Morphology and magnetic traits of strontium nanohexaferrites: Effects of manganese/yttrium co-substitution

doi:10.1016/j.jre.2018.09.014

Journal of Rare Earths

Volume 37, Issue 7, July 2019, Pages 732-740

https://doi.org/10.1016/j.jre.2018.09.014 Get rights and content

Abstract

Doped strontium (Sr) hexaferrites appeared potential candidates for microwave absorber applications. Driven by this idea, we examined the influence of manganese (Mn) and yttrium (Y) co-substitution on the microstructures, morphology and magnetic properties of Sr nanohexaferrites (Sr_1–xMn_xFe_12–yY_yO₁₉, where 0.0 ≤ x = y ≤ 0.5) synthesized via citrate sol-gel auto-combustion technique. As-prepared samples were thoroughly characterized using diverse analytical tools. X-ray diffraction pattern reveals a single M-hexagonal crystalline phase. FE-SEM, TEM, HR-TEM show a hexagonal platelet-like structure. The magnetic hysteresis loops (measured at room and low temperature) of the as-prepared nanohexaferrites exhibit ferromagnetic (FM) behavior. Magnetic parameters including the saturation magnetization, remanence, coercive and magneto-crystalline anisotropy field are found to decrease with the increase in Mn²⁺ and Y³⁺ contents. Zero- and normal-field cooled magnetization measurements in the range of 2–400 K display the complete absence of blocking temperature, confirming the characteristic ferromagnetic behavior of the proposed composition.

Graphical abstract

The influence of manganese (Mn) and yttrium (Y) co-substitution on the microstructural, morphological and magnetic properties of strontium nanohexaferrites (Sr_1-xMn_xFe_12-yY_yO₁₉; 0.0 ≤ x = y ≤ 0.5) was examined. The magnetic hysteresis loops of the various produced nanohexaferrites indicate ferrimagnetic behavior.

Introduction

Lately, M-type strontium nanohexaferrites (SrFe₁₂O₁₉) being the hard-magnetic materials became greatly prospective for microwave integration technology.¹ Excellent microwave (MW) absorption capacity of M-type hexaferrites due to their large anisotropy field allows to reduce the electromagnetic backscattering as well as interference at higher microwave range.2, 3, 4 Meanwhile, Sr hexaferrites owing to their gifted magnetic traits have emerged as permanent magnets.³ Diverse researches revealed that the substitutions of Sr²⁺ and Fe³⁺ ions in Sr hexaferrites by non-magnetic and magnetic ions such as Co²⁺, Mn²⁺, Sn⁴⁺, Zr⁴⁺, Mg²⁺ as well as rare earth ions such as La³⁺, Ce³⁺, Sm³⁺, Y³⁺, Nd³⁺ and Dy³⁺ can affect significantly the magnetic attributes of Sr hexaferrites.5, 6, 7, 8, 9, 10, 11, 12, 13

Over the years, dedicated efforts have been made to control and improve the magnetic properties of Sr hexaferrites. Gordani et al.¹⁴ examined the magnetic behavior of Mg-Co-Ti substituted Sr hexaferrites at varied doping levels (ranged from 0.0 to 2.5). Results showed a remarkable reduction in the magnetization with increasing doping contents accompanied by more effective reflection loss compared to undoped Sr hexaferrites. Such disclosure indeed authenticated the usefulness of Sr hexaferrites for MW absorber applications. Kang et al.¹² prepared Ce and Mn co-substituted Sr hexaferrites (Sr_1–xCe_xFe_11–xMn_xO₁₉ and Sr_1–xCe_x Fe_11–2xMn_2xO₁₉ with varying x) via solid-state reaction route. The magneto-crystalline anisotropy of such hexaferrites was found to enhance with the increase in the substitution levels (values of x). Yang et al.¹⁵ inspected the magnetic characteristics of aluminum (Al) and lanthanum (La) co-substituted Ca (calcium) Sr hexaferrites with composition Ca_0.6Sr_0.1La_0.3Fe_12–xAl_xO₁₉ (where 0.0 ≤ x ≤ 1.4). The values of saturation magnetization (M_s) and coercive field (H_c) were augmented and remanence (M_r) was reduced with increasing Al to La ratio into the Ca-Sr hexaferrites. Despite some works an accurate method for the preparation of such hexaferrites with controllable magnetic attributes remain deficient. On top, correlation between microstructures and magnetic traits of co-substituted Sr hexaferrites is still to be clarified.

Considering the immense technological potential of Sr hexaferrites, we prepared Sr nanohexaferrites (NHFs) of chemical composition Sr_1–xMn_xFe_12–yY_yO₁₉ (where 0.0 ≤ x = y ≤ 0.5) with Mn/Y co-substitution (hereafter prepared samples are designated as MY-SNHFs). Such Sr nanohexaferrites were synthesized using citrate sol-gel auto-combustion technique and characterized. Effects of varied co-substitution levels (x and y) on the microstructures, morphology and magnetic properties of the proposed Sr nanohexaferrites were evaluated to determine the feasibility of achieving their improved microwave absorbing capacity. Results were analyzed, discussed, and compared with other recent findings.

Section snippets

Materials and methods

Analytical grade high purity (Sigma Aldrich (99.9%)) powders of Fe(NO₃)₃·9H₂O, Sr(NO₃)₂, Mn(NO₃)₂ and Y₂O₃ were used to prepare Sr nanohexaferrites by citrate sol-gel auto-combustion method. Sr hexaferrites of chemical composition Sr_1–xMn_xFe_12–yY_yO₁₉ (0.0 ≤ x = y ≤ 0.5) were achieved. First, appropriate amount of Fe(NO₃)₃·9H₂O, Sr(NO₃)₂ and Mn(NO₃)₂ were dissolved in deionized water before being heated at 80 °C under constant magnetic stirring. Next, yttrium oxide Y₂O₃ was dissolved in 10 mL of

Structural properties

Fig. 1 shows XRD patterns of synthesized Sr nanohexaferrites, which shows single phase hexagonal crystal structure matched with ICDD card number [96-100-8857]. The appearance of weak peaks for Srnanohexaferrites at higher substitution ions contents was allocated to the α-Fe₂O₃ phase. Table 1 enlists the calculated lattice parameters and average nanocrystallite size (D_XRD). Values of D_XRD at different substitution ions contents were estimated using Scherrer's formula, wherein the intense XRD

Conclusions

This study reported the effects of Mn and Y ions co-substitution on the microstructures, morphology and magnetic behaviors of M-type nanohexaferrites prepared using citrate sol-gel auto-combustion technique. XRD patterns of these nanohexaferrites show single M-hexagonal crystalline phase. The magnetic hysteresis loops of proposed nanohexaferrites at 300 and 10 K disclose ferromagnetic character. Overall magnetic characteristics is affected by the variation in the Mn²⁺ and Y³⁺ contents. Zero-

Acknowledgements

The authors highly acknowledged the Institute for Research & Medical Consultations (IRMC) of Imam Abdulrahman Bin Faisal University (IAU – Saudi Arabia) for supporting this study through the Projects application number: [2017-IRMC-S-3]; [2018-IRMC-S-1] and [2018-IRMC-S-2].

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Morphology and magnetic traits of strontium nanohexaferrites: Effects of manganese/yttrium co-substitution

Abstract

Graphical abstract

Introduction

Section snippets

Materials and methods

Structural properties

Conclusions

Acknowledgements

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