ANTIFERROMAGNETIC RESONANCE IN ORTHORHOMBIC WEAK FERROMAGNET YCrO3

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ANTIFERROMAGNETIC RESONANCE IN

ORTHORHOMBIC WEAK FERROMAGNET YCrO3

V. Sanina, E. Golovenchits, T. Fomina, A. Gurevich

To cite this version:

V. Sanina, E. Golovenchits, T. Fomina, A. Gurevich. ANTIFERROMAGNETIC RESONANCE IN

ORTHORHOMBIC WEAK FERROMAGNET YCrO3. Journal de Physique Colloques, 1971, 32

(C1), pp.C1-1149-C1-1150. �10.1051/jphyscol:19711411�. �jpa-00214453�

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JOURNAL DE PHYSIQUE

Colloque C I, supplPment au no 2-3, Tome 32, FGvrier-Mars 1971, page C 1 - 1149

ANTIFERROMAGNETIC RESONANCE

IN ORTHORHOMBIC WEAK FERROMAGNET YCrO,

V. A. SANINA, E.

1.

GOLOVENCHITS, T. A. FOMINA, A. G. GUREVICH Institute for Semiconductors, Academy of Sciences USSR, &ningrad, USSR

Rbum6. -

On a Ctudik la resonance antiferromagnetique dans des monocristaux de YCrO3 avec des champs pulsks et dans la gamme de longueur d'onde

1-6

mm. La dependance en champ de la frequence a et6 mesurQ avec un champ

Ho

dirige selon les axes a et c.

Pour

parallkle A I'axe a, le basculement des spins se produit pour

33

kOe. On calcule les paramhtres de I'knergie libre comme dans NaNiF3 qui avait ete prCddemment Ctudi6 et on en fait la comparaison.

Abstract.

- Antiferromagnetic resonance in YCr03 single crystals was studied in pulse magnetic fields in 1-6'mm wave-length range. The frequency vs field dependences were measured with magnetic field

Ho

directed along a and c axes.

For the HO directed along the a-axis at

H O = 33

kOe the spin-flop takes place. As in the earlier investigated orthorhombic NaNiF3 the parameters of the

free

energy were calculated. The obtained values of the parameters are compared with the values of the same parameters for NaNiF,.

According to [I] YCrO, has the perovskite structure change of the spectrum originated in the spin-flop with orthorhombic distortions (space group

'3::).

occures at Ho

=

Hr (33 * ^{3) kOe-}

Below the NCel temperature T,

=

141 OK this crystal We suppose that ail the AFMR signals we have is antiferromagnetical]y ordered with weak sponta- seen correspond t o the excitation of transverse AEMR neous moment directed along the

c

axis (Gx-type

magnetic structure).

Assuming the two-sublattice model the magnetic free energy of such crystal may be written in the form

:

where I , , , are the mechanical moments of the sublattices, connected with the magnetic moments M I

,,

by the expressions

:

The magneto-mechanical ratio tensors in this case have the form [2]

The plus and minus signs in eq. (3) correspond to y , and

y,

accordingly. In order to determine the values of parameters in eq. (1) and (3) we have measured the AFMR field vs frequency dependences for YCrO, single crystals.

The measurements were performed in the wave- length range 1-6 mm. Pulse magnetic fields up to 150 kOe were used. The magnetic field was directed along all three main axes of the crystal. But with magnetic field along the

<c

b

⁾⁾

axis no AFMR signals were found. The AFMR frequency vs field depen- dences (AFMR spectra) for two other orientations of the magnetic field Ho are shown in figure 1. One can see from this figure, that in the case H,

/ / a

asharp

Y l . 2 =

2l

^, ^O

⁰ⁱ

^ee:,^/,

^,

^Ho

^,

^koe

^,

80 Y x x 0 * Y X Z

0

YY,

0

+ Y Z X 0

Y u

FIG. 1. -

Resonance frequencies vs magnetic field for

YCrO,

at

77 OK.

Open circles

and full

circles correspond to

Ho

11

a

and

Ho

11

c

accordingly.

modes - with the frequencies o,,(H,//c) and oz,(Ho // a). The experimental dependences of these frequencies on Ho can be approximated by polyno- minals

:

The values of the coefficients in eq. (4) calculated by least squares method are

:

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:19711411

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C 1 -1150 V. A. SANINA, E. I. GOLOVENCHlTS, T. A. FOMINA, A. G . GUREVICH

a,,

=

(2.36 -1.

