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Magnetic properties of antiferromagnetic Nd monochalcogenides
PHYSICS
Volume 29A, number 10
LETTERS
11 August 1969
vacuum). A more detailed description of this process will be published later.
this result coincides with that of Ltithi [l], as expected, since only the coherent part of the final state contributes to the expectation of the magnetization. In large non-ellipsoidal samples the magnetizing field is non-uniform and plays a very important role in the excitation mechanism [2]. In this case there is an additional term in the Hamiltonian which is quadratic in the magnon operators and for t > 0 we do not have a pure coherent state (even if the initial state is the
References 1. B. Ltithi, J. Appl. Phys. 33 (1962) 244. 2. E. Schlbmann, J. Appl.Phys. 35 (1964) 159. 3. S. M. Rezende and N. Zagury, Phys. Letters 29A (1969) 47. 4. M. Sparks, Ferromagnetic relaxation theory (Mac Graw Hill Book Co., New York, 1964). 5. Glauber, Phys. Rev. 131 (1963) 2766.
*****
MAGNETIC ANTIFERROMAGNETIC
PROPERTIES OF Nd MONOCHALCOGENIDES
A. T. STARGVOITOV, V. I. OZHOGIN and G. M. LOGINOV Institute
of Semiconductors
of the Academy of Sciences, Received
Leningrad,
USSR
19 June 1969
It has been shown that for neodimium monochalcogenides (NdX, X = S, Se, Te) the critical field of - 90 kOe induces an antiferromagnet-ferromagnet transition at 4.2 and l.S”R. The maximum values of the induced moment are lower than the free-ion value (gjfl= 3.26) and close to the value of the ferromagnetic moment for the lowest energy level, which is r6 doublet in this case.
with negative e’s, the values of effective magnetic moment ggpp? = 2.84@M#? bein close to that calculated for the ground state gJ; of free Nd3+ ion (table 1). It has been found also that at -1OoK x-l(T) curves of the discussed compounds had a sharp minimum which was interpreted as indicative of the antiferromagnetic transition. The corresponding N6el points are given in column 5 of table 1. In column 6, the table containes also the values of NQel points obtained from kinetic properties [6]. The fact that the antiferromagnetic ordering occurs at sufficiently low temperatures has made possible the study of field-induced antiferromagnet-ferromagnet transition in fields below 250 kOe as it was also in the case of HoAs, ErAs, DyAs, TbAs, EuTe [7], and NdP-NdAs [8].
The magnetization of monochalcogenides NdX(X = S, Se, Te) was investigated in pulsed fields up to 230 kOe at 4.2 and 1.6OK. Measurements were performed by the induction method [1,2]. The monochalcogenides were synthesized by a direct reaction between elements [3]. Metallic Nd and chalcogens were 99.5 and 99.990/0 of purity, respectively. As indicated by X-ray diffraction data, the samples were single-phase with well-performed NaCl structure. The lattice parameters of the compounds are given in table 1. Recent magnetic measurements in C 15 kOe static fields have shown [4,5] that down to - 70oK, all Nd monochalcogenides have magnetic susceptibility following the Curie-Weiss law x = C/(T-0)
Table 1 NdX
NdS
0
exp cr eff 0
3.62
3.62
CLeff= #2+J+
5.63
ax103
AE
TN [51
TN [61
(OR)
(OR)
(8)
#Woe)
(OR)
8
8.2
1.12
2.8
60
Mind
NdSe
5.90
3.62
3.52
14
10.6
1.33
4.8
50
NdTe
6.26
3.62
3.54
13
10.2
1.29
4.8
50
617
Volume 29A, number
10
PHYSICS
00
,DD ff,
.?I?0
Fig. 1. Magnetic moment versus field for NdX. X = = S -0,O; Se - 0; Te - A,A at 1.6 and 4.2oK. resoectively. .
data m(H) measured NdTe, m(H) is seen a sharp rising at tical field H, - 80-90 kOe and Magnetization versus field at 1.6eK shown in fig.
lMind
11 August 1969
The differential susceptibility is due to both polarization of the lowest energy level (by admixture of above-lying ones) and the magnetization of conducting electrons whose concentration may be - 1O22 cmv3. The 250 kOe change of magnetic moment caused by xel can be estimated as Amel - O.Olp. It can be thus concluded that the main contribution to xd is given by admixture of nearest above-lying F8 quartet. The corresponding energy correction is AW = = (Mind I$12/AE. It follows that x = 2Mzd /AE where AE is F6 - F8 energy separation. Such a crude estimate gives, however, a rather reasonable value AE - 50°K [9]. Some gain in AE observed from NdTe to NdS may be accounted for by considering the crystalline-field effect which is due to both the lattice parameter decrease and the anion negativity increase.
