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Neutron diffraction and magnetic measurements of polycrystalline NH4MnCl3
Solid State Communications,
Vol. 9, pp. 493—495, 1971
Pergamon Press.
Printed in Great Britain
NEUTRON DIFFRACTION AND MAGNETIC MEASUREMENTS OF POLYCRYSTALLINE NH4MnC13 G. Shachar,
J. Makovsky
and H. Shaked
Department of Physics, Nuclear Research Centre— Negev P.O.B. 9001, Beer—Sheva, Israel (Received 2 October 1970 by E.F. Bertaut)
Neutron diffraction and magnetic susceptibility measurements show NH4 MnCI3 to be an antiferromagnet of type G with TN 105°K.The low temperatute patterns reveal a tetragonal splitting and superlattice lines which were accounted for by assuming the space group to be Pbnrn. 7 of 1.03 A was taken. By minimizing factor a Debye—Wailer constant of 2.2 A2 the was Robtained. The final R factor was 0.053.
THE CHLORIDES of investigated formula AMnCI3 (A last = Na, K, Rb, Cs and Ti) were in the decade by various techniques.~3Recently, another compound of this composition, NH 4MnCI3, was prepared and found to have the cubic perovskite structure (space group Pm3m )~4 The present communication reports on magnetic susceptibility and neutron diffraction measurements on polycrystalline samples of NH4MnCI3. The measurements of the magnetic susceptibility were performed with a vibrating sample magnetometer. These measurements showed NH4 MnC13 to be an antiferromagnet with a Néel temperature of 110 ±15°K. The neutron diffraction patterns (Fig. 1) are characterized by very high background counts which are due to the incoherent scattering of the hydrogen nuclei. The room temperature data (Fig. la) was indexed on theA. 4with a = 5.057 basisobserved of the cubic unit cell integrated intensities The and calculated are compared in Table. 1. In the calculations the N, Mn and Cl ions were located respectively at the corners (site a), center (site b) and face centers (site c) of the unit cell (space group 5 Pm3m). Alperin and Nathans. the four Following H ions werePickart, randomly distributed on the diagonals connecting an N ions with its 12 neighbouring chlorine ions (site 121). For RN..W, the mean nitrogen—hydrogen distance, the value6 493
The diffraction pattern taken at 4.2°K (Fig. ib) exhibits additional lines and also a splitting of the (cubic) tOO2t line. The pattern was indexed on the basis of a~tetragona1unit cell containing four formula units with a = 7.05 A and c = 10.23 A (c/a~/2 = 1.03) which gave a good fit to all observed lines. Indices of weak lines for which the calculated intensities are less than 2 per cent of the strongest irne, were omitted from Fig. lb. An alternative unit cell with a 720A and c = 9.93 A (c/a~/2 = 0.98) fits the data only poorly and seems inappropriate. The temperature dependence of the (tetragonal) lOut line yielded a transition temperature of 100 ±lO°K,in agreement with the Ned temperature deduced from the magnetic susceptibility measurements. The appearance of the toil I magnetic line indicates’ that NH 4MnC19is an antiferromagnet of mode G in which the six neatest neighbours of each spin are antiparallel to it. The magnetic reflections of mode 0 (and only of mode G) are characterized by h + k odd and 1 odd. The appearance of the non-magnetic 11221 line (Fig. ib) is attributed to a
494
MEASUREMENTS OF POLYCRYSTALLINE NFl4 MnCI3 C’.
C’~ ..~
—
~L
C’. —
C’.
