Morphology, structure and magnetic behavior of orthorhombic and hexagonal HoFeO3 synthesized via solution combustion approach

doi:10.1016/j.jre.2021.01.001

Journal of Rare Earths

Volume 40, Issue 2, February 2022, Pages 296-301

https://doi.org/10.1016/j.jre.2021.01.001 Get rights and content

Abstract

Nanostructured HoFeO₃ powders were obtained by solution combustion method at various glycine-nitrate ratios (G/N = 0.2, 0.4, …, 1.4). According to X-ray powder diffractometry data, the presence of two modifications of HoFeO₃ in the synthesized samples was established: orthorhombic (Pbnm) and hexagonal (P6₃/mmc). The crystallite size of the obtained compositions varies from 62 ± 6 to 29 ± 3 nm, depending on the G/N ratio. From magnetic structure studies, it is found that HoFeO₃ obtained with a stoichiometric amount of glycine in the reaction solution is in the magnetically ordered state and is represented by a sextet with quadrupole splitting (QS) = 0 mm/s, isomeric shift (IS) = 0.36 mm/s and effective field strength (H_eff) = 497 kOe. According to the results of vibrational magnetometry, it is found that the orthoferrites obtained have a ferromagnetic structure, the main parameters of which (M_s, M_r and H_c) systematically change with a change in the redox ratio of the reaction mixture and, as a consequence, their phase composition, and reach maximum values at a G/N ratio = 0.6. In the samples obtained with a significant excess and lack of glycine (G/N = 0.2 and 1.4), despite their amorphous nature, hysteresis loops characteristic of the ferromagnetic state of the substance is observed. It is hopeful to obtain a pure hexagonal modification of HoFeO₃ via heat treatment on amorphous products of glycine-nitrate combustion.

Graphical abstract

The procedure aimed at synthesis of hexagonal metastable HoFeO₃ nanocrystals by solution combustion method was elaborated. It is found that the glycine-nitrate ratio makes it possible to obtain holmium ferrite with structural and magnetic parameters in a wide range of values.

Introduction

Over the past decades ferrites and orthoferrites of rare-earth elements (RFeO₃) remained relevant research objects due to the practical importance of these materials both for science and for modern industry.1, 2, 3, 4 The interest in functional materials based on them is associated with the possibility of obtaining compositions with controlled electromagnetic properties in a wide range of parameters suitable for use in the manufacture of high-frequency devices,5, 6, 7 sensors,⁸^,⁹ magnetic storage media,¹⁰ magnetic fluids,¹¹ etc. Besides, rare-earth orthoferrites with weak antiferromagnetism together with several fundamental physical properties such as spin reorientation transitions at 80–480 K,¹² the para-to antiferromagnetic transitions at 620–750 K,¹³ and multiferroicity¹⁴^,¹⁵ have found their application in the production of spintronic devices. In addition to the well-studied usage of ferrites and orthoferrites in the industrial production of radio equipment, an increasing number of researchers pay attention to the possibility of using rare-earth orthoferrites of various compositions as catalytic materials that can be controlled by an external magnetic field to separate the wasted catalyst from the reaction mass, which significantly increases the efficiency of their use.16, 17, 18

Special attention is currently drawn to holmium orthoferrite (HoFeO₃), which also belongs to the class of perovskites and has a distorted ABO₃ orthorhombic structure of YFeO₃ type.¹⁹ The magnetic and dielectric nature of HoFeO₃ behavior, caused by a high degree of symmetry of its structure, has opened up the possibility of widespread use of this compound both in habitual fields of industrial use and in some unique ones, for example, as magnetotherapy products for the effective removal of acute and chronic pain in various injuries and fractures.²⁰ Moreover, various types of composite ceramics with the addition of HoFeO₃ as a dopant have been widely studied.²¹ It is known²² that the functional properties of these materials largely depend on the phase composition, structural features and size, as well as the shape and morphology of the nanocrystals obtained. However, despite the large number of currently known methods for producing nanostructured ferrites and orthoferrites, such as mechanochemical,²³ sonochemical,²⁴ hydrothermal,²⁵ sol–gel²⁶ and a number of other syntheses, high-tech equipment and a significant number of synthesis parameters should be implemented to obtain nanocrystals with desired functional properties.²⁷ In addition, a number of works are known where various methods were used to obtain hexagonal orthoferrites powders of various compositions.28, 29, 30 In contrast to the approaches listed above, the glycine-nitrate combustion method allows acquiring a resulting powder within several minutes with high phase uniformity of the final product and does not require the use of complex and expensive equipment.³¹^,³² An important advantage of the solution combustion synthesis (SCS) in the production of rare-earth orthoferrites is the ability to obtain not only a orthorhombic modification but also a metastable hexagonal form. Previously, the authors obtained by SCS a number of hexagonal orthoferrite nanopowders that were formerly synthesized exclusively on thin films.³³^,³⁴ However, detailed studies establishing the relationship of glycine-nitrate combustion conditions with phase and chemical composition, morphology, structural and magnetic features of hexagonal and orthorhombic HoFeO₃ have not yet been carried out, despite the industrial interest to this method for the production of functional materials.

