Magnetic resonance study of
nanocrystalline hematite-ilmenite
solid solutions
1,2 2 2 2 3
N. Guskos , G. Zolnierkiewicz , J. Typek , A. Guskos , and D. Petridis
1
Solid State Section, Department of Physics, University of Athens, Panepistimiopolis, 15 784 Zografos, Athens, Greece
2Institute of Physics, West Pomeranian University of Technology, Al. Piastow 48, 70-311 Szczecin, Poland
3NCSR „Demokritos“, Aghia Paraskevi, Attikis, Athens, Greece
Abstract
Nanocrystalline hematite-ilmenite (Fe O , FeTiO ) solid solutions containing small amounts of hematite have been prepared and 2 3 3
investigated by magnetic resonance technique in the 4-300 K temperature range. At room temperature the magnetic resonance
spectra have been fitted by two Lorentzian lines centered at H =325.3(1) mT (g =2.054(1)) and H =335.3(1) mT (g =2.015(1)) with r eff r eff
linewidth ÄH =83.0(1) mT and ÄH =54.0(1) mT, respectively. Temperature dependence of the resonance lines suggests that the pp pp
first line arises from the ferromagnetic agglomerates (ferromagnetic resonance, FMR) and the second line from isolated high spin
trivalent iron(III) ions (electron paramagnetic resonance, EPR). Below 100 K additional lines centered at 159.5(4) mT (g =4.236) eff
and 334.2(4) mT (g =2.007) has appeared. As their intensity increases with decreasing temperature a probable source of that signal eff
are the trivalent iron(III) ions placed at sites with a low symmetry of the crystal field. At room temperature the position of the
resonance line and the value of its linewidth is consistent with a small concentration of the Fe O in a non-magnetic matrix. The 2 3
temperature derivate of the resonance field ÄH /ÄT is over two times greater in comparison with other diamagnetic matrices. This r
points out on more intense reorientation processes of the magnetic moments in nanocrystalline hematite-ilmenite solid solutions
(Fe O , FeTiO ).2 3 3 1 0 0 0 2 0 0 0 3 0 0 0 4 0 0 0 5 0 0 0 - 8 0 0 0 - 6 0 0 0 - 4 0 0 0 - 2 0 0 0 0 2 0 0 0 4 0 0 0 6 0 0 0 d c "/d H [A rb .u ni ts ] T e m p e r a tu r e T [K ] 9 0 K 2 9 0 K DT = 2 0 K 1 0 0 0 2 0 0 0 3 0 0 0 4 0 0 0 5 0 0 0 - 3 0 0 0 0 - 2 0 0 0 0 - 1 0 0 0 0 0 1 0 0 0 0 2 0 0 0 0 3 0 0 0 0 4 0 0 0 0 1 0 0 0 2 0 0 0 3 0 0 0 4 0 0 0 5 0 0 0 - 3 0 0 0 0 - 2 0 0 0 0 - 1 0 0 0 0 0 1 0 0 0 0 2 0 0 0 0 3 0 0 0 0 4 0 0 0 0 d c ¨/d H [A rb .u ni ts ] M a g n e tic f i e l d H [ G s ] 5 0 K 5 K 2 9 0 K 2 0 K 1 8 0 K d c ¨/d H [A rb .u ni ts ] M a g n e t i c f i e l d H [ G s ] 8 5 K 5 K 6 K 7 K 8 K 1 0 K 1 2 K 1 5 K 1 7 K 100 150 200 250 2.0 2.1 2.2 2.3 2.4 2.5 g1 g2 g e ff X Axis Title 100 150 200 250 300 400 500 600 700 800 dH1 dH2 L in e w id th 1 /2 D H p p [G s ] Temperature T [K] 100 150 200 250 0.00E+000 3.00E+008 6.00E+008 9.00E+008 1.20E+009 1.50E+009 Iint1 Iint2 In te g ra te d in te n s it y I int [A rb . u n it s ] Temperature T [K] 5 0 1 0 0 1 5 0 2 0 0 2 5 0 2 2 0 0 2 4 0 0 2 6 0 0 2 8 0 0 3 0 0 0 3 2 0 0 R es on an ce fie ld H r [G s] T e m p e ra tu re T [K ] 1 0 0 0 2 0 0 0 3 0 0 0 4 0 0 0 5 0 0 0 -3 0 0 0 0 -2 0 0 0 0 -1 0 0 0 0 0 1 0 0 0 0 2 0 0 0 0 3 0 0 0 0 d c "/ dH [A rb .u ni ts ] M a g n e tic fie ld H [G s ] 0 1 0 2 0 3 0 4 0 5 0 0 5 0 0 0 1 0 0 0 0 1 5 0 0 0 2 0 0 0 0 2 5 0 0 0 3 0 0 0 0 A m pl itu de A pp [A rb .u ni ts ] T e m p e ra tu re T [K ]
Figure 1. Temperature dependence of the FMR spectra in high temperature (a) and low temperature ranges (b). Inset in (b) shows comparison of FMR spectra at very different temperatures.
Figure 2 Temperature dependence of the FMR parameters, (a) g , (b) linewidth ÄH and (b) integrated intensity Ieff pp itegr (c).
Figure 3 The temperature dependence of the average
resonance field. Figure 4 The fitting of magnetic resonance spectra at 5 K.
Figure 5 The temperature dependence of the amplitude of EPR spectra of iron ions.
a) b)