0.07)

x ~ O ' ~ ( M C ) ~ , Ax-,

=

(Ex, + 2 Ax,) - (E,, + 2 A , ) ,

Solid lines in figure 1 are the curves calculated using eq. (4) with the values (5) of the coefficients.

According to [3] the

oZ

vs Ho dependencies for transverse AFMR modes have the following form

:

+

^y,,(D

^-

^{S A}

^- ^2Ez1)IoH0 + & H Z , ,

where

7 x 2

'El =

- , z 2 = Y Z X .

Yxx Y z z

The frequencies (6) were calculated by solving equa- tions of motion in the form

The free energy expression

(1)

and eq. (7) have been written with suggestion

I:,,

=

const. (8)

This condition generally speaking is not correct if anisotropy of g-factors takes place. However, for such ions as Ni2+, Cr3+ or

V2+

the orbital angular moments in ground state are quenched, and a small addition of orbital moments to spin ones appears only because of the admixture ofexcited states:in second order of perturbation theory. In such case the condition (8) is approximately valid.

Using eq. (4) and (6) together with expressions for the spin-flop field H, and the spontaneous moment (see Ref. [4]), we have obtained the parameters in eq. (1) and (3). The values of these parameters are listed in Table I.

TABLE I

The values of effective$elds and g-factor components for YCrO,

DIo Ale EzI,

H D

=

- H A

=

-

H , =

-

⁼^Ax-z

-

^{1 0} ^gxx

^r

^~ ^Z⁼^Z ^g ⁷¹⁼^{7 2}⁼^T

Y

Y Y

Y

On can see from this table that in the case of YCrO,, as well as in the case of isomorphis crystal NaNiF, investigated previously [3], it is necessary to take into account all three origins of weak moment. These origins are the anisotropic exchange interactions (effec- tive field HD), the one-ion anisotropic interactions (effective field HA) and the off-diagonal components

(gz)

of the g-factor tensors. But as in the case of NaNiF, the largest contribution is that of the aniso- tropic exchange effective field. According t o Moriya

[5]

the following estimates for the effective fields HD and HA must be valid

( H ~ H , = ( $ ) ~ H ~ . , (9)

The experimental values of these effective fields for YCrO, as well as for earlier investigated isomorphic NaNiF, are listed in the table 11. One can see from this table that the experimental values for both crystals correspond rather well with the theoretical estimates.

The values of parameters for YCrO, and NaNiF, crystals

AgIg HDIHe (Ag/gI2 HAIHE

- -

YCrO,

0.03 0.05 0.001 0.002

NaNiF,

0.07 0.08

0.005

0.006

References

[I]

BERTAUT (E.

F.),

et al.,

Proceedings

of the International

[3]

GOLOVENCHITS

(E. J.),

SANINA

(V.

A,),

GUREVICH

Conference on Magnetism, Nottingam,

1964,

(A. G.),

Fiz. Tverd. Tela. 1969, 11, 642.

p. 275,

London,

1965. [4]

J u ~ m (V. M.), SHERMAN

( A . B.), Solid

State

Comm.,

121

TUROV

(E. A.). Phvsical Promrties of Mameticallv

1966. 4. 771.

- -

ordered crystals Ac. g i . USSR ~ u b c ~ o u s 6 ,

^[5]

MORIYA

^(T.),'

Weak ferromagnetisrn, in Magnetism,

Moskow,

1963. Ed. T.

Rado and

H.

Suhl, Acad. Press.,

1963.