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Magnetometrical study of cobalt doped YIG garnet films
Journal of Magnetism and Magnetic Materials 83 (1990) 87-88 North-Holland
MAGNETOMETRICAL A. MAZIEWSKI, Institute
of Physics,
87
STUDY OF COBALT
L. PfiST
’ and P. GGRNERT
Warsaw University Branch, Biabstok,
DOPED YIG GARNET FILMS * *
Poland
Peculiar magnetization processes (e.g. shift of hysteresis loops) were observed at room temperature in (YCa),(FeCoGe),O,, films. Vibrating samples magnetometer temperature. The idea of energetically peculiarities.
was used for the sample study. No compensation point was found around room inequivalent easy magnetization axes seems to be useful for the explanation of the
1. Introduction
2. Experimental
Anomalous magnetization processes have been observed [l] using the Faraday effect in (YCa), films grown on (100) plane of GGG (FeCoGe),O,, substrate (more information about sample preparation is given in ref. [2]). Four types of domain structure (DS), called P,. P,, P, or P,, phase, were reported [l]. DS in the phase has been characterized by different amplitude of “up” and “down” directed field necessary for DS vanishing. Magnetization processes in these samples were investigated (qualitative analysis of three magnetization components changes) by low frequency susceptibility technique based on flux changes measurement [3]. In the phase an asymmetry of the hysteresis loop M, (H,) has been found (without real changes of magnetization M,,). The I or ]I marks defined a component perpendicular or parallel to a sample plane, respectively. Magnetic field induced changes between phases have been connected with changes of as well M, as M,, component. The asymmetry of hysteresis loops could be flipped (by switch between phases) by a low (= 50 Oe) external magnetic field. Similar effects have been observed in other magnetic materials e.g. in exchange coupled soft and hard magnetic material system [4] (our samples are characterized by much lower switching field). Peculiar magneto-optical and magnetic hysteresis has been observed also near the compensation temperature on some garnet materials [5,6]. In spite of the effort [1,3] the magnetic structure and related magnetization processes are not fully understood. The extensive study of magnetization processes was done using vibrating sample magnetometer (VSM) to understand the effects observed in our material.
The temperature dependence of magnetization was measured by VSM in the temperature range 20-500 K, see fig. 1. There is no compensation point nor other peculiarities around the room temperature and the magnetization compensation idea cannot explain the anomalous magnetization processes. The negative first cubic anisotropy constant K, (K, amplitude larger than amplitudes of uniaxial and orthorhombic anisotropy constants) was found [7] in our samples. Two quite different types of DS can be constructed (see fig. 2) with different sample M,, magneti-
* The work was partially supported by the subject no. CPBP 01.04. ’ Institute of Physics, CSAV, Prague, Czechoslovakia. ’ Physikalisch-Technisches Institut, Jena, German Dem. Rep. 0304-8853/90/$03.50 (North-Holland)
0 Elsevier Science Publishers
B.V.
1 “@
00
60.0
0
60
0
40
0
13
3
G
Tl!i, 3
Fig.
1. Temperature dependence (YCa),(FeCoGe),O,,
of
the magnetization film.
in
Fig. 2. Easy directions ED, of magnetization defined for a magnet characterised by cubic magnetic anisotropy with negative K, constant.
A.
Mazmvski
et al.
/ Cobalt
-ICOel
doped
YfG
garnet
fibs
zation in plane component calculated for remanent DS with both domains having equal volumes: (i) magnetization along ED, and ED, (M,, = 0); (ii) magnetization along ED, and ED, (M,, = O.&V,). M, is the saturation magnetization value. The second DS type was preferred by the experiments, see fig. 3a where the P, and P, phases can be obtained using a domain with magnetization along ED,, ED, and ED,, ED,, respectively. The magnetization component along applied external field M( H( $I)) was measured at room temperature for a different field orientation. # is the angle between the field and the normal to the sample plane. Hysteresis curves are different (see fig. 3b) changing the $I sign. A different anisotropy energy could be expected for magnetization oriented along [ill] and [ll]] direction. Anisotropy term K,(M* n,) can produce the difference. The n, vector defines the easy axis (or the normal to the easy plane) direction inclined from sample normal. The [OOl] axis deviation from the sample normal is responsible for the inclination. The magnetization processes (curves obtained for C/I= 0 o and - 30’ in fig. 3b) undergo with combined domain wall motion and changes between phases. P, -+ P, or P, + P, transitions occur in a higher field than domain wall motion for curve obtained for $I = 30” (see fig. 3b). The loops from fig. 3c were taken for the sample in a homogenous phase state - only the domain wall motion during the magnetization process. The P, or P, phases have been obtained after the film saturation applying magnetic field ( I$ = 90 o ) equal to + 100 or - 100 Oe, respectively. Asymmetry of the hysteresis loops from fig. 3c can be explained using the inequivalent easy axes idea. Some problems connected with asymmetric domain structures (characterized by inequivalent easy axis) were discussed in ref. [8]. References
(11A.
