temperature (T,) of the Fe-Zr samples is shown in fig. 1 as a function of Fe concentration [l]. T, is found to be near or below room temperature for all compositions. Massbauer spectra of the amorphous Fe-Zr alloys taken at RT therefore show in each case a spectrum of paramagnetic alloys, in fact, an asymmetric broadened doublet which is due to a distribution of electric field gradients existing at the sites of the 57Fe nuclei. A satisfactory fit is obtained by introducing a linear correlation between the isomer shifts (IS) and the quadrupole splittings (QS): IS(QS) = aQS + b.
(1)
The distributions derived from this approach along with the resulting fits for four selected compositions are shown in fig. 2. There is a clear change in the asymmetry when going from Fe24Zr7, to Fe,,Zr,, and a general trend for the isomer shift to move from negative to more positive values. The data obtained from the distribution fitting procedure are summarized in table 1. Whereas the amorphous Fe-Zr alloys showed the normal flexible behaviour of amorphous metals, the
paramagnetic
Fig. 1. Magnetic ordering Fe,Zr,,_ j alloys [l].
B.V.
temperature
(T,)
of amorphous
SM. Fries
et al. /
Hyhgenutron
1 1
L
m
amorphous Fe- Zr allow
: 100 _ ;; z w 0.96
* .
1
..a
0
Velocity Fig. 2. Mlissbauer at RT.
!mm/s!
spectra
of amorphous
*. ‘t
.
05 1 OS [mm/s]
Fe,Zr,,,,
0.96
~, samples -2
-1
Velocity Fig. 3. Mbssbauer after hydrogenation
hydrogenated samples became embrittled by hydrogenation. There is a general trend towards increased hydrogen uptake with higher Zr content, going from a hydrogen to metal ratio of 0.5 for Fe,,Zr,, to 2.4 for Fe,,Zr,,. The influence of hydrogenation on the Mbssbauer spectra of amorphous Fe-Zr alloys is shown in fig. 3. The spectrum of Fe,,Zr,, clearly shows the magnetic phase transition enhanced by hydrogenation, increasing T<. from 254 K to approx. 400 K [2,4]. In the case of the alloy an unresolved magnetic hydrogenated Fe,,Zr,, hyperfine contribution is superimposed on the central component corresponding to an increase of 7c by about
Table 1 Parameters corresponds respectively
obtained by the distribution fitting procedure. QS to the mean quadrupole splitting and E to IS(QS)
Composition
a
h
QS(mm/s)
E (mm/s)
Fe,&r,,
+ 0.104
Fe,,Zr,, Fe,“Zr, Fc,,Zr,, Fe,“Zr, hydrogenated Fc,,Zr,, hydrogenated
+ 0.030 - 0.040 -0.116 + 0.050
-0.144 -0.157 -0.147 -0.192 +0.14
+0.360 +0.352 +0.347 i-O.550 + 0.49
- 0.107 ~0.146 -0.161 - 0.256 + 0.1645
+ 0.49
+ 0.335
2
spectra of amorphous at RT.
Fe,Zr,,,,
1 samples
PI KM. Unruh and C.L. Chien, Phys. Rev. B 30 (1984) 4968. PI Y. Boliang. D.H. Ryan. J.M.D. Coey, 2. Altounian. J. 0. StrGm-Olsen
to.31
1 [mm/s!
100 K. At RT the spectra of hydrogenated Fe,,,Zr,,, and Fe,,Fr,, differ from those of the uncharged samples bb a change in the asymmetry and more positive isomer shifts. Whereas for the charged Fe,,Zr,,, alloy the splitting increases at RT, the splitting of the hydrogenated Fe,,Zr,, samples decreases from QS = 0.55 to QS = 0.49 mm/s. The hydrogenated Fe,,Zr,, alloy shows no sign of magnetic order down to 1.5 K, the MGssbauer spectrum shows a constant quadrupole splitting with QS = 0.49 mm/s. There is a clear tendency for the T of amorphous Fe, Zr,,N _ , alloys to increase with hydrogenation for the iron-rich alloys, whereas the zirconium-rich alloys are marked by their change in IS by hydrogenation and their hydrogen uptake properties. Further investigations are underway for compositions between 40 G x < 60 at low temperatures to obtain information on a possible shift of x, and T for these alloys by hydrogenation.