NH~M~LL~
~iij
z
Vol. 9, No. 9
-
~
~F 4.2 °V
4
PL
Z3f
10
15
—— 25 sc~TTEs:N~~3LE.22
-
35
~EG
FIG. 1. Neutron diffraction patt~rns(A = 1.02 A) of NH4MnC13. a At 300°K,the indices correspond to the cubic cell with a = 5.057 A. b At 4.2°K,the indices correspond to the tetragonal cell with a = b= 7.05A and c = 1O.23A. —
—
crystallographic distortion. A relatively strong 11221 distortion line 3 was observed in other ~ for which also the space distorted perovskites group Pbnm (D~) was chosen as the most
Mn : (4b) 1/2 0 0 1/2 0 1/2 0 1/2 0 0 1/2 1/ Cl1 : x(4c)± (x y y1/4 1/2 x 1/2 y 1/4) with = 0.04 = 0.50 Cl 11: (8d)±(x y z 1/2 x 1/2 + y 1/2 z z 1/2 z 1/2 x 1/2 y !) with x 0.29 y = 0 29 z = 0 N (4c) with x = y = 0 —
~-
—
probable. Accordingly, the low temperature data of NH4 MnC13 was analyzed assuming that it belongs to Pbnm, The observed and calculated integrated intensities are presented in Table 2. The intensities were calculated using the following sites in Pbnm:
-t
—
+
The sixteen hydrogen ions were randomly distributed at 48 positions (sited 8d) around the
Table 1. Observed and calculated integrated intensities of NH4MnC13 at room temperature. The indices correspond to the cubic unit cell with a0 = 5.057 A. The numbers in parentheses are the estimated standard deviations.
thklt
001
011
‘obs
29(4) 34
104(4) 78
111
002
022
297(3) 311
126(4) 132
148(4) 149
222 296(6) 296
Vol. 9, No. 9
MEASUREMENTS OF POLYCRYSTALLINE NH4MnCI3
Table 2. Observed and calculated integrated intensities of NH4MnCi~at 4.2°K. The indices correspond to the tetragonal cell with a = b = 7.O5Aandc= l0.23A. For each peakonly the indices ofinthe strongest are lines listed. The numbers parentheses thea~e estimated standard deviations,
495
N ions, on the lines connecting the N ions with the Cl ions with RN.~= 1.03 A. The magnetic contribution was calculated for mode 0 with a 5’~B• Minimizing R with magnetictomoment respect x(CL of 4), x(C111) and y(Cl11) resulted in an R value of 0.150. The parameters which yield a minimal R are not unique: R values of similar magnitude were obtained when the three parameters x(Cl1), x(C111) and y(Cl11) were changed by up to ±0.05. However, not all parametel combinations in this range yielded a low R value. .
.
.
I hkl I 011 002, 110 020
93(3) 16(2)
si
013, 121 022 122 004
32(2) 245(2) 32(2) 56(2)
53 215 17 38
For example: Placing the chlorine ions in the ideal positions x(C11)=O, x(Cl11)= 0.25, y(Cl11) = 0.25 led to an R value of 0.369. Intensity calculations for the alternative unit cell (with
033 224, 330, 026,
85(3) 66(3) 232(4)
105 83 240
c < a ~/2 ) did not improve the R value. It is hoped that measurements on deuterated samples and/or single crystals will lead to a fuller determination of the crystallographic and magnetic structure of NH4MnC13.
231 040 142 242
‘obii
‘ciii
20
REFERENCES 1.
KESTIGIAN M. and CROFT W.J., Mat. Res. Bull. 4, 877 (1969).
2.
MCMURDIE H.F., DE GROOT
3. 4.
MELAMUD M., PINTO H., SHACHAR G., MAKOVSKY J. and SHAKED H., J. Phys. to be published (Proc. 1970 un. Conf. Magnetism). AMIT M., ZODKEVITZ Z. and MAKOVSKY J., Israel J. Chem., to be published.
5.
PICKART S.J., ALPERIN H.A. and NATHANS R., J. Phys. 25, 565 (1964).
6.
LEVY H.A. and PETERSON S.W., Phys. Rev. 86, 766 (1952).
7
R
8. 9.
The Debye Wailer Constant B is defined by K = 1~e~ BERTAUT E.F., Acta Crystallogr. A24, 217 (1968).
— -
~
J., MORRIS M.
and SWANSON H.E., J. Res. NBS, 73A, 621 (1969).
lobs ‘call Itobs
2’~’~2~ 10.
SCATTURIN V., CORLISS L., ELLIOTT W. and HASTINGS
11.
The spin direction can not be deduced from our data.
J., Acta
Ciystallogr. 14, 19 (1961).
La diffraction des neutrons et des mesures de susceptibilité magnetique montrent que NH 4MnC13 est antiferromagnetique du type 0 avec TN 105°K. -‘~
Le spectre de diffraction a basse temperature rCvCle une déformation quadratique sinsi que des raies de surstructure dont on peut rendre compte en supposant que la structure appartient au groupe spatial Pbnm.
