New transparent ferrimagnets and their magnetic properties near Curie point

Solid State Communications, Vol. 5, PP. 927- 931, 1967. Pergamon Press Ltd. Printed in Great Britain

NEW TRANSPARENT FERRIMAGNETS AND THEIR MAGNETIC PROPERTIES NEAR CURIE POINT L. P. Boky, P. P. Syrnikov, V. M. Yudin and G. A. Smolensky Semiconductors Institute Acad. Set. Leningrad, USSR (Received 22 September 1967 by G.W. Rathenau)

New transparent ferrimagnet single crystals of Rb(Ni~,Co,)F3 composition have been synthesized, the value of x changing in the range of 0 + 0. 3. RbNIF3 (T, = 139°K) has magnetic anisotropy of an “easy-plane” -type, and RbNI0,,Co0,3 F3 (T, = 109°K) of an “easy axis” -type. It is founçl 4/3 that andnear the Curie (T, point T)°’5relations there are for observed both substances. (T- T,) —

-

~

SEVERAL investigations’~ have been devoted to a lately discovered1 transparent ferrimagnet, RbNiF 3 , having a hexagonal structure. We have synthesized a number of single crystals of Rb(Ni1..~Co~)F3(x = 0-0.3) composition, which are also transparent ferrimagnets and of hexagonal structure. With the increase of x from 0 to 0. 3 the colour of the crystals changes from green to dark red. RbNiF8 has a plane of easy magnetization and Rb(Ni0.,Co0.3 )F3 an easy axis. * For intermediate compositions maybe a cone of easy magnetization exists,

perature control was 0. 1°K. The results of the experiments are given in Figs. 1 and 2. The measuremements were carried out in the direction of easy magnetization: perpendicularly to the hexagonal axis for RbNIF8, along it for RbNt0,7Co0.3 F3 (the Co content in this crystal was not determined directly; the formula given above corresponds to the initial charge). —

Since the dependence upon the difference (T T0) is studied, the accuracy of the method to determine the Curie point is of great importance, as well as the method to determine the values of ~1 and a,. The method to determine T0, a,, and Xo based on the representation 2 H/a coordinatesof the is considered magnetization by usdata to be in the a optimal one at present for ferro- and ferrimagnets. ~ ~ Curie points defined by us in this way for RbN1F 3 and RbN10,,Co0,3 F3 are equal to 139°K and 109°K, correspondingly. -

In the present investigation we studied temperature dependences of initial magnetic tion, susceptibility, a,, near the ~ Curie and spontaneous point. Our magnetizaaim was to determined y and ~ exponents when the expertmental data are presented in the form:

(T-T,) a,

—

(T0 T) -

—

-

and

The analysts of the experimental data given in Figs. 1 and 2 show that for RbNiF3 and RbNi0,,Co0,3 F3 the values of y and ~ are close to 4/3 and 0. 5, correspondingly. For the sake of comparison in Fig. 2 straight lines are drawn with a slope corresponding to ~ = 1/3 as obtained in the0 majority theories for and to y of= modern 1, corresponding to ferromagthe molenets, cular field theory. At 77°Kthe spontaneous inagnetization amounts to 16.4 and 16. 7 G-sec cm3g”1 for RbNIF 3 and RbNtO,?CoO.3 F3 respectively.

.

The relative accuracy of the magnetic measurements was about 1%, the accuracy of the temperature measurements and of the tem_____________

*The investigations of the torque curves conducted together show with Dr. Perekalina withantan anisometer that T.M, the type of magnetic sotropy of the two crystals does not change in the range from 77°Kto the Curie point, 927

928

NEW TRANSPARENT FERRIMAGNETS

H,Gs~

~

~1o3, R6 NLF

~H/O’~cr~11g 6~’fO3

/ 120K 123

HO

16

Vol. 5, No. 12

120

C,’

127

ilili s~ (1/132

1/1134

I

I

I

1,0

‘Ri~C~f~’

7rff

,‘.~,

~f2~~F;. E

S

•

Tc

• 1,0

8

If

1

14sf

H,Gs

23g H/~cs’f

__ ______ FIG. 1

2

5

III’ (J

Field dependence of the magnetization in a -H and a2 -H/a coordinates at various temperatues f~ RbN1F 3 and RbNi0,,,Co0,3 F~crystals.

3Xfl)J

In this case the data given for RbNiF 3 are more accurate than those given before. ~ For comparison a summary of known results on ferrimagnets is collected in Table 1. The values of y are close to 4/3 for all substances. The values of ~ are near 0. 5 in when spontaneous magnetizatiOn is investigated, and

near 1/3 when the magnetization of individual sublattices is studied. It is interesting to compare the functional relations as given by ~ and y obtained by different method for the same crystal. The presented data for YIG hardly can be cornpared, since T~= 559°K has been determined from magnetic 9 One measurements’° should also take ~ and into549°K account from NMR.

