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Pulse high magnetic field magnetoresistance measurements in In3Sn alloys
Journal of Magnetism and Magnetic Materials 11 (1979) 233-235 © North-Holland Publishing Company
PULSE HIGH MAGNETIC FIELD MAGNETORESISTANCE MEASUREMENTS IN In3Sn ALLOYS
M. SURMA Institute of Physics, A. Mickiewicz University, Grunwaldzka 6, 60- 780 Poznah, Poland Received 28 July 1978
Pulsed high magnetic fields and a single-pulse rectangular shaped current are applied for magnetoresistance measurements of In3Sn alloys, at 77 K. The applied magnetic field strength exceeded 100 kG and the anisotropy of the sample magnetoresistance was investigated in the (a, c) crystallographiealplane. For many directions o f / / i n the (a, c) plane, negative magnetoresistance was observed.
Magnetoresistance measurements in InsSn alloys were carrierd out for samples o f 14%, 18% 25%, 30% and 33% atomic concentration of tin in the alloy. The temperature o f the sample was 77 K, and a current o f 5 A was switched through the sample. The sample conducted a single-pulse rectangular-shaped current o f 5 A (fig. lc) during a period o f 1.5 ms whereas the
magnetic field pulse o f the shape shown in fig. l a acted during 0.45 ms. Measurements were carried in two basic ways: (1) the sample current was switched on before applying the magnetic field pulse and was switched off when the magnetic field pulse, acting on the sample, had passed its maximum (fig. I a and c); (2) switching on of the sample current and magnetic field pulse were synchronized and the sample current was constant during the magnetic field pulse (fig. 2a and b). The peak value o f the magnetic field strength appeared roughly within 0.2 ms after switching on.
H(t) [a)
t
I (b) (c) . ~
Fig. 2. (a) Oscillograms: A - effect of the compensation of the induced voltages Uil, Ui2; B - magnetic field pulse H(t); C - rectangular-shaped current pulse; Hma x = 140 kG. (b) OsciUograms: A - signal of the voltage: Us = Up(H) + Ui; B - signal of the voltage: U0s = Ui; C - signal of the voltage Up(H= 0);Hma x = 140 kG; Ui = Uil - Ui2.
Fig. 1. Magnetic field pulse (a), magnetoresistance effect (b) and voltage pulse Up(H = O) (c). 233
M. Surma/ Magnetoresistance measurements in InsSn alloys
234
0
Uil
Sample1 t RI~10-2',q _r---k
+~
US R:10kA [~ Sampl2e
0
Fig. 3. Compensation circuit of the induced voltage Oil and
Ui2.
Magnetoresistance studies were realized by scope recording of the voltage across the sample. The samples RRR value was of the order of 2 up to 8. Measurements of the magnetoresistance in metals and metallic alloys by pulsed magnetic field of high strength technique are very difficult because, during the magnetic field pulse, induced voltage effects dq~[dt in the sample and in the sample current loop, as well as in the magnetoresistance voltage loop, affect the output signal. As a result of the induced voltage effects, the output signal is of the order of several volts, whereas the magnetoresistance voltage across the sample is of the order of several millivolts. The induction effects on the sample, on the sample current loop and magnetoresistance voltage electrodes loop generate a spurious voltage signal. This signal has to be rejected or minimized to the value of millivolts. For this purpose the compensation circuit shown in fig. 3 was used. The compensation circuit consisted sample 1 and sample 2 of similar geometrical shape, equal resistance and equal electrode loops. The sample resistance was of the order 10 - 3 - 1 0 -4 ~2. Sample 1 and sample 2 were placed inside the coil producing the magnetic field of high strength, During the field pulse the rectangular-shaped current was conducting only through sample 1. Across sample 1, the magnetoresistance voltage Up was present as well as the voltage Uil. The source of the latter resided in the induction effects. At the same field pulse, on the output of sample 2 there appeared the induction voltage Ui2 only. The voltage signals Uil + Up and - U i 2 added up resulting in the Us = Uil + Up - Ui2 voltage recorded by scope. If it is possible to achieve Uil = Ui2, the recorded voltage Us = Up and Us represents the pure