and F. Razavi, J. Phys. F 13 (1983) 217. K. Nakanishi, H. Niroyoshi and N.S. Kazama. J. Appl. Phys. 53 (1982) 7792. [41 S.M. Fries. H.G. Wagner, U. Gonser, L. Schlapbach and R. Montiel-Montoya. J. Magn. Magn. Mat. 45 (1984) 331. [51C.L. Chien and K.M. Unruh, Phys. Rev. B 25 (1982) 5790.
PI H. Fujimori. + 0.052
0
of Magnetism
and Magnetic
Materials
HYDROGEN INDUCED Fe-Zr ALLOYS S.M. FRIES, Angewandte
CHANGES
U. GONSER,
Physik,
54-57
(1986) 287-288
287
IN THE MAGNETIC
PROPERTIES
OF AMORPHOUS
H.G. WAGNER
Universitiit des Saarlandes,
D -6600 Saarbriicken,
Fed. Rep. Germany
and C.L. CHIEN Department
of Physics, The Johns Hopkins University, Baltimore, Maryland 21218, USA
The changes in the magnetic properties of amorphous Fe-Zr alloys induced by hydrogenation have been studied by “Fe MBssbauer spectroscopy. Hydrogenation leads to an increase in the Curie temperature of the iron-rich alloys, whereas the zirconium-rich alloys are marked by their astonishingly large hydrogen uptake.
1. Introduction In many tion
of iron
3. Results and discussion
amorphous with
alloys,
a non-magnetic
formed metal,
by the combinaferromagnetism
occurs above a critical iron concentration x, = 40. For the amorphous Fe-Zr system the onset of magnetic ordering occurs above X, 2 45. The Curie temperature (Tc) is found to increase with x 2 45 and a clear maximum in T, is found at an Fe concentration of x = 85 [l]. Whereas the influence of hydrogenation on the magnetic properties of amorphous Fe_rZr,,_,Y melt-spun ribbons (88
2. Experimental Amorphous alloys of the nominal compositions Fe,,Zr,, and Fe,,Zr,, were prepared by conventional melt-spinning techniques. Amorphous Fe,Zr,,_, (20 .< x < 93) samples were produced using a high-rate sputtering technique [5] where the material was deposited on substrates of copper. The samples were electrolytically charged with hydrogen in a solution of glycerine and phosphoric acid, using constant current densities of 200 m&mm2 and charging times of two hours. A standard gas chromatograph was used to determine the quantity of absorbed hydrogen in the case of the melt-spun samples. The hydrogen content of the sputtered samples could not be exactly determined because of the uncertainties in the thicknesses of the copper substrates and the samples. The Mijssbauer spectra of the uncharged and charged amorphous Fe-Zr alloys were recorded at room temperature (RT) in conventional transmission geometry using a source of “Co in Rh. All isomer shifts are given relative to a-iron at RT.
0304-8853/86/$03.50
0 Elsevier Science Publishers
The magnetic ordering temperature (T,) of the Fe-Zr samples is shown in fig. 1 as a function of Fe concentration [l]. T, is found to be near or below room temperature for all compositions. Massbauer spectra of the amorphous Fe-Zr alloys taken at RT therefore show in each case a spectrum of paramagnetic alloys, in fact, an asymmetric broadened doublet which is due to a distribution of electric field gradients existing at the sites of the 57Fe nuclei. A satisfactory fit is obtained by introducing a linear correlation between the isomer shifts (IS) and the quadrupole splittings (QS): IS(QS) = aQS + b.
