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Spin configuration of ErFeO3 below the ordering temperature of erbium
Solid State Communications,Vol. 15, pp. 1769—1771, 1974.
Pergamon Press.
Printed in Great Britain
SPIN CONFIGURATION OF ErFeO3 BELOW THE ORDERING TEMPERATURE OF ERBIUM V.M. Khmara, N.M. Kovtun and G.A. Troitskii Physico-Technical Institute of the Academy of Sciences of the Ukr.SSR, 340048 Donetsk, USSR (Received 7 June 1974 by E.A. Kaner) 51 spectra of ErFeO The NMR Fe 3 at liquid helium temperatures with and without external magnetic field along each of the three principal crystal axes are reported. A gradual spin rotation of iron ions is shown to take place in the bc;plane below T~2= 3.98 K. The difference in the orientation of iron spins which at T> TN2 were parallel is found.
FOR THE first time the configuration of erbium 1 On orthoferrite was investigated by data Koehier aL the basis of neutron diffraction theyetconcluded that erbium ions were ordered at TN = 4.3 K in the configuration C~,and iron ions at T = 1 .25°Khave
measurement of of NMR frequencies corresponding tothe thedifference ions with antiparallelly directed spins depending on the mutual arrangement of spins and external magnetic field i~f= 2’yH 0cosØ
Gxy spin configuration. Later the ordering temperature of rare-earth ions (TN2 = 4Q K) was made more precise and the 24 above spin configurations were confirmed. 5 it is However, in a recently reported paper shown that two different spin configurations Gxy and
where ‘y is the gyromagnetic ratio for the Fe 57 nuclei, H0 is the the external magnetic and field, between spin direction H ~ is the angle 0. The investigations were carried out using a spin— echo spectrometer and ErFeO 3 single crystals grown by the method described in reference 6. The durations of the exciting pulses satisfied the condition of the excitation of nuclei in domains and were equal to = lOLsec, r2 = 20isec. The NMR line width was about 45 kHz in this case. .
Gzy for iron ions may be consistent with neutron diffraction data obtained at T = 1 .5°K.In the first case the antiferromagnetic axis is in the ab-crystallographic plane at an angle 33 ±4°Kto the b-axis, and in the second case it is in the bc-plane at an angle ;5 I ±8°Kto the b-axis. Taking into account the orthogonality of the antiferromagnetic vector and weak ferromagnetic moment, and also the data of magnetic and torque measurements, according to which a weak ferromagnetic moment below the liquid nitrogen temperature is alongthat the in a-axis, Gorodetsky 5 arrive at a conclusion ErFeO et al. 3 at low temperatures iron spins have Gzy configuration but not Gxy.
.
The temperature dependence of the NMR fre51 in ErFeO quencies of Fe 3 in a zero magnetic field is shown in Fig. 1(a). It is seen that at TN2 = 3.98°K NMR line splitting takes place and that indicates the disturbance of equivalency of iron ions when the erbium sublattice is ordered. The external magnetic field H0 applied parallel to the a-crystal axis decreases slightly thetemperature of ordering of erbium ions TN2 but the character of temperature dependence of NMR frequencies remains the same: above TN2 one line is observed in the NMR spectrum, below this temperature two lines are
In the present paper the results of the NMR investigation which allow the direct determination of a spin configuration of iron ions are given. The determination method of a spin position consists in the 1769
1770
SPIN CONFIGURATION OF ErFeO3
~
Vol. 15, No. 11/12
8~ 50
75;,
IIIIIIIIIIII111I7~~~ ~
7j1~L
I~o
~
0,H~
_________________________________ 3~ions at T< TN 3.0andthe ‘1.0 the ~ between configuration FIG.2,0the 2. (a) theTemperature spin of Fe direction dependence thesplitting c-axis. 2.of the(b) 0 Spin angle with temperature decrease due to magnetic field, as it follows from Fig. 1, decreases at H0 II c and increases at H0 Ii b. It indicates the coherent rotation of spins from the c-axis to the b-axis.
75.9
~
75.’.
