- Email: [email protected]
Ferromagnetic resonance in amorphous Co—P alloys
Journal of Magnetism and Magnetic Materials 9 (1978) 211-213 0 North-Holland Publishing Company
FERROMAGNETIC
RESONANCE IN AMORPHOUS Co-P ALLOYS
U. KULLMANN and G. DIETZ II. Physikalisches Institut der Universitiit zu K&I, Ztilpicher Str. 77, D-5000 K6ln 41, Fed. Rep. Germany
Received 7 April 1978
Ferromagnetic resonance of electrodeposited amorphous Co-P alloys was measured at room temperature. Annealing of the samples changes their resonance fields for both parallel and perpendicular orientation relative to the static magnetic field. This is interpreted as a change of the uniaxial magnetic anisotropy and the saturation polarisation of the sample which is caused by changes of structural short range order during thermal treatment.
1. Introduction
to the static magnetic field. Using Kittel’s formulas
161: Electrodeposited amorphous Co-P alloys have a magnetic anisotropy with an easy axis perpendicular to their surface [l-3]. As shown in [4,.5] it is important to discuss this anisotropy in connection with the structural short range order in amorphous materials since structural and magnetic properties are sensitively connected. Ferromagnetic resonance (FMR) is a method for measuring such anisotropy fields perpendicular to the surface directly. Changes in structural short range order should therefore give rise to changes of magnetic properties. These changes can be produced by thermal treatment of the samples.
one gets the gyromagnetic ratio y and the effective magnetic polarisation reff =I, - peHk. Here Hk is the uniaxial magnetic anisotropy field perpendicular to the surface of the sample, I, the saturation polarisation, and o the microwave frequency. HII and H1 are the measured resonance fields parallel and perpendicular to the sample. For the annealing experiments a special program was chosen: the sample was annealed for 22 h at temperatures between 353 K and 533 K in steps of 20 degrees. After each step it was cooled down to room temperature and FMR was measured.
2. Experimental Co-P alloys were electrodeposited on copper plates which were later chemically dissolved. We cut the sample for the FMR experiment out of the middle of the foils. The samples had a diameter of 3 mm and a thickness of 70 m. The phosphorus content was 21 at.% as determined by a wet chemical analysis. The amorphous state was checked by an X-ray experiment. For FMR measurements we used a microwave bridge. The Co-P foils were placed in the middle of a TErea-cavity. The microwave frequency was 9.6 GHz. The foils were orientated parallel and perpendicular
3. Results and discussion Fig. 1. shows the resonance fields measured at room temperature for both orientations of the sample after the aforementioned thermal treatments. For the as-prepared state from Kittel’s formulas one gets the spectroscopic splitting factor g = 2.12 and the effective polarisation Ieff = 0.558 T. To determine Hk we 211
U. Kullmann and G. Dietz /Ferromagnetic resonance in Co-Palloys
212
VQ-
Ieff
[Tl 1 l
_-
-.-.
/
I.‘.
q55-
\
\
L._,
\ ‘\ \ ‘\.
q50-
-T
0
300
Fig. 1. Resonance fields of an amorphous Co79Pz t alloy for parallel and perpendicular orientation of the foil relative to the static magnetic field, measured at room temperature after annealing for 22 hours at a temperature Ta.
Is = 0.567 T independently with a magnetometer after Neckenbtirger [7]. Using this value we obtained Hk = 7.96 X lo3 A/m. After each annealing step we calculated the spectroscopic splitting factor and the effective polarisation. In the amorphous state the g-factor is not changed by thermal treatment, as is shown in fig. 2. The mean value isg = 2.11 f 0.01. The effective polarisation shown in fig. 3 is much more affected. The increase after annealing at 373 K is attributed to the decrease of the uniaxial magnetic anisotropy [ 1,2]. We conclude that the preferential orientation in structural short range order built up
measured
v. 2,1.
I ----
. ..-
c-- ._.... ___ .*.. __.
2,P
3
o [“Cl
200
0 [“Cl
Fig. 3. Effective polarisation reff =I, - ,.QHk of an amorphous C079Pat calculated from Kittel’s formulas after annealing at r,.
-T 100
200
100
.