(1)
The distributions derived from this approach along with the resulting fits for four selected compositions are shown in fig. 2. There is a clear change in the asymmetry when going from Fe24Zr7, to Fe,,Zr,, and a general trend for the isomer shift to move from negative to more positive values. The data obtained from the distribution fitting procedure are summarized in table 1. Whereas the amorphous Fe-Zr alloys showed the normal flexible behaviour of amorphous metals, the
paramagnetic
Fig. 1. Magnetic ordering Fe,Zr,,_ j alloys [l].
B.V.
temperature
(T,)
of amorphous
SM. Fries
et al. /
Hyhgenutron
1 1
L
m
amorphous Fe- Zr allow
: 100 _ ;; z w 0.96
* .
1
..a
0
Velocity Fig. 2. Mlissbauer at RT.
!mm/s!
spectra
of amorphous
*. ‘t
.
05 1 OS [mm/s]
Fe,Zr,,,,
0.96
~, samples -2
-1
Velocity Fig. 3. Mbssbauer after hydrogenation
hydrogenated samples became embrittled by hydrogenation. There is a general trend towards increased hydrogen uptake with higher Zr content, going from a hydrogen to metal ratio of 0.5 for Fe,,Zr,, to 2.4 for Fe,,Zr,,. The influence of hydrogenation on the Mbssbauer spectra of amorphous Fe-Zr alloys is shown in fig. 3. The spectrum of Fe,,Zr,, clearly shows the magnetic phase transition enhanced by hydrogenation, increasing T<. from 254 K to approx. 400 K [2,4]. In the case of the alloy an unresolved magnetic hydrogenated Fe,,Zr,, hyperfine contribution is superimposed on the central component corresponding to an increase of 7c by about
Table 1 Parameters corresponds respectively
obtained by the distribution fitting procedure. QS to the mean quadrupole splitting and E to IS(QS)
Composition
a
h
QS(mm/s)
E (mm/s)
Fe,&r,,
+ 0.104
Fe,,Zr,, Fe,“Zr, Fc,,Zr,, Fe,“Zr, hydrogenated Fc,,Zr,, hydrogenated
+ 0.030 - 0.040 -0.116 + 0.050
-0.144 -0.157 -0.147 -0.192 +0.14
+0.360 +0.352 +0.347 i-O.550 + 0.49
- 0.107 ~0.146 -0.161 - 0.256 + 0.1645
+ 0.49
+ 0.335
2
spectra of amorphous at RT.
Fe,Zr,,,,
1 samples
PI KM. Unruh and C.L. Chien, Phys. Rev. B 30 (1984) 4968. PI Y. Boliang. D.H. Ryan. J.M.D. Coey, 2. Altounian. J. 0. StrGm-Olsen
to.31
1 [mm/s!
100 K. At RT the spectra of hydrogenated Fe,,,Zr,,, and Fe,,Fr,, differ from those of the uncharged samples bb a change in the asymmetry and more positive isomer shifts. Whereas for the charged Fe,,Zr,,, alloy the splitting increases at RT, the splitting of the hydrogenated Fe,,Zr,, samples decreases from QS = 0.55 to QS = 0.49 mm/s. The hydrogenated Fe,,Zr,, alloy shows no sign of magnetic order down to 1.5 K, the MGssbauer spectrum shows a constant quadrupole splitting with QS = 0.49 mm/s. There is a clear tendency for the T of amorphous Fe, Zr,,N _ , alloys to increase with hydrogenation for the iron-rich alloys, whereas the zirconium-rich alloys are marked by their change in IS by hydrogenation and their hydrogen uptake properties. Further investigations are underway for compositions between 40 G x < 60 at low temperatures to obtain information on a possible shift of x, and T for these alloys by hydrogenation.
and F. Razavi, J. Phys. F 13 (1983) 217. K. Nakanishi, H. Niroyoshi and N.S. Kazama. J. Appl. Phys. 53 (1982) 7792. [41 S.M. Fries. H.G. Wagner, U. Gonser, L. Schlapbach and R. Montiel-Montoya. J. Magn. Magn. Mat. 45 (1984) 331. [51C.L. Chien and K.M. Unruh, Phys. Rev. B 25 (1982) 5790.
PI H. Fujimori. + 0.052
0