magnetoresistance signal. Figs. lb 2a and 2b show a good result of spurious voltage compensation by this method. The graph of the output signal recorded in fig. lb shows that the compensation of the spurious voltages was perfect: Uil - Ui2 = 0 and Us = Up(H), where Up(H) = IpR (H). The R (H) value represents magnetoresistance of the sample at magnetic field H and Ip denotes the current intensity conducted through the sample. The resulting value of [Up(H) - Up(H = 0)] = Ip[R(H) - R(0)] can be measured from the osciUograms presented in fig. lb and c. Thus, the quantity AR/R (0) = [R (H) - R (0)] [ R(0) defining the sample magnetoresistance is known. Here, R (13) denotes the sample resistance. For some samples the induced voltage (Uit - Ui2) was not reduced to zero, as can be seen in figs. 2a and b, because of different geometry of the samples loops. In this case two oscillograms had to be recorded (fig. 2b): ( I ) the trace (A) is recorded and represents the voltage Us = Up(/-/) + Uil - Ui2; (2) the trace (B) is recorded and represents only the result of the induced voltage Uos = Uil - Ui2 because no current Ip was conducted either through sample 1 or sample 2 in the compensation circuit. By subtracting the signals Us and Uos (traces A and B in fig. 2 b ) t h e magnetoresistance of the sample was measured as Us - Uos -- Up(H) and the voltage Up(H - 0) was known from the trace (C) given by the signal IpR(0). The two basic experimental methods mentioned above were used in the magnetoresistance measurements. Table 1 shows results of the AR/R(O) ratio for
Table 1 Magnetoresistance of In3Sn Alloys in magnetic field intensity of 120 kG, at temperature of 77 K ~(B, c)
Atomic concentration of Sn 14%
25%
30%
33%
0°
-
-0.5
-0.5
-0.3
20° 30° 40 ° 50° 60 ° 70° 80° 90°
-0.2 0 -0.3 -0.3 -0.5 0.2
-0.5 -0.3 -0.2 -0.2 0 0.2 0.7
-0.9 -1 -0.5 -
0 0 0 -0.6 -0.3
M. Surma /Magnetoresistance measurements in In3Sn alloys
the investigated In3Sn alloys. These results concern the transversal magnetoresistance anisotropy at the (a, c) plane of the InaSn monocrystals, at a magneti~ field strength of 120 kG. For many directions of H with respect to the c-axis of the crystals, negative magnetoresistance was observed. The highest value of negative magnetoresistance (AR/R(O) = - 1 ) was measured for the alloy of 30% atomic tin concentration and for H oriented at 60 ° with respect to the c-axis of the monocrystal. There is no evidence of negative magnetoresistance
235
when applying low magnetic fields. We believe that the negative magnetoresistance behaviour in InaSn alloys can be explained theoreticaUy on the results [1] for the third-band electronic structure of the InaSn alloys.
References [ 1] S. Maciejewskiand M. Surma, Acta Phys. Polon. A51 (1977) 265.
PULSE HIGH MAGNETIC FIELD MAGNETORESISTANCE MEASUREMENTS IN In3Sn ALLOYS
M. SURMA Institute of Physics, A. Mickiewicz University, Grunwaldzka 6, 60- 780 Poznah, Poland Received 28 July 1978
Pulsed high magnetic fields and a single-pulse rectangular shaped current are applied for magnetoresistance measurements of In3Sn alloys, at 77 K. The applied magnetic field strength exceeded 100 kG and the anisotropy of the sample magnetoresistance was investigated in the (a, c) crystallographiealplane. For many directions o f / / i n the (a, c) plane, negative magnetoresistance was observed.
Magnetoresistance measurements in InsSn alloys were carrierd out for samples o f 14%, 18% 25%, 30% and 33% atomic concentration of tin in the alloy. The temperature o f the sample was 77 K, and a current o f 5 A was switched through the sample. The sample conducted a single-pulse rectangular-shaped current o f 5 A (fig. lc) during a period o f 1.5 ms whereas the
magnetic field pulse o f the shape shown in fig. l a acted during 0.45 ms. Measurements were carried in two basic ways: (1) the sample current was switched on before applying the magnetic field pulse and was switched off when the magnetic field pulse, acting on the sample, had passed its maximum (fig. I a and c); (2) switching on of the sample current and magnetic field pulse were synchronized and the sample current was constant during the magnetic field pulse (fig. 2a and b). The peak value o f the magnetic field strength appeared roughly within 0.2 ms after switching on.
H(t) [a)
t
I (b) (c) . ~
Fig. 2. (a) Oscillograms: A - effect of the compensation of the induced voltages Uil, Ui2; B - magnetic field pulse H(t); C - rectangular-shaped current pulse; Hma x = 140 kG. (b) OsciUograms: A - signal of the voltage: Us = Up(H) + Ui; B - signal of the voltage: U0s = Ui; C - signal of the voltage Up(H= 0);Hma x = 140 kG; Ui = Uil - Ui2.
Fig. 1. Magnetic field pulse (a), magnetoresistance effect (b) and voltage pulse Up(H = O) (c). 233
M. Surma/ Magnetoresistance measurements in InsSn alloys
234
0
Uil
Sample1 t RI~10-2',q _r---k
+~
US R:10kA [~ Sampl2e
0
Fig. 3. Compensation circuit of the induced voltage Oil and
Ui2.