.
during preparation is destroyed more and more. There are two further characteristic temperatures at about 4 13 K and 493 K where Ieff decreases markedly This can be explained either by the building up of a uniaxial magnetic anisotropy or the decrease of the saturation polarisation. The first process has not been observed in other investigations up to now. A decrease ofZS, however, was also observed in two other independent experiments. The saturation polarisation calculated from hysteresis loops is shown in fig. 4. As can be seen the saturation polarisation decreases after annealing at 403 K and 493 K. Similar results we found from the measurement of 1, with the magnetometer mentioned above. The decrease at 493 K is attributed to crystallisation as can be seen by X-ray experiments. The decrease at 403 K, however, was not explained up to now.
0,79-
Is
IT1
I
<- a--c_;_ x 076 -
. --x-
-_*_
. _‘_
-_-I_-_ 4 I
q73 -T
o
Fig. 2. Spectroscopic splitting factor of an amorphous Co79P2 r alloy calculated from Kittel’s formulas after annealing at Ta.
AT OJO80
too
120
1Lo
160
a
18Oltl 200
220
Fig. 4. Saturation polarisation of an amorphous Co-P alloy obtained from hysteresis loops taken at room temperature after a thermal treatment for 22 h at a temperature Ta.
U. Kullmann and G. Dietz /Ferromagnetic resonance in Co-P alloys
213
4. Conclusions
Acknowledgements
Our experiments showed that there are three processes that change the FMR line position after annealing. The first two probably depend on changes in short range order while the third at 493 K is due to the crystallisation of the sample. The first manifests itself in a decrease of uniaxial magnetic anisotropy, the second in a decrease of saturation polarisation. What the change of the structural short range order looks like should be discussed with respect to changes of other structure sensitive properties of electrodeposited Co-P during thermal treatment [3-S], Besides, it should be checked to what extent the saturation polarisation is affected by the structural short range order. For this purpose more precise measurements of I, are necessary.
The authors wish to thank Th. Frechen for helpful discussions.
References
[l] G.S. Cargill III, R.J. Gambino and J.J. Cuomo, IEEE Trans. Magn. Mag. 10 (1974) 803. [ 21 G. Dietz and A. Hiinseler, J. Magn. Magn. Mat. 6 (1977) [3] EDietz and Th. Frechen, J. Magn. Magn. Mat. 6 (1977) 65. [4] G. Dietz, H. Bestgen and J. Hungenberg, this conference. [5] G. Dietz, J. Magn. Magn. Mat. 6 (1977) 47. [6] Ch. Kittel, Phys. Rev. 73 (1948) 155. [7] E. Neckenbiirger, Z. Angew. Physik 18 (1965) 440.
FERROMAGNETIC
RESONANCE IN AMORPHOUS Co-P ALLOYS
U. KULLMANN and G. DIETZ II. Physikalisches Institut der Universitiit zu K&I, Ztilpicher Str. 77, D-5000 K6ln 41, Fed. Rep. Germany
Received 7 April 1978
Ferromagnetic resonance of electrodeposited amorphous Co-P alloys was measured at room temperature. Annealing of the samples changes their resonance fields for both parallel and perpendicular orientation relative to the static magnetic field. This is interpreted as a change of the uniaxial magnetic anisotropy and the saturation polarisation of the sample which is caused by changes of structural short range order during thermal treatment.
1. Introduction
to the static magnetic field. Using Kittel’s formulas
161: Electrodeposited amorphous Co-P alloys have a magnetic anisotropy with an easy axis perpendicular to their surface [l-3]. As shown in [4,.5] it is important to discuss this anisotropy in connection with the structural short range order in amorphous materials since structural and magnetic properties are sensitively connected. Ferromagnetic resonance (FMR) is a method for measuring such anisotropy fields perpendicular to the surface directly. Changes in structural short range order should therefore give rise to changes of magnetic properties. These changes can be produced by thermal treatment of the samples.
one gets the gyromagnetic ratio y and the effective magnetic polarisation reff =I, - peHk. Here Hk is the uniaxial magnetic anisotropy field perpendicular to the surface of the sample, I, the saturation polarisation, and o the microwave frequency. HII and H1 are the measured resonance fields parallel and perpendicular to the sample. For the annealing experiments a special program was chosen: the sample was annealed for 22 h at temperatures between 353 K and 533 K in steps of 20 degrees. After each step it was cooled down to room temperature and FMR was measured.