Therefore, in this work, studies of these issues were conducted, namely, the formation patterns of HoFeO₃ both orthorhombic and hexagonal modifications under various conditions of solution combustion and the features of their magnetic structure. A comprehensive physicochemical analysis of all the samples was carried out, including investigation of the chemical and phase composition, morphological structure, crystal and magnetic structure, surface and magnetic characteristics. Based on the results obtained, the optimal parameters of glycine-nitrate ratios for obtaining the pure nanocrystalline phase of ortho o-HoFeO₃ and metastable hexagonal modification were determined.

Section snippets

Experimental

Samples of nanostructured HoFeO₃ were obtained by glycine-nitrate combustion method at various ratios of glycine to nitrates of the corresponding metals (G/N = 0.2–1.4). Corresponding step of increasing glycine-nitrate ratio (0.2, 0.4, …, 1.4) was chosen to take into account the possible formation of several phases of HoFeO₃, depending on various initial parameters of the reaction solution and previous works of the authors.²^,¹⁸ This ratio was calculated using the following equation: $G/N = \frac{n_{gly}}{n_{{NO}_{3}}^{'}}$

Elemental analysis and morphology

The elemental composition and morphology of the obtained compositions were studied by scanning electron microscopy and X-ray spectral microanalysis (Fig. 1). The data obtained indicate that all synthesized samples correspond (in composition) to stoichiometric HoFeO₃ within the error of the determination method used. Slight deviations from the composition are observed primarily in samples synthesized with significant excesses and deficiencies of glycine, which is associated with a specific mode

Conclusions

HoFeO₃ nanostructured powders were obtained by the solution combustion method at various glycine-nitrate ratios. The synthesized HoFeO₃ nanocrystals correspond to the orthorhombic and hexagonal modifications. All obtained samples of HoFeO₃ have a ferromagnetic structure and high magnetic parameters, which are tunable by varying the initial glycine-nitrate ratio. At a ratio of G/N = 1.2, under corresponding conditions, it is possible to obtain a metastable hexagonal modification of HoFeO₃ with a

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Morphology, structure and magnetic behavior of orthorhombic and hexagonal HoFeO3 synthesized via solution combustion approach

Abstract

Graphical abstract

Introduction

Section snippets

Experimental

Elemental analysis and morphology

Conclusions

J Clean Prod

J Rare Earths

J Alloys Compd

J Rare Earths

Ceram Int

J Magn Magn Mater

J Rare Earths

Adv Powder Technol

Ceram Int

J Mol Struct

J Magn Magn Mater

Mater Sci Eng B

Synthesis of nanocrystalline HoFeO3 photocatalyst via heat treatment of products of glycine-nitrate combustion

Russ J Gen Chem

Review on magnetic nanoferrites and their composites as alternatives in waste water treatment: synthesis, modifications and applications

Environ Sci: Water Res & Technol.

Low coercivity microwave ceramics based on LiZnMn ferrite synthesized via glycine-nitrate combustion

Nanosystems: Phys, Chem, Math.

Nickel substituted cadmium ferrite as room temperature operable humidity sensor

Sens Actuators, A

Magnetic properties of nanocrystalline Co-Ni ferrites

J Mater Sci

Synthesis and properties of magnetic fluids produced on the basis of magnetite particles

Russ J Appl Chem

Tailoring the magnetic and magnetoelectic properties of rare earth orthoferrites for room temperature applications

RSC Adv

Spectral dependence of photoinduced spin precession in DyFeO3

Phys Rev B

Controllable synthesis of pure-phase rare-earth orthoferrites hollow spheres with a porous shell and their catalytic performance for CO + NO reaction

Chem Mater

Morphology, structure and magnetic behavior of orthorhombic and hexagonal HoFeO₃ synthesized via solution combustion approach

Synthesis of nanocrystalline HoFeO₃ photocatalyst via heat treatment of products of glycine-nitrate combustion

Spectral dependence of photoinduced spin precession in DyFeO₃