,

Vol. 5 No. 12

NEW TRANSPARENT FERRIMAGNETS

OjGs.rs3.~’

I

929

I

•Iö~ai~’g

‘P I

I

(i~r~,°ic

I

R5Ni

I

-

I

I

~

-,

/ /

I

(FTc)

FIG. 2 Temperature dependences of spontaneous magnetization and inverse magnetic susceptibility and logarithmic plots of a, vs. (T, T) and ~‘ vs. (T T,) for RbNiF 3 and RbNi0~7Co0.3F3 crystals.

-

-

that from NMR and Mossbauer’s effect the mean value of the internal field is determined. It should rather depend on a short and not on a long range correlation function such as the magnetization measured in neutron diffraction and magnetometer experiments. The difference in mean

values of these functions has lately been shown. ~

-

Acknowled~ement The authors express their thanks to Miss Lyuda Kuznetzova for her help in carrying out the work.

930

NEW TRANSPARENT FERRIMAGNETS

Vol. 5, No. 12

TABLE 1 Experimental values for ~ and x~’~

y

in the expressions a,

Fet~imagnet T~(°lc) (tetv~ 549

0,32

(octa)

Rej.

035-085 05 - 48 Q9 - t05

NP1R

9

o(H) ef Mae.

10

559

0,28

0,5-093

(octa) LtFeC,.,~0~ ~ ~etzg) (octa) 985

0,32

0,35-0,93

0,28 0,34

0,5 - 0,85 0,5-0,85

Ni Fe2 04

130137

t1n,~~ F~0,,

1,31

GaFeO3

1,96

139

q5

02Co~3f3109

0,5

R6tVIF3

11 If 12

1,35

2O,~ lL~~xFe20~

R&Ni

“

2(H/0)

o’

1,32

t1nFe

-

riethod

Ni Fe~04 858

0$

(T, T) ~ and

T/Tc’uinpe

027 OfiS

YIG

—

0’ (ii)

1,33

0,6/fri 05

1,33

0,82-i08

2(H/~)

13 14

0’

n

References 1.

SMOLENSKY G.A., YUDIN V.M., Pis’ma, 3, 416 (1966).

2.

GOLOVENTCHITZ E.I., 3, 408 (1966).

3.

SMOLENSKY G.A., 8, 2965 (1966). SMOLENSKY G.A., (1967).

4.

SYRNIKOV P.P. and SHERMAN A.B.. Zh. Eksper. Teor. Ft

GUREVICH A.G. and SANINA V.A.,

YUDIN V.M.,

Zh. Eksper. Teor. Fiz., Pisma,

SYRNIKOV P.P. and SHERMAN A.B., Ftz. Tverd. Tela,

PISAREV R.V. and SINY I.G.,

5.

SHAFER M., McGUIRE T.R.,

6.

BELOV K. P.,

7.

Bureau Enterprises, Inc., N.Y. (1961). KOUVEL J.S. and FISHER M.E., Phys. Rev.

8.

CALLEN E. and CALLEN H.,

Zh. Eksper. Teor. Fiz., Pis’ma, 5, 96

ARGYLE B.E. and FAN G.I., Appl. Phys. Lett., 10, 202 (1967

Magnetic Transition, (Moscow, 1959), Translation from Russian. 136, A1626 (1964).

J. Appl. Phys. 36,

1140 (1965).

Consultants

931 9.

NEW TRANSPARENT FERRIMAGNETS LITSTER J.D.,

and BENEDEK G.B.,

10. ANDERSON E.,

Phys. Rev. Left.

11. VAN LOEF J. J., 12. BELOV K. P.,

17, 375 (1966).

Solid State Comm. ±, 625 (1966).

13. BOL’SHOVA K.M. and YELKINA T.A., 14. HOWLIN C.H. and JONES R.V.,

16. COOKE A.H., Phys. Rev. Left.

J. Appi. Phys. 37, 1320 (1966).

GORJAGA A. N. and SHRINTVASAN SI.,

15. ANDERSON E.E.,

Vol. 5, No.12

Phys. Rev.

Zh. Eksper. Teor. Fiz. 51, 1639 (1966).

Fiz. Tverd. Tela, 8, 2811 (1966).

J. Appl. Phys. 34,

1262 (1963).

134, A2581 (1964).

GEHRING K.A.,

LEASK M.J.M.,

SMITH D. and THORNLEY J.H.M.,

14, 685 (1965).

CWHT~3If~OB~HbIHOBbI~ npo~patnmie ~beppIIMarHWTHbIe MOHOKPHCT~JL7ThI

cocTaBa Rb(Ni!_xOox)F3,

r~ex II3M~H~~TC~ OT 0 ~o

0,3.

Rb*i33 CT0 =139°K)IiMeeT MaI’HHTHyIO ~HH3OT~0flJ4IO TI4U~“3IerK3~ tt, RbN1 fl1OCI~OCTL 070o03F3 (T0 _lo9oK) ~jiericas~oci”. 0~Hapy~iteRo,qTo Bd3II~3L~TOT.lIC~ Kiopa ~JIH o~oiccB~U~~CTB BLIIIO~IH~1OTCH3~KOHbI ~ ~d(T_T0)~”3H

~‘8_.(T0—T)O.~~