Vol. 9, pp. 493—495, 1971
Pergamon Press.
Printed in Great Britain
NEUTRON DIFFRACTION AND MAGNETIC MEASUREMENTS OF POLYCRYSTALLINE NH4MnC13 G. Shachar,
J. Makovsky
and H. Shaked
Department of Physics, Nuclear Research Centre— Negev P.O.B. 9001, Beer—Sheva, Israel (Received 2 October 1970 by E.F. Bertaut)
Neutron diffraction and magnetic susceptibility measurements show NH4 MnCI3 to be an antiferromagnet of type G with TN 105°K.The low temperatute patterns reveal a tetragonal splitting and superlattice lines which were accounted for by assuming the space group to be Pbnrn. 7 of 1.03 A was taken. By minimizing factor a Debye—Wailer constant of 2.2 A2 the was Robtained. The final R factor was 0.053.
THE CHLORIDES of investigated formula AMnCI3 (A last = Na, K, Rb, Cs and Ti) were in the decade by various techniques.~3Recently, another compound of this composition, NH 4MnCI3, was prepared and found to have the cubic perovskite structure (space group Pm3m )~4 The present communication reports on magnetic susceptibility and neutron diffraction measurements on polycrystalline samples of NH4MnCI3. The measurements of the magnetic susceptibility were performed with a vibrating sample magnetometer. These measurements showed NH4 MnC13 to be an antiferromagnet with a Néel temperature of 110 ±15°K. The neutron diffraction patterns (Fig. 1) are characterized by very high background counts which are due to the incoherent scattering of the hydrogen nuclei. The room temperature data (Fig. la) was indexed on theA. 4with a = 5.057 basisobserved of the cubic unit cell integrated intensities The and calculated are compared in Table. 1. In the calculations the N, Mn and Cl ions were located respectively at the corners (site a), center (site b) and face centers (site c) of the unit cell (space group 5 Pm3m). Alperin and Nathans. the four Following H ions werePickart, randomly distributed on the diagonals connecting an N ions with its 12 neighbouring chlorine ions (site 121). For RN..W, the mean nitrogen—hydrogen distance, the value6 493
The diffraction pattern taken at 4.2°K (Fig. ib) exhibits additional lines and also a splitting of the (cubic) tOO2t line. The pattern was indexed on the basis of a~tetragona1unit cell containing four formula units with a = 7.05 A and c = 10.23 A (c/a~/2 = 1.03) which gave a good fit to all observed lines. Indices of weak lines for which the calculated intensities are less than 2 per cent of the strongest irne, were omitted from Fig. lb. An alternative unit cell with a 720A and c = 9.93 A (c/a~/2 = 0.98) fits the data only poorly and seems inappropriate. The temperature dependence of the (tetragonal) lOut line yielded a transition temperature of 100 ±lO°K,in agreement with the Ned temperature deduced from the magnetic susceptibility measurements. The appearance of the toil I magnetic line indicates’ that NH 4MnC19is an antiferromagnet of mode G in which the six neatest neighbours of each spin are antiparallel to it. The magnetic reflections of mode 0 (and only of mode G) are characterized by h + k odd and 1 odd. The appearance of the non-magnetic 11221 line (Fig. ib) is attributed to a
494
MEASUREMENTS OF POLYCRYSTALLINE NFl4 MnCI3 C’.
C’~ ..~
—
~L
C’. —
C’.
