MÖSSBAUER EFFECT OF SrLnFeO4 (Ln=La, Pr, Nd)

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MÖSSBAUER EFFECT OF SrLnFeO4 (Ln=La, Pr, Nd)

M. Shimada, M. Koizumi, M. Takano, T. Shinjo, T. Takada

To cite this version:

M. Shimada, M. Koizumi, M. Takano, T. Shinjo, T. Takada. MÖSSBAUER EFFECT OF SrL- nFeO4 (Ln=La, Pr, Nd). Journal de Physique Colloques, 1979, 40 (C2), pp.C2-272-C2-274.

�10.1051/jphyscol:1979296�. �jpa-00218687�

JOURNAL DE PHYSIQUE Colloque Cl, supplément au n° 3, Tome 40, mars 1979, page C2-272

MOSSBAUER EFFECT OF S

L

F

0

(Ln=La/ Pr, Nd)

M. Shimada, M. Koizumi, M. Takano , T. Shmjo and T. Takada

The Institute of Scientific and Industrial Research, Osaka University, Osaka, Japan

* Department of Chemistry, Faculty of Science, Konan University, Kobe, Japan

**Institute for Chemical Research, Kyoto University, Uji, Kyoto-fu, Japan

Résumé.- On a étudié par effet Mossbauer les composés SrLaFeC»!,, SrPrFeO et SrNdFeO,, de structure KjNiF^ entre 4 K et 640 K. Les données combinées relatives aux interactions quadrupolaire et magné-

tique indiquent qu'il existe un phénomène de réorientation de spin autour de 77 K dans SrPrFeO^ et SrNdFeO,,. Le phénomène n'apparaît pas dans SrLaFeO^.

Abstract.- The Mossbauer effect has been studied in SrLaFeO!,, SrPrFeO^ and SrNdFeO,, with K ^ i F ^ structure in the temperature range between 4 K and 640 K. The results of the combined magnetic and quadrupole interactions indicated that SrPrFeO,, and SrNdFeO,, exhibited spin re-orientation phenomena at about 77 K. On the other hand, no spin reorientation was found in SrLaFeO,,.

1. Introduction.- In recent years, theoretical and experimental studies have been made on two dimensio- nal magnetic systems. The family of planar compounds with K2NiF,, structure seems to be one of the most promising compounds with two dimensional structure.

Although many studies on magnetic properties of the fluorides have been reported /1,4/, there have been only a few investigations on the oxides /5,6/. Re-

cently, Joubert et al. Ill synthesized the new oxi- des of SrLnFeO,, (Ln=La, Pr, Sm, Eu, Gd, Tb) with K2NiF, structure, but no magnetic properties of the- se oxides have been reported.

In the present note, Mossbauer results on SrLaFeO,,, SrPrFeO,, and SrNdFeO,, are described and the spin reorientation phenomena of SrPrFeO>4 and SrNdFeO,, are reported.

2. Experimental.- Powdered specimens were synthe- sized from analytical reagent grade a-Fe203, SrC03

and Ln203 (Ln=La, Pr, Nd) by using standard ceramic techniques. After calcining them in air or in a stream of Ar gas at 1100-1300°C for 100 hours, the samples were annealed at 400°C under a high oxygen pressure of 1000 bar. The products were identified by X-ray powder diffraction. Magnetic susceptibility measurements were carried out using a conventional magnetic torsion balance from 4.2 K to 300 K in a field of 8 kOe. The Mossbauer effects were measured in the temperature range between 4.2 K and 640 K.

57

The gamma ray source, Co doped in Cu metal, was always kept at room temperature. Calibration of ve- locity was made by using pure Fe metal as standard absorber-

3. Results and discussion.- The X-ray powder diffrac-

tion patterns of products were completely indexed as the K2NiF,, structure. The lattice parameters of each

o o sample were calculated to be a=3.880A, c=12.687Afor SrLaFeO.,, a=3.861A, c=12.554A for SrPrFeO., and a=

3.855 A, c=12.5 35A for SrNdFeO.,. The temperature dependence of the magnetic susceptibility did not show any anomaly due to the magnetic ordering as shown in figure 1.

Fig. 1 : The temperature dependence of the inverse magnetic susceptibility.

However, magnetic hyperfine spectra were found at low temperature as shown in figures 2-4.

In the paramagnetic state, the intensities of the two lines are not the same but the lower energy line is larger than the higher one.

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1979296

Velocity ( m m h f Fig. 2 : Mzssbauer s p e c t r a of SrLaFeO,

.

I l l f ' " ' I i I

-10 -8 -6 -4 -2 0 2 4 6 8 10 Velocity ( mmls )

Fig. 4 : Mzssbauer s p e c t r a of SrNdFeO,.

1 1 ~ ~ ~ 1 1 ~ 1 1 1

-10 - 8 -6 - 4 -2 0 2 4 6 8 10 Velocity (mmls 1

Fig. 3 : Mzssbauer s p e c t r a of SrPrFeO,.

A s shown i n f i g u r e 4 , t h e paramagnetic d o u b l e t of SrNdFeO i s o b v i o u s l y a s y m n e t r i c a t 300 K bllt becorns r a t h e r symmetric w i t h t h e i n c r e a s e of t h e temperature.

T h i s r e s u l t probably i s n o t accounted f o r by t h e t e x t u r e e f f e c t , b u t by t h e r e l a x a t i o n e f f e c t of t h e m a g n e t i c s p i n s .

From t h e t e m p e r a t u r e dependences of t h e i n t e r - n a l m a g n e t i c f i e l d , t h e magnetic o r d e r i n g temperatu- r e s were e s t i m a t e d t o b e around 330 K f o r SrLaFeO,, 250 K f o r SrPrFeO, and 270 K f o r SrNdFeO,. Although t h e parameter AS= S1-S2 ( s e e t h e f i g u r e s ) was posi- t i v e f o r each sample a t above 110 K and was n e a r l y e q u a l t o t h e quadrupole s p l i t t i n g i n t h e paramagne- t i c s t a t e , t h e s i g n s of AS a t 4 K of SrPrFeO, and SrNdFeO, were o p p o s i t e and n e a r l y twice a s l a r g e a s AS a t 110 K a s shown i n f i g u r e s 3 and 4. On t h e o t h e r hand, AS of SrLaFeO, was a c t u a l l y t e m p e r a t u r e independent i n d i c a t i n g no s p i n r e - o r i e n t a t i o n . These r e s u l t s i n d i c a t e d t h a t SrPrFeO, and SrNdFeO, have s p i n r e - o r i e n t a t i o n phenomena between 4

K

The m a g n e t i c h y p e r f i n e s p e c t r a of t h e s e o x i d e s a t 77 K which show t h e superpose of two s i x - l i n e s sug- g e s t t h a t t h e s p i n t u r n s d i s c o n t i n u o u s l y from t h e c-plane t o t h e c-axis w i t h t h e d e c r e a s e of t h e tem- p e r a t u r e .

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