Magnetoresistance studies were realized by scope recording of the voltage across the sample. The samples RRR value was of the order of 2 up to 8. Measurements of the magnetoresistance in metals and metallic alloys by pulsed magnetic field of high strength technique are very difficult because, during the magnetic field pulse, induced voltage effects dq~[dt in the sample and in the sample current loop, as well as in the magnetoresistance voltage loop, affect the output signal. As a result of the induced voltage effects, the output signal is of the order of several volts, whereas the magnetoresistance voltage across the sample is of the order of several millivolts. The induction effects on the sample, on the sample current loop and magnetoresistance voltage electrodes loop generate a spurious voltage signal. This signal has to be rejected or minimized to the value of millivolts. For this purpose the compensation circuit shown in fig. 3 was used. The compensation circuit consisted sample 1 and sample 2 of similar geometrical shape, equal resistance and equal electrode loops. The sample resistance was of the order 10 - 3 - 1 0 -4 ~2. Sample 1 and sample 2 were placed inside the coil producing the magnetic field of high strength, During the field pulse the rectangular-shaped current was conducting only through sample 1. Across sample 1, the magnetoresistance voltage Up was present as well as the voltage Uil. The source of the latter resided in the induction effects. At the same field pulse, on the output of sample 2 there appeared the induction voltage Ui2 only. The voltage signals Uil + Up and - U i 2 added up resulting in the Us = Uil + Up - Ui2 voltage recorded by scope. If it is possible to achieve Uil = Ui2, the recorded voltage Us = Up and Us represents the pure
magnetoresistance signal. Figs. lb 2a and 2b show a good result of spurious voltage compensation by this method. The graph of the output signal recorded in fig. lb shows that the compensation of the spurious voltages was perfect: Uil - Ui2 = 0 and Us = Up(H), where Up(H) = IpR (H). The R (H) value represents magnetoresistance of the sample at magnetic field H and Ip denotes the current intensity conducted through the sample. The resulting value of [Up(H) - Up(H = 0)] = Ip[R(H) - R(0)] can be measured from the osciUograms presented in fig. lb and c. Thus, the quantity AR/R (0) = [R (H) - R (0)] [ R(0) defining the sample magnetoresistance is known. Here, R (13) denotes the sample resistance. For some samples the induced voltage (Uit - Ui2) was not reduced to zero, as can be seen in figs. 2a and b, because of different geometry of the samples loops. In this case two oscillograms had to be recorded (fig. 2b): ( I ) the trace (A) is recorded and represents the voltage Us = Up(/-/) + Uil - Ui2; (2) the trace (B) is recorded and represents only the result of the induced voltage Uos = Uil - Ui2 because no current Ip was conducted either through sample 1 or sample 2 in the compensation circuit. By subtracting the signals Us and Uos (traces A and B in fig. 2 b ) t h e magnetoresistance of the sample was measured as Us - Uos -- Up(H) and the voltage Up(H - 0) was known from the trace (C) given by the signal IpR(0). The two basic experimental methods mentioned above were used in the magnetoresistance measurements. Table 1 shows results of the AR/R(O) ratio for
Table 1 Magnetoresistance of In3Sn Alloys in magnetic field intensity of 120 kG, at temperature of 77 K ~(B, c)
Atomic concentration of Sn 14%
25%
30%
33%
0°
-
-0.5
-0.5
-0.3
20° 30° 40 ° 50° 60 ° 70° 80° 90°
-0.2 0 -0.3 -0.3 -0.5 0.2
-0.5 -0.3 -0.2 -0.2 0 0.2 0.7
-0.9 -1 -0.5 -
0 0 0 -0.6 -0.3
M. Surma /Magnetoresistance measurements in In3Sn alloys
the investigated In3Sn alloys. These results concern the transversal magnetoresistance anisotropy at the (a, c) plane of the InaSn monocrystals, at a magneti~ field strength of 120 kG. For many directions of H with respect to the c-axis of the crystals, negative magnetoresistance was observed. The highest value of negative magnetoresistance (AR/R(O) = - 1 ) was measured for the alloy of 30% atomic tin concentration and for H oriented at 60 ° with respect to the c-axis of the monocrystal. There is no evidence of negative magnetoresistance
235
when applying low magnetic fields. We believe that the negative magnetoresistance behaviour in InaSn alloys can be explained theoreticaUy on the results [1] for the third-band electronic structure of the InaSn alloys.
References [ 1] S. Maciejewskiand M. Surma, Acta Phys. Polon. A51 (1977) 265.