.+-a*
) NdSe and NdTe
LETTERS
have
Volume 29A, number 10
LETTERS
11 August 1969
vacuum). A more detailed description of this process will be published later.
this result coincides with that of Ltithi [l], as expected, since only the coherent part of the final state contributes to the expectation of the magnetization. In large non-ellipsoidal samples the magnetizing field is non-uniform and plays a very important role in the excitation mechanism [2]. In this case there is an additional term in the Hamiltonian which is quadratic in the magnon operators and for t > 0 we do not have a pure coherent state (even if the initial state is the
References 1. B. Ltithi, J. Appl. Phys. 33 (1962) 244. 2. E. Schlbmann, J. Appl.Phys. 35 (1964) 159. 3. S. M. Rezende and N. Zagury, Phys. Letters 29A (1969) 47. 4. M. Sparks, Ferromagnetic relaxation theory (Mac Graw Hill Book Co., New York, 1964). 5. Glauber, Phys. Rev. 131 (1963) 2766.
*****
MAGNETIC ANTIFERROMAGNETIC
PROPERTIES OF Nd MONOCHALCOGENIDES
A. T. STARGVOITOV, V. I. OZHOGIN and G. M. LOGINOV Institute
of Semiconductors
of the Academy of Sciences, Received
Leningrad,
USSR
19 June 1969
It has been shown that for neodimium monochalcogenides (NdX, X = S, Se, Te) the critical field of - 90 kOe induces an antiferromagnet-ferromagnet transition at 4.2 and l.S”R. The maximum values of the induced moment are lower than the free-ion value (gjfl= 3.26) and close to the value of the ferromagnetic moment for the lowest energy level, which is r6 doublet in this case.
with negative e’s, the values of effective magnetic moment ggpp? = 2.84@M#? bein close to that calculated for the ground state gJ; of free Nd3+ ion (table 1). It has been found also that at -1OoK x-l(T) curves of the discussed compounds had a sharp minimum which was interpreted as indicative of the antiferromagnetic transition. The corresponding N6el points are given in column 5 of table 1. In column 6, the table containes also the values of NQel points obtained from kinetic properties [6]. The fact that the antiferromagnetic ordering occurs at sufficiently low temperatures has made possible the study of field-induced antiferromagnet-ferromagnet transition in fields below 250 kOe as it was also in the case of HoAs, ErAs, DyAs, TbAs, EuTe [7], and NdP-NdAs [8].
The magnetization of monochalcogenides NdX(X = S, Se, Te) was investigated in pulsed fields up to 230 kOe at 4.2 and 1.6OK. Measurements were performed by the induction method [1,2]. The monochalcogenides were synthesized by a direct reaction between elements [3]. Metallic Nd and chalcogens were 99.5 and 99.990/0 of purity, respectively. As indicated by X-ray diffraction data, the samples were single-phase with well-performed NaCl structure. The lattice parameters of the compounds are given in table 1. Recent magnetic measurements in C 15 kOe static fields have shown [4,5] that down to - 70oK, all Nd monochalcogenides have magnetic susceptibility following the Curie-Weiss law x = C/(T-0)
Table 1 NdX
NdS
0
exp cr eff 0
3.62
3.62
CLeff= #2+J+
5.63
ax103
AE
TN [51
TN [61
(OR)
(OR)
(8)
#Woe)
(OR)
8
8.2
1.12
2.8
60
Mind
NdSe
5.90
3.62
3.52
14
10.6
1.33
4.8
50
NdTe
6.26
3.62
3.54
13
10.2
1.29
4.8
50
617
Volume 29A, number
10
PHYSICS
00
,DD ff,
.?I?0
Fig. 1. Magnetic moment versus field for NdX. X = = S -0,O; Se - 0; Te - A,A at 1.6 and 4.2oK. resoectively. .
data m(H) measured NdTe, m(H) is seen a sharp rising at tical field H, - 80-90 kOe and Magnetization versus field at 1.6eK shown in fig.
lMind
11 August 1969
The differential susceptibility is due to both polarization of the lowest energy level (by admixture of above-lying ones) and the magnetization of conducting electrons whose concentration may be - 1O22 cmv3. The 250 kOe change of magnetic moment caused by xel can be estimated as Amel - O.Olp. It can be thus concluded that the main contribution to xd is given by admixture of nearest above-lying F8 quartet. The corresponding energy correction is AW = = (Mind I$12/AE. It follows that x = 2Mzd /AE where AE is F6 - F8 energy separation. Such a crude estimate gives, however, a rather reasonable value AE - 50°K [9]. Some gain in AE observed from NdTe to NdS may be accounted for by considering the crystalline-field effect which is due to both the lattice parameter decrease and the anion negativity increase.
.+-a*
) NdSe and NdTe
LETTERS
have