Magnetic resonance study of Fe2O3 -betaine-MnCl system

Magnetic

resonance

study of

g

-Fe O -betaine-MnCl

₂

₃

₄

system

1 1, 2 1 3

J. Typek , N. Guskos , G. ¯o³nierkiewicz , D. Petridis ,

1

K. Wardal

1

Institute of Physics, West Pomeranian University of Technology, Al. Piastow 48, 70-311 Szczecin, Poland

2

Solid State Section, Department of Physics, University of Athens Panepistimiopolis, 15 784 Zografos, Greece

3

Institute of Materials Science, NCRS “Demokritos” 153 10 Aghia Paraskevi, Attikis, Athens, Greece

A novel class of compounds combining molecular magnets with ferrimagnetic iron oxide nanoparticles was synthesized. The purpose was

to examine the effect of the magnetic properties of g -Fe O_{2 3}on the magnetic properties of its partner. In this report we describe the magnetic

2+ 2- +

-resonance behaviour of Mn bound as an MnCl an ion₄ to g -Fe O_{2 3}through a betaine (Me N - CHCOO ) spacer. Nanosize ₃ g -Fe O_{2 3}was

prepared according to the precipitation method using FeCl₃·6H O₂ and FeSO₄·7H O in₂ the 2:1 mole ratio. After isolation and washing the g

-Fe O_{2 3}nanoparticles were dispersed in water and treated with betaine. The solid g -Fe O_{2 3} -betaine was dispersed in ethanol containing a few

drops of HCl. MnCl₂was added to this solution. The obtained sample was investigated by using an X -band electron paramagnetic resonance

(Bruker E 500)spectrometer inthe90-300 Ktemperaturerange. Theregisteredspectraarepresented inFigure 1.

The temperature dependence of integrated intensity (calculated as an area under the absorption curve) displayed the Curie - Weiss - type of

behaviour, I(T)=C/(T - T ), with T = - 33.2 K. This indicates on the existence of strong antiferromagnetic interactions in the studied sample._{0 0}

The spectral lines were slightly asymmetric and they were attributed to the g- Fe O nanoparticles in a superparamagnetic state. Following _{2 3}

the method proposed by Kliava, the registered spectra were fitted by two lines with lineshapes obtained from the solution of the Landau -

Lifshitz equation. These two component lines were a result of magnetic anisotropy of the g-Fe O nanoparticles. As an example, a comparison of _{2 3}

the experimental and fitted spectra at T =120 K is presented in Figure 2. The fitting allowed to determine the intrinsic resonance fields, linewidths and integrated intensities of both spectral components at different temperatures. The two obtained resonance fields (280 and 345 mT) did not vary in the studied temperature range (Fig. 5). This behaviour was in contrast to the usually observed decrease in the resonance field with lowering temperature for typical nanoparticles embedded in a non - magnetic matrix. On the other hand, two linewidths showed a pronounced temperature variation (Figure 3). On lowering the temperature the linewidths increased significantly.

0 1 0 0 0 2 0 0 0 3 0 0 0 4 0 0 0 5 0 0 0 6 0 0 0 7 0 0 0 - 1 0 - 8 - 6 - 4 - 2 0 2 4 6 8 1 0 S ig na la m pl itu de [a .u .] M a g n e tic f ie ld [G ] 9 0 K 1 0 0 K 1 1 0 K 1 2 0 K 1 3 0 K 1 4 0 K 1 5 0 K 1 6 0 K 1 7 0 K 1 8 0 K 1 9 0 K 2 0 0 K 2 1 0 K 2 2 0 K 2 3 0 K 2 4 0 K 2 5 0 K 2 6 0 K 2 7 0 K 2 8 0 K 2 9 0 K 0 1 0 0 0 2 0 0 0 3 0 0 0 4 0 0 0 5 0 0 0 6 0 0 0 7 0 0 0 -8 -6 -4 -2 0 2 4 6 8 F M R si gn al am pl itu de [a .u .] M a g n e tic fie ld [G ] T = 1 2 0 K 100 150 200 250 300 2500 2600 2700 2800 2900 3000 3100 3200 3300 3400 3500 3600 3700 3800 3900 4000 R e s o n a n c e fi e ld [G ] Temperature [K] 100 150 200 250 300 800 900 1000 1100 1200 1300 1400 L in e w id th [G ] Temperature [K] 100 150 200 250 300 1.5 2.0 2.5 3.0 3.5 4.0 0.20 0.25 0.30 0.35 0.40 0.45 0.50 0.55 0.60 0.65 In te g ra te d in te n s it y [a .u .] Temperature [K] (I n te g a te d in te n s it y ) -1 [a .u .]

Figure 1: Magnetic resonance spectra of the investigated sample registered at different temperatures in the 90-300 K range.

Figure 2: Experimental (black) and fitted (red) spectra of the investigated sample at T= 120 K.

Figure 3: Temperature dependence of linewidths of two fitted components

Figure 5: Temperature dependence of the resonance field for two components of the FMR spectrum. Figure 4:Temperaturedependenceofintegratedintensity(leftaxis)

andreciprocalofintegrated intensity (rightaxis) forinvestigated sample