Maziewski,
IEEE
PI
Trans.
P. Gornert,
M. Kisielewski,
P. Gornert
Magn. MAG-23 M. Neviiva,
(1987)
and K. Brzosko,
3367.
J. SimSova, W. Andra,
P. SumSal and B. Bubakovb.
W. Schtippel,
Phys. Stat. Sol. (a) 74 (1982)
107. I31 M. Kisielewski, A. Maziewski Conf. on Physics of Magnetic land, 1988,
Acta
and P. Giirnert, Materials,
Phys. Polon.
(1989)
[51 M. Rosenberg, Magn. Magn. Fig. 3. The M, ( = M( H)/M,)
different field inclination $ 90°; (c)
hysteresis
(b) cp=O (full line), +=+30“(*) 4’ = - 10,
sample
P,
saturation
and
P,
loops obtained for a
from the sample phases
have
(a) I#J=
produced
-100
[61 H.R.
Miiller.
Schmidt
after
Oe, respec-
Slovaca
(1989)
PI A. Maziewski,
Appl. Phys.
296. R. Vernhard,
C. Borghese
Mat. 7 (1978) B. Knappe.
and A. Funke,
I71 A. Maziewski,
and 4=-30“(+); been
using a field of 100 and tively.
normal.
Po-
in press.
[41 F. Hellman, R.B. van Dover and E.M. Gyorgy, Lett. 50 (1987)
4th Intern.
Szczyrk-Bila,
and R. Tappa.
J.
44. R.
Kosicik,
P. Rosemann,
Phys. Stat. Sol. (a) 36 (1976)
B. Szymahski
D. 617.
and P. Gijrnert,
Acta
Phys.
L. Murtinova,
Acta
Phys.
in press. Z.
Polon. A72 (1987)
Babicz 811.
and
MAGNETOMETRICAL A. MAZIEWSKI, Institute
of Physics,
87
STUDY OF COBALT
L. PfiST
’ and P. GGRNERT
Warsaw University Branch, Biabstok,
DOPED YIG GARNET FILMS * *
Poland
Peculiar magnetization processes (e.g. shift of hysteresis loops) were observed at room temperature in (YCa),(FeCoGe),O,, films. Vibrating samples magnetometer temperature. The idea of energetically peculiarities.
was used for the sample study. No compensation point was found around room inequivalent easy magnetization axes seems to be useful for the explanation of the
1. Introduction
2. Experimental
Anomalous magnetization processes have been observed [l] using the Faraday effect in (YCa), films grown on (100) plane of GGG (FeCoGe),O,, substrate (more information about sample preparation is given in ref. [2]). Four types of domain structure (DS), called P,. P,, P, or P,, phase, were reported [l]. DS in the phase has been characterized by different amplitude of “up” and “down” directed field necessary for DS vanishing. Magnetization processes in these samples were investigated (qualitative analysis of three magnetization components changes) by low frequency susceptibility technique based on flux changes measurement [3]. In the phase an asymmetry of the hysteresis loop M, (H,) has been found (without real changes of magnetization M,,). The I or ]I marks defined a component perpendicular or parallel to a sample plane, respectively. Magnetic field induced changes between phases have been connected with changes of as well M, as M,, component. The asymmetry of hysteresis loops could be flipped (by switch between phases) by a low (= 50 Oe) external magnetic field. Similar effects have been observed in other magnetic materials e.g. in exchange coupled soft and hard magnetic material system [4] (our samples are characterized by much lower switching field). Peculiar magneto-optical and magnetic hysteresis has been observed also near the compensation temperature on some garnet materials [5,6]. In spite of the effort [1,3] the magnetic structure and related magnetization processes are not fully understood. The extensive study of magnetization processes was done using vibrating sample magnetometer (VSM) to understand the effects observed in our material.
