Structural and magnetic properties of Ce-Y substituted strontium nanohexaferrites

Abstract

Strontium nanohexaferrites substituted with Ce-Y were synthesized via citrate sol-gel combustion. Crystallography phase and morphology were verified by X-ray diffraction, electron microscope and Raman spectroscopy. The magnetization hysteresis loop (M vs. H) revealed the ferromagnetic behavior of all prepared products. The estimated saturation (M_s) and the remnant (M_r) magnetizations values are maximum for pristine SrY_0.5Ce_0.5Fe₁₁O₁₉ (i.e. x=0.5) and SrY_0.3Ce_0.3Fe_11.4O₁₉ (i.e. x = 0.3) due to both Y³⁺ and Ce³⁺ contents. The obtained squareness ratio (M_r/M_s) values for substituted products are less than the value of 0.500 suggesting the uniaxial anisotropy for all substituted products. The magneto-crystalline anisotropy fields (H_a) values are very large indicating the hard-ferromagnetic features of all elaborated nanoparticles samples. It is found that H_a decreased with increasing both Y³⁺ and Ce³⁺ contents and is minimum for x = 0.5, which imply the weakening of magnetic properties. Therefore, the coercive field (H_c) value is diminished due to Y³⁺ and Ce³⁺ substitutions and its minimum corresponds to x = 0.3. The blocking temperatures (T_B) are estimated from ZFC and FC magnetizations experiments. It is observed that T_B shifts to higher temperatures with rising Y³⁺ and Ce³⁺ contents. This is ascribed to the reduction of particles size with Y and Ce substitutions.

Introduction

Nowadays, nanomaterials have received much attention owing to their extensive applications [1], [2], [3], [4], [5]. Higher working frequencies communication and electronic systems, expansion of radar, anti-electromagnetic interference coating and microwave darkroom [6], [7] are attracted more attentions. Recently, this technology improvement has start out the potential of hard hexaferrites in ferrite devices and operates in microwave frequencies [8], [9], [10]. The benefit of hard M-type hexagonal ferrites come from strong uniaxial magneto-crystalline anisotropy and therefore high frequency of magnetic resonance, with an extreme registered value of 47.6 GHz for Barium hexaferrites oriented particles [11] and with range that permeability reaches needed higher value with lowest magnetic losses is enlarging to higher frequencies. The microwave absorbing abilities of M-type hexaferrites can be developed using some of rare earths metals as a substitution of Fe⁺³ and Sr⁺² cations in the main matrix [12]. Moreover, fabrication techniques with type and concentration of the substitutions play significant role in the properties of metal substituted ceramic magnets [13], [14], [15], [16]. Substitution using rare earths were acting as an inhibitor of grains growth [17], promote the ferritization reaction [18]. Furthermore, lanthanides enhance the mechanical materials hardness [19] and enhance the hard magnetic properties of Strontium hexaferrites [20]. The unique magnetic properties of Strontium hexaferrite would be affected by the partially substitution of Fe or Sr sites, or both. So, recent investigations have been reported about an important improvement in SrFe₁₂O₁₉ hexagonal ferrites by the replacement of Sr²⁺ sites by Gd³⁺ [21], Sm³⁺ [22], Nd³⁺ [23], La³⁺ ions [24], ions of Fe³⁺ by non-magnetic ions such as Cd³⁺ [25], Ga³⁺ [26], Zn³⁺ [27], and Al³⁺ [28] and magnetic ions such as Cr³⁺ [29] and Co²⁺ [30] ions and substitution of both Sr²⁺ and Fe³⁺ with La–Zn [31], La–Cu [32] and Pr–Zn [33].

The present work focuses on the co-substitution of divalent Ce³⁺ ion together with Y³⁺ ion on two trivalent Fe³⁺ ions in M-type strontium hexaferrite. To the extent of our knowledge, no study has been presented concerning SrY_xCe_xFe_12-xO₁₉ nanohexaferrites. Therefore, the effect of bimetallic substitution on the microstructure and magnetic properties of Sr-hexaferrite was investigated.