4°
75;c
75.5 75* 75.3 75.2
___________________________________ Z~
2.5
5,0
3.5
4,0~2l~
FIG. 1. Temperature dependence of NMR frequencies in ErFeO3 (a) H0 = 0; (b) H0 II c; H0 = 1.1 kOe; (c) H0 II b; H0 = 2 kOe. observed. The field H0 parallel to the c-axis [Fig. 1(b)] gives rise not only to the TN decrease but also the splitting of each of spectral lines. Figure 1(c) shows the influence of the field H0 which is parallel to the b-crystal axis, and it is seen that TN2 remains the same, and the number of lines in the NMR spectrum below TN2 doubles as compared with the case H0 = 0. From the data given in Fig. 1 it also follows that below the temperature TN2 each line in the NMR e ions spectrum = 0 in corresponds to a and pair 2,3). ofF ~ with spinsatH0 opposite direction (1,4
Aácording to the above formulae and using the data of Fig. 1(c) the temperature dependence of 0 (0 is the angle between the direction of the spins and the c-axis) is found [Fig. 2(a)]. The values of 0~and 02 angles obtained from the splitting of high and low spectral lines differ in magnitudes. When the temperature is decreased the difference between 01 and 02 increases, and at T = 2°Kit reaches 3~50• Taking account of these data 3~ions one may at T represent < TN the spin configuration of Fe 2 in the form given in Fig. 2(b). In this figure an alternative notation is given because NMR data do not permit to say definitely what an ion pair (1,4 or 2,3) corresponds to each of the spectral lines in Fig. 1(a). The difference of the angles 0~and 02 below TN2 cannot be explained by the influence of the external field, as the splitting due to the field when H0 is along the b-axis, at any temperature depends linearly on H0. The difference in the angles 0~and 02 seems to be due to3~ions nonequal influence of 1,4 a rare-earth in the positions and 2,3,sublattice respectively. on Fe Thus, the results of our investigations show that
As above TN
2 at H0 II a and H0 I b the NMR spectrum consists of one line and at H0 II c it consists of two lines one may conclude that above TN2 the spins of iron ions are along the c-axis. At T < TN2
coherent rotation of iron spins from the configuration Gz to the configuration Gzy takes place in ErFeO3 at low temperatures.
Vol. 15, No. 11/12
SPIN CONFIGURATION OF ErFeO3
1771
REFERENCES 1.
KOEHLER W.C., WOLLAN E.O. and WILKINSON M.K.,Phys. Rev. 118,58(1960).
2.
PATAUD P. and SNARDIERE J.,J. Phys. 31, 803 (1970).
3.
PEYRARD J. and SIVARDIERE J., Solid State Commun. 7, 605 (1969).
4.
BELAKHOVSKY M., SHAPPERT J., RUOSKOV J. and SIVARDIERE J.,J. Phys. 32,492(1971).
5.
GORODETSKY G., HORNREICH R.M., YAEGER I., PINTO H., SHACHAR G. and SHAKED H.,Phys. Rev. B8, 3398 (1973). ANTONOV A.V., BALBASHOV A.M. and CHERVONENKIS A.Ya.,Fiz. Tverd. Tela 12, 1724 (1970).
6.
Pergamon Press.
Printed in Great Britain
SPIN CONFIGURATION OF ErFeO3 BELOW THE ORDERING TEMPERATURE OF ERBIUM V.M. Khmara, N.M. Kovtun and G.A. Troitskii Physico-Technical Institute of the Academy of Sciences of the Ukr.SSR, 340048 Donetsk, USSR (Received 7 June 1974 by E.A. Kaner) 51 spectra of ErFeO The NMR Fe 3 at liquid helium temperatures with and without external magnetic field along each of the three principal crystal axes are reported. A gradual spin rotation of iron ions is shown to take place in the bc;plane below T~2= 3.98 K. The difference in the orientation of iron spins which at T> TN2 were parallel is found.
FOR THE first time the configuration of erbium 1 On orthoferrite was investigated by data Koehier aL the basis of neutron diffraction theyetconcluded that erbium ions were ordered at TN = 4.3 K in the configuration C~,and iron ions at T = 1 .25°Khave
measurement of of NMR frequencies corresponding tothe thedifference ions with antiparallelly directed spins depending on the mutual arrangement of spins and external magnetic field i~f= 2’yH 0cosØ
Gxy spin configuration. Later the ordering temperature of rare-earth ions (TN2 = 4Q K) was made more precise and the 24 above spin configurations were confirmed. 5 it is However, in a recently reported paper shown that two different spin configurations Gxy and
where ‘y is the gyromagnetic ratio for the Fe 57 nuclei, H0 is the the external magnetic and field, between spin direction H ~ is the angle 0. The investigations were carried out using a spin— echo spectrometer and ErFeO 3 single crystals grown by the method described in reference 6. The durations of the exciting pulses satisfied the condition of the excitation of nuclei in domains and were equal to = lOLsec, r2 = 20isec. The NMR line width was about 45 kHz in this case. .
Gzy for iron ions may be consistent with neutron diffraction data obtained at T = 1 .5°K.In the first case the antiferromagnetic axis is in the ab-crystallographic plane at an angle 33 ±4°Kto the b-axis, and in the second case it is in the bc-plane at an angle ;5 I ±8°Kto the b-axis. Taking into account the orthogonality of the antiferromagnetic vector and weak ferromagnetic moment, and also the data of magnetic and torque measurements, according to which a weak ferromagnetic moment below the liquid nitrogen temperature is alongthat the in a-axis, Gorodetsky 5 arrive at a conclusion ErFeO et al. 3 at low temperatures iron spins have Gzy configuration but not Gxy.