2. Experimental Co-P alloys were electrodeposited on copper plates which were later chemically dissolved. We cut the sample for the FMR experiment out of the middle of the foils. The samples had a diameter of 3 mm and a thickness of 70 m. The phosphorus content was 21 at.% as determined by a wet chemical analysis. The amorphous state was checked by an X-ray experiment. For FMR measurements we used a microwave bridge. The Co-P foils were placed in the middle of a TErea-cavity. The microwave frequency was 9.6 GHz. The foils were orientated parallel and perpendicular
3. Results and discussion Fig. 1. shows the resonance fields measured at room temperature for both orientations of the sample after the aforementioned thermal treatments. For the as-prepared state from Kittel’s formulas one gets the spectroscopic splitting factor g = 2.12 and the effective polarisation Ieff = 0.558 T. To determine Hk we 211
U. Kullmann and G. Dietz /Ferromagnetic resonance in Co-Palloys
212
VQ-
Ieff
[Tl 1 l
_-
-.-.
/
I.‘.
q55-
\
\
L._,
\ ‘\ \ ‘\.
q50-
-T
0
300
Fig. 1. Resonance fields of an amorphous Co79Pz t alloy for parallel and perpendicular orientation of the foil relative to the static magnetic field, measured at room temperature after annealing for 22 hours at a temperature Ta.
Is = 0.567 T independently with a magnetometer after Neckenbtirger [7]. Using this value we obtained Hk = 7.96 X lo3 A/m. After each annealing step we calculated the spectroscopic splitting factor and the effective polarisation. In the amorphous state the g-factor is not changed by thermal treatment, as is shown in fig. 2. The mean value isg = 2.11 f 0.01. The effective polarisation shown in fig. 3 is much more affected. The increase after annealing at 373 K is attributed to the decrease of the uniaxial magnetic anisotropy [ 1,2]. We conclude that the preferential orientation in structural short range order built up
measured
v. 2,1.
I ----
. ..-
c-- ._.... ___ .*.. __.
2,P
3
o [“Cl
200
0 [“Cl
Fig. 3. Effective polarisation reff =I, - ,.QHk of an amorphous C079Pat calculated from Kittel’s formulas after annealing at r,.
-T 100
200
100
.
.
during preparation is destroyed more and more. There are two further characteristic temperatures at about 4 13 K and 493 K where Ieff decreases markedly This can be explained either by the building up of a uniaxial magnetic anisotropy or the decrease of the saturation polarisation. The first process has not been observed in other investigations up to now. A decrease ofZS, however, was also observed in two other independent experiments. The saturation polarisation calculated from hysteresis loops is shown in fig. 4. As can be seen the saturation polarisation decreases after annealing at 403 K and 493 K. Similar results we found from the measurement of 1, with the magnetometer mentioned above. The decrease at 493 K is attributed to crystallisation as can be seen by X-ray experiments. The decrease at 403 K, however, was not explained up to now.
0,79-
Is
IT1
I
<- a--c_;_ x 076 -
. --x-
-_*_
. _‘_
-_-I_-_ 4 I
q73 -T
o
Fig. 2. Spectroscopic splitting factor of an amorphous Co79P2 r alloy calculated from Kittel’s formulas after annealing at Ta.
AT OJO80
too
120
1Lo
160
a
18Oltl 200
220
Fig. 4. Saturation polarisation of an amorphous Co-P alloy obtained from hysteresis loops taken at room temperature after a thermal treatment for 22 h at a temperature Ta.
U. Kullmann and G. Dietz /Ferromagnetic resonance in Co-P alloys
213
4. Conclusions
Acknowledgements
Our experiments showed that there are three processes that change the FMR line position after annealing. The first two probably depend on changes in short range order while the third at 493 K is due to the crystallisation of the sample. The first manifests itself in a decrease of uniaxial magnetic anisotropy, the second in a decrease of saturation polarisation. What the change of the structural short range order looks like should be discussed with respect to changes of other structure sensitive properties of electrodeposited Co-P during thermal treatment [3-S], Besides, it should be checked to what extent the saturation polarisation is affected by the structural short range order. For this purpose more precise measurements of I, are necessary.
The authors wish to thank Th. Frechen for helpful discussions.
References
[l] G.S. Cargill III, R.J. Gambino and J.J. Cuomo, IEEE Trans. Magn. Mag. 10 (1974) 803. [ 21 G. Dietz and A. Hiinseler, J. Magn. Magn. Mat. 6 (1977) [3] EDietz and Th. Frechen, J. Magn. Magn. Mat. 6 (1977) 65. [4] G. Dietz, H. Bestgen and J. Hungenberg, this conference. [5] G. Dietz, J. Magn. Magn. Mat. 6 (1977) 47. [6] Ch. Kittel, Phys. Rev. 73 (1948) 155. [7] E. Neckenbiirger, Z. Angew. Physik 18 (1965) 440.