The temperature dependence of magnetization was measured by VSM in the temperature range 20-500 K, see fig. 1. There is no compensation point nor other peculiarities around the room temperature and the magnetization compensation idea cannot explain the anomalous magnetization processes. The negative first cubic anisotropy constant K, (K, amplitude larger than amplitudes of uniaxial and orthorhombic anisotropy constants) was found [7] in our samples. Two quite different types of DS can be constructed (see fig. 2) with different sample M,, magneti-
* The work was partially supported by the subject no. CPBP 01.04. ’ Institute of Physics, CSAV, Prague, Czechoslovakia. ’ Physikalisch-Technisches Institut, Jena, German Dem. Rep. 0304-8853/90/$03.50 (North-Holland)
0 Elsevier Science Publishers
B.V.
1 “@
00
60.0
0
60
0
40
0
13
3
G
Tl!i, 3
Fig.
1. Temperature dependence (YCa),(FeCoGe),O,,
of
the magnetization film.
in
Fig. 2. Easy directions ED, of magnetization defined for a magnet characterised by cubic magnetic anisotropy with negative K, constant.
A.
Mazmvski
et al.
/ Cobalt
-ICOel
doped
YfG
garnet
fibs
zation in plane component calculated for remanent DS with both domains having equal volumes: (i) magnetization along ED, and ED, (M,, = 0); (ii) magnetization along ED, and ED, (M,, = O.&V,). M, is the saturation magnetization value. The second DS type was preferred by the experiments, see fig. 3a where the P, and P, phases can be obtained using a domain with magnetization along ED,, ED, and ED,, ED,, respectively. The magnetization component along applied external field M( H( $I)) was measured at room temperature for a different field orientation. # is the angle between the field and the normal to the sample plane. Hysteresis curves are different (see fig. 3b) changing the $I sign. A different anisotropy energy could be expected for magnetization oriented along [ill] and [ll]] direction. Anisotropy term K,(M* n,) can produce the difference. The n, vector defines the easy axis (or the normal to the easy plane) direction inclined from sample normal. The [OOl] axis deviation from the sample normal is responsible for the inclination. The magnetization processes (curves obtained for C/I= 0 o and - 30’ in fig. 3b) undergo with combined domain wall motion and changes between phases. P, -+ P, or P, + P, transitions occur in a higher field than domain wall motion for curve obtained for $I = 30” (see fig. 3b). The loops from fig. 3c were taken for the sample in a homogenous phase state - only the domain wall motion during the magnetization process. The P, or P, phases have been obtained after the film saturation applying magnetic field ( I$ = 90 o ) equal to + 100 or - 100 Oe, respectively. Asymmetry of the hysteresis loops from fig. 3c can be explained using the inequivalent easy axes idea. Some problems connected with asymmetric domain structures (characterized by inequivalent easy axis) were discussed in ref. [8]. References
(11A.
Maziewski,
IEEE
PI
Trans.
P. Gornert,
M. Kisielewski,
P. Gornert
Magn. MAG-23 M. Neviiva,
(1987)
and K. Brzosko,
3367.
J. SimSova, W. Andra,
P. SumSal and B. Bubakovb.
W. Schtippel,
Phys. Stat. Sol. (a) 74 (1982)
107. I31 M. Kisielewski, A. Maziewski Conf. on Physics of Magnetic land, 1988,
Acta
and P. Giirnert, Materials,
Phys. Polon.
(1989)
[51 M. Rosenberg, Magn. Magn. Fig. 3. The M, ( = M( H)/M,)
different field inclination $ 90°; (c)
hysteresis
(b) cp=O (full line), +=+30“(*) 4’ = - 10,
sample
P,
saturation
and
P,
loops obtained for a
from the sample phases
have
(a) I#J=
produced
-100
[61 H.R.
Miiller.
Schmidt
after
Oe, respec-
Slovaca
(1989)
PI A. Maziewski,
Appl. Phys.
296. R. Vernhard,
C. Borghese
Mat. 7 (1978) B. Knappe.
and A. Funke,
I71 A. Maziewski,
and 4=-30“(+); been
using a field of 100 and tively.
normal.
Po-
in press.
[41 F. Hellman, R.B. van Dover and E.M. Gyorgy, Lett. 50 (1987)
4th Intern.
Szczyrk-Bila,
and R. Tappa.
J.
44. R.
Kosicik,
P. Rosemann,
Phys. Stat. Sol. (a) 36 (1976)
B. Szymahski
D. 617.
and P. Gijrnert,
Acta
Phys.
L. Murtinova,
Acta
Phys.
in press. Z.
Polon. A72 (1987)
Babicz 811.
and