.
The temperature dependence of the NMR fre51 in ErFeO quencies of Fe 3 in a zero magnetic field is shown in Fig. 1(a). It is seen that at TN2 = 3.98°K NMR line splitting takes place and that indicates the disturbance of equivalency of iron ions when the erbium sublattice is ordered. The external magnetic field H0 applied parallel to the a-crystal axis decreases slightly thetemperature of ordering of erbium ions TN2 but the character of temperature dependence of NMR frequencies remains the same: above TN2 one line is observed in the NMR spectrum, below this temperature two lines are
In the present paper the results of the NMR investigation which allow the direct determination of a spin configuration of iron ions are given. The determination method of a spin position consists in the 1769
1770
SPIN CONFIGURATION OF ErFeO3
~
Vol. 15, No. 11/12
8~ 50
75;,
IIIIIIIIIIII111I7~~~ ~
7j1~L
I~o
~
0,H~
_________________________________ 3~ions at T< TN 3.0andthe ‘1.0 the ~ between configuration FIG.2,0the 2. (a) theTemperature spin of Fe direction dependence thesplitting c-axis. 2.of the(b) 0 Spin angle with temperature decrease due to magnetic field, as it follows from Fig. 1, decreases at H0 II c and increases at H0 Ii b. It indicates the coherent rotation of spins from the c-axis to the b-axis.
75.9
~
75.’.
4°
75;c
75.5 75* 75.3 75.2
___________________________________ Z~
2.5
5,0
3.5
4,0~2l~
FIG. 1. Temperature dependence of NMR frequencies in ErFeO3 (a) H0 = 0; (b) H0 II c; H0 = 1.1 kOe; (c) H0 II b; H0 = 2 kOe. observed. The field H0 parallel to the c-axis [Fig. 1(b)] gives rise not only to the TN decrease but also the splitting of each of spectral lines. Figure 1(c) shows the influence of the field H0 which is parallel to the b-crystal axis, and it is seen that TN2 remains the same, and the number of lines in the NMR spectrum below TN2 doubles as compared with the case H0 = 0. From the data given in Fig. 1 it also follows that below the temperature TN2 each line in the NMR e ions spectrum = 0 in corresponds to a and pair 2,3). ofF ~ with spinsatH0 opposite direction (1,4
Aácording to the above formulae and using the data of Fig. 1(c) the temperature dependence of 0 (0 is the angle between the direction of the spins and the c-axis) is found [Fig. 2(a)]. The values of 0~and 02 angles obtained from the splitting of high and low spectral lines differ in magnitudes. When the temperature is decreased the difference between 01 and 02 increases, and at T = 2°Kit reaches 3~50• Taking account of these data 3~ions one may at T represent < TN the spin configuration of Fe 2 in the form given in Fig. 2(b). In this figure an alternative notation is given because NMR data do not permit to say definitely what an ion pair (1,4 or 2,3) corresponds to each of the spectral lines in Fig. 1(a). The difference of the angles 0~and 02 below TN2 cannot be explained by the influence of the external field, as the splitting due to the field when H0 is along the b-axis, at any temperature depends linearly on H0. The difference in the angles 0~and 02 seems to be due to3~ions nonequal influence of 1,4 a rare-earth in the positions and 2,3,sublattice respectively. on Fe Thus, the results of our investigations show that
As above TN
2 at H0 II a and H0 I b the NMR spectrum consists of one line and at H0 II c it consists of two lines one may conclude that above TN2 the spins of iron ions are along the c-axis. At T < TN2
coherent rotation of iron spins from the configuration Gz to the configuration Gzy takes place in ErFeO3 at low temperatures.
Vol. 15, No. 11/12
SPIN CONFIGURATION OF ErFeO3
1771
REFERENCES 1.
KOEHLER W.C., WOLLAN E.O. and WILKINSON M.K.,Phys. Rev. 118,58(1960).
2.
PATAUD P. and SNARDIERE J.,J. Phys. 31, 803 (1970).
3.
PEYRARD J. and SIVARDIERE J., Solid State Commun. 7, 605 (1969).
4.
BELAKHOVSKY M., SHAPPERT J., RUOSKOV J. and SIVARDIERE J.,J. Phys. 32,492(1971).
5.
GORODETSKY G., HORNREICH R.M., YAEGER I., PINTO H., SHACHAR G. and SHAKED H.,Phys. Rev. B8, 3398 (1973). ANTONOV A.V., BALBASHOV A.M. and CHERVONENKIS A.Ya.,Fiz. Tverd. Tela 12, 1724 (1970).
6.