IEEE TRANSACTIONS ON MAGNETICS, VOL. MAG-20, NO. 5 , SEPTEMBER 1984 1255

MEASUREMENT OF MAGNETIC PARAMETERS OF BUBBLE FILMS BY FERRIMAGNETIC RESONANCE AND FERRIMAGNETIC ANTIRESONANCE

J . Baszydski

Abstract - Ferrimagnetic resonance and f e r r i - magnetic antiresonance are used to measure t h e magnetic parameters ( magnetization, perpen- dicular uniaxial anisotropy, magnetocrystal- l ine anisotropy and g-factor 1 character iz ing the bubble material MnCr-ferrite.

INTRODUCTION

The magnetic f i e l d dependence of the R.F. magnetic susceptibil i ty possesses two fea tures o f i n t e r e s t f o r a given frequency. The suscep- t i b i l i t y o r , equivalently, the R.F. permeabil- i t y can be used to determine the magnetic parameters of magnetic materials.

near an appl ied f ie ld which corresponds t o a m a x i m u m i n t h e R.F, permeability. This is the well-known ferrimagnetic resonance effect - FMR. There is a second f i e l d wherf3 t h e r e a l par t of the R.P. permeability, zero and p" is very mall. T h P s f i e l d ' cor- responds to t he f e r r imagne t i c p t i r e sonance e f f e c t . - FMAR.

on FMAR in metal l ic mater ia ls possessing a l a rge e l ec t r i ca l conduc t iv i ty L 1 3 and amor- phous metal l ic glasses C 21 were publ ished in recent years. The first time that FMAR i n non- conducting materials was reported was on Y I G epi layers by Dewar e t a1 I 3 J. I n $his paper FMAR is descr ibed in semicon uc t i mater ia l s : ep i l aye r s o f f e r r i t e s (9 7 1 0 3 ~ cmY

Chan and Frai tova C4-J suggested the macroscopic theory of FMAR i n weakly conduct- ing ferrimagnetic materials. The nature of the FMAR ef fec t in insu la t ing fe r r imagnet ic mate- rials i s d i f fe ren t from that in me ta l l i c f e r - romagnets where the skin-effect plays an es- s e n t i a l r o l e . The spinwave roots change very l i t t l e in the FMAR region and the spin waves a re no t s ens i t i ve t o t he FMAR ef fec t . In the FMAR region one observes only the act ivi ty of the electromagnetic wave in the an t i resonance e f f e c t [4).

Insulating ferrimagnetic materials are essent ia l ly t ransparent t o microwave radia- t ion except a t ?DB where the transmission amplitude is heavily attenuated due t o the large absorption by the precessing magnetiaa- t ion. ?he transparency of the insulating fer- r imagnetic layers near FMAR increases. The po- s i t i o n of the FMAR peak in f i e ld g ives t he same s o r t of information about the magnetiza- t ion, g-factor, and anisotropy energies as does the position of the FMR peak.

Most invest igat ions have beeqcar r ied ou t

Many experimental and theoret ical papers

Manuscript received March 2, 1984 The author acknowledges support from the

I n s t i t u t e of Physics, Polish Academy of Sc iences , for th i s work.

cular Physics, Polish Academy of Sciences, Smoluchowskiego 17/19, 60-179 Pozna6, Poland

S. Baszyriski i s with t h e I n s t i t u t e o f Mole-

EXPERIMENTAL DETAILS

The specimens used i n this work were monocrystal l ine epi layers of ferr i tes , ob- ta ined by CVD method using the " small d is - tance technique [SI. A s t o t he subs t r a t e , we had access to f resh ly l i n e MgO s l i c e s w i t h {IO0 The laue- grams confirm that the ep c rys ta l l ine , with the j l O O j planes para l le l to the cleavage planes of MgO. I n t h e demag- n e t i z e d s t a t e a typ ica l s t r fpe s t ruc tu re of 2 r i c e p i l a y e r .

period was observed f o r the MnCr-fer-

I direct ion of the microwave power transmission

MELF 0.008 mm

0.6 mm

Fig. 1 The section through the specimen of the rectangular paral le lepiped f o r m o f the s i e e 12 x - 7 x ( 0.008 + 0.6 )m3 . (not scale 1.

