MÖSSBAUER EFFECT AND MAGNETIC PROPERTIES OF AN AMORPHOUS Fe₂O₃

Abstract

RbumB. -Un oxyde amorphe de fer 011) a et6 prkpark par dkcomposition thermique d'un akrosol sur un substrat chauffk. Les mesures de la susceptibilitk magnktique montrent une temp&rature de N k l de 80 K. En dessous de 50 K on observe un moment thermo-remanent. Le moment paramagnetique est de 2,5 p~ par ion de fer, indiquant la prksence d'aggrkgats antiferromagnktiques. Les spectres Mijssbauer montrent un doublet paramagnetique au-dessus de 80 K avec un dkplacement isomerique de + 0,15 mmls. En dessous de 80 K une separation hyperfine est observke avec, ?L 5 K, Hhr = 470 kOe et AEQ = 0,11 mmls. 11 en est d6duit que les ions Fe3+ sont entourks par un octakdre dkforrne d'ions W-. Leurs axes de symktrie sont orient& arbitrairement dans la maille apkriodique, laissant une large dispersion des angles v entre Hhn et Vzz.

Magnetism of amorphous Fe 2 O 3 nanopowders synthesized by solid‐state reactions

“…2) reveal a slightly broadened doublet of the non-Lorentzian shape indicating a quadrupole splitting distribution which arises from the electric field gradient distribution encountered in amorphous iron(III) oxides [6,8,15]. The widths of the spectral lines (Γ 1/2 = 0.52 mm/s, both in S250 and in W250 samples) reflect the narrower distribution of the electric field gradients than in other amorphous Fe 2 O 3 powders (Γ 1/2 = 0.60-0.70 mm/s) [7][8][9]12]. The same isomer shift value for both samples, δ = 0.33 mm/s, corresponds to highspin Fe 3+ in octahedral coordination.…”

“…The superparamagnetic blocking temperature (T B ) of about 80 K was found by Prozorov et al for amorphous nanopowder prepared by sonochemical method from Fe(CO) 5 . The magnetic behaviour of amorphous Fe 2 O 3 thin films has been interpreted as paramagnetic with the antiferromagnetic ordering below the Neel temperature, which is mentioned to be about 80-100 K [6][7][8][10][11]. This interpretation is based mainly on the magnetic susceptibility measurements revealing negative paramagnetic Curie temperature between -95 and -200 K, depending on the synthetic route and reduced effective paramagnetic moment (2.5-5µ B ) explained by the local clustering of spins [6][7][8] or by the mixing of various spin states [11].…”

“…The magnetic behaviour of amorphous Fe 2 O 3 thin films has been interpreted as paramagnetic with the antiferromagnetic ordering below the Neel temperature, which is mentioned to be about 80-100 K [6][7][8][10][11]. This interpretation is based mainly on the magnetic susceptibility measurements revealing negative paramagnetic Curie temperature between -95 and -200 K, depending on the synthetic route and reduced effective paramagnetic moment (2.5-5µ B ) explained by the local clustering of spins [6][7][8] or by the mixing of various spin states [11]. The complex study of magnetic properties of amorphous Fe 2 O 3 powder (∼3 nm) in applied field [2] led to the evidence of four magnetic regimes: pure paramagnetic at T>110 K at low applied field, field induced spin clusters (superparamagnetic like) at higher applied fields at the same temperatures, interacting spin clusters with progressive freezing over 35 to 110 K and collective freezing below 35 K. With increasing applied field, the freezing temperature of spin-clusters decreases.…”

Magnetic and structural properties of iron-based oxide glasses, Fe 2O3-BaO-B2O3, from 57Fe Mössbauer spectroscopy

“…Considerable work has indeed been devoted recently to amorphous insulators [1][2][3][4][5][6][7][8]. Simple ionic compounds are generally difficult to obtain in the amorphous state [9,10]. Extensive literature exists on binary or ternary oxides, which are easier to prepare but usually cannot be compared to corresponding crystalline systems.…”

“…b) The peculiar magnetic transitions and orderings occurring in such glasses are a consequence of frustration connected with topological disorder [5][6][7][8][9][10]. Speromagnetism has been demonstrated in a few insulating amorphous materials and mictomagnetism or spin glass transitions have been characterized in a variety of concentrated oxide glasses [5-7, 15, 16].…”