NH~M~LL~
~iij
z
Vol. 9, No. 9
-
~
~F 4.2 °V
4
PL
Z3f
10
15
—— 25 sc~TTEs:N~~3LE.22
-
35
~EG
FIG. 1. Neutron diffraction patt~rns(A = 1.02 A) of NH4MnC13. a At 300°K,the indices correspond to the cubic cell with a = 5.057 A. b At 4.2°K,the indices correspond to the tetragonal cell with a = b= 7.05A and c = 1O.23A. —
—
crystallographic distortion. A relatively strong 11221 distortion line 3 was observed in other ~ for which also the space distorted perovskites group Pbnm (D~) was chosen as the most
Mn : (4b) 1/2 0 0 1/2 0 1/2 0 1/2 0 0 1/2 1/ Cl1 : x(4c)± (x y y1/4 1/2 x 1/2 y 1/4) with = 0.04 = 0.50 Cl 11: (8d)±(x y z 1/2 x 1/2 + y 1/2 z z 1/2 z 1/2 x 1/2 y !) with x 0.29 y = 0 29 z = 0 N (4c) with x = y = 0 —
~-
—
probable. Accordingly, the low temperature data of NH4 MnC13 was analyzed assuming that it belongs to Pbnm, The observed and calculated integrated intensities are presented in Table 2. The intensities were calculated using the following sites in Pbnm:
-t
—
+
The sixteen hydrogen ions were randomly distributed at 48 positions (sited 8d) around the
Table 1. Observed and calculated integrated intensities of NH4MnC13 at room temperature. The indices correspond to the cubic unit cell with a0 = 5.057 A. The numbers in parentheses are the estimated standard deviations.
thklt
001
011
‘obs
29(4) 34
104(4) 78
111
002
022
297(3) 311
126(4) 132
148(4) 149
222 296(6) 296
Vol. 9, No. 9
MEASUREMENTS OF POLYCRYSTALLINE NH4MnCI3
Table 2. Observed and calculated integrated intensities of NH4MnCi~at 4.2°K. The indices correspond to the tetragonal cell with a = b = 7.O5Aandc= l0.23A. For each peakonly the indices ofinthe strongest are lines listed. The numbers parentheses thea~e estimated standard deviations,
495
N ions, on the lines connecting the N ions with the Cl ions with RN.~= 1.03 A. The magnetic contribution was calculated for mode 0 with a 5’~B• Minimizing R with magnetictomoment respect x(CL of 4), x(C111) and y(Cl11) resulted in an R value of 0.150. The parameters which yield a minimal R are not unique: R values of similar magnitude were obtained when the three parameters x(Cl1), x(C111) and y(Cl11) were changed by up to ±0.05. However, not all parametel combinations in this range yielded a low R value. .
.
.
I hkl I 011 002, 110 020
93(3) 16(2)
si
013, 121 022 122 004
32(2) 245(2) 32(2) 56(2)
53 215 17 38
For example: Placing the chlorine ions in the ideal positions x(C11)=O, x(Cl11)= 0.25, y(Cl11) = 0.25 led to an R value of 0.369. Intensity calculations for the alternative unit cell (with
033 224, 330, 026,
85(3) 66(3) 232(4)
105 83 240
c < a ~/2 ) did not improve the R value. It is hoped that measurements on deuterated samples and/or single crystals will lead to a fuller determination of the crystallographic and magnetic structure of NH4MnC13.
231 040 142 242
‘obii
‘ciii
20
REFERENCES 1.
KESTIGIAN M. and CROFT W.J., Mat. Res. Bull. 4, 877 (1969).
2.
MCMURDIE H.F., DE GROOT
3. 4.
MELAMUD M., PINTO H., SHACHAR G., MAKOVSKY J. and SHAKED H., J. Phys. to be published (Proc. 1970 un. Conf. Magnetism). AMIT M., ZODKEVITZ Z. and MAKOVSKY J., Israel J. Chem., to be published.
5.
PICKART S.J., ALPERIN H.A. and NATHANS R., J. Phys. 25, 565 (1964).
6.
LEVY H.A. and PETERSON S.W., Phys. Rev. 86, 766 (1952).
7
R
8. 9.
The Debye Wailer Constant B is defined by K = 1~e~ BERTAUT E.F., Acta Crystallogr. A24, 217 (1968).
— -
~
J., MORRIS M.
and SWANSON H.E., J. Res. NBS, 73A, 621 (1969).
lobs ‘call Itobs
2’~’~2~ 10.
SCATTURIN V., CORLISS L., ELLIOTT W. and HASTINGS
11.
The spin direction can not be deduced from our data.
J., Acta
Ciystallogr. 14, 19 (1961).
La diffraction des neutrons et des mesures de susceptibilité magnetique montrent que NH 4MnC13 est antiferromagnetique du type 0 avec TN 105°K. -‘~
Le spectre de diffraction a basse temperature rCvCle une déformation quadratique sinsi que des raies de surstructure dont on peut rendre compte en supposant que la structure appartient au groupe spatial Pbnm.