A t the microwave frequency of 18.75 GBs, the magnetic properties of Mn- and mCr-fer- r i t e epi layers , 8 /urn thick, have been inves- t i ga t ed u s i t he microwave transmission technique ~3 . The epi layer were mounted over the open end o f a waveguide with a holding plate. A second waveguide, ax ia l ly ro t a t ed about 90' t o first, was attached t o the o ther side of the holding plate. The two waveguides fun'ctioned as two crossed polarizers with the f e r r i t e e p i l a y e r between them, A s t a t i c mag- n e t i c f i e l d , H, was maintained normal o r par- a l l e l t o t h e p l a n e o f the sample. The trans- mission was monitored by a diode detector. The-FMR and PMAR spec t ra were detected as the first der ivat ive of the t ransmission s ignal using a 400 Hz modulation of the magnetic f i e l d . A l l PMR and FMAR measurements were made at room temperature.

RESULTS AND DISCUSSION

The condi t ions for FMR and FMAR are: 1 . H applied perpendicular to the epilayer

plane, {lo01 :

2. N applied in the ep i layer p lane : a/ H p a r a l l e l t o t h e 4100 > di rec t ion

OO18-9464/84/0900-1255$01.00O1984 IEEE

1256

t (.)/-6) = ( HPMR + Hk ) ( Hm + 4mef + ‘k) ( 3, “ 1

dH b/ H p a r a l l e l t o t h e < 110 > di rec t ion

2 ‘k FMAR (Wd = (BpMB + -2 ) (Hw + 477Mef - HJ (4)

I n equations (1 ) t o ( 4 ) U is the angular fre- -k quency of the R.P. radiat ion; T i s the spec- t ro scop ic sp l i t t i ng f ac to r ; M is the magnet- iza t ion ; H is the uniaxial anisotropy f ie ld induced by‘growth condi t ions and/or s t ress i n the layer ; Hk i s the f i r s t -order cubic magneto- c rys ta l l ine an iso t ropy f ie ld ; HWR and Hm are the resonance magnet ic f ie lds for PMAR and FMR, respectively.

Fig. 2 and Fig. 3 . I I - H l k O e l

x 15

Typical resonance spectra are shown i n 5.64 fO.25

\

Fig. 2 F i r s t de r iva t ive , dP/dH, of t h e micro- wave power transmitted through a MnCr-ferrite monocrystalline epilayer f o r the magnetic f ie ld appl ied in the epi layer plane. 1 - H p a r a l l e l t o the <110) direction. 2 - H p a r a l l e l t o t h e ( l o o } direction. The microwave frequency w a s 18.75 GHz.

Fig, 3 Fi r s t de r iva t ive , dP/dH,of the micro- wave power transmitted through a MnCr-ferrite monocrystalline epilayer versus magnetic field, H , perpendicular to the sample. The FMAR and FMR peaks are labelled. The microwave f re - quency was 18.70 GHz.

The magnetic parameters characterizing the Mn- and MnCr-ferrite epilayers were deter- mined from the above data of FMR and FMAR ef- fects with self-consistent procedure. These parameters are shown i n Table 1.

From equations (1 1 and ( 2 ) we see tha t

477N = Hm - HFMAR

for the perpendicular geometry and, therefore , the measurement o f both FMR and FMAR i s a new method of determining the magnetization of

as grown semiconducting ferrimagnetic layers .

Table 1

The magnetic parameters characterizing the ferri te epilayers

Sample 4fiMef = MM - Q 4nM Hu Hk g-f ac t o r / FMR / / FMR and FMAR /

- MnFe204 6 870 4 950 - 1 920 - 205 2.004

[ MnCrFe) 3 200 4 680 1 480 - 410 2.015 2 20 f 10 2 10 f: 10 f 0.005

Results of measurements 4nMef, 4vM, Hu and Hk i n Oe

REPERENCES

see paper 1.27 t o 1281 c i t e d i n 141. Z. F r a i t , J. Magn. Magn. Mat., (1 983) 37 and the papers ci ted therein. G. Dewar; e R. K. Murthy M. Shone and R . Belt , J. Appl. Phys., & (1982) 2101-

r41

l51’

N. Chan and D. Praitova, Czech. J. Phys., E (1982) 1288. J. Baszyriski, 2nd Conference on (I Advances i n Magnetic Materials and their Applicat ions It, IBE Conf. Public. No. 142, 1, London 1976.