Magnetization of magnetically inhomogeneous Sr2FeMoO6-δ nanoparticles

Gunnar Suchaneck

doi:10.3897/j.moem.7.3.75786

Abstract

Magnetization is a key property of magnetic materials. Nevertheless, a satisfactory, analytical description of the temperature dependence of magnetization in double perovskites such as strontium ferromolybdate is still missing. In this work, we develop, for the very first time, a model of the magnetization of nanosized, magnetically inhomogeneous Sr2FeMoO6-δ nanoparticles. The temperature dependence of magnetization was approximated by an equation consisting of a Bloch-law spin wave term, a higher order spin wave correction, both taking into account the temperature dependence of the spin-wave stiffness, and a superparamagnetic term including the Langevin function. In the limit of pure ferromagnetic behavior, the model is applicable also to SFMO ceramics. In the vicinity of the Curie temperature (T/TC &gt; 0.85), the model fails.

Highlights

Strontium ferromolybdate (Sr2FeMoO6-δ – SFMO) is the most studied ferrimagnetic double perovskite
The Curie temperature was fixed to TC = 420 K, the saturated magnetization to Ms = 3.75 μB/f.u., the the Landé spitting factor g to g ≈ 2, the low temperature spin-wave stiffness constant to D(0) = 1.4 ⋅ 10–21 eVm2, the range of exchange interaction to 〈r2〉 = a2, the magnetic flux density to B = 10 mT, and the effective magnetic moment of the superparamagnetic phase to μeff = 3 ⋅ 104 μB
Figure 2 illustrates the fractional change of magnetization ∆M/Ms of ferromagnetic SFMO induced by the spinwave T3/2 and T5/2 terms of Eq (8)

Summary

Introduction

Strontium ferromolybdate (Sr2FeMoO6-δ – SFMO) is the most studied ferrimagnetic double perovskite. SFMO double perovskites are promising candidates for magnetic electrode materials for room-temperature spintronics applications, because they present a half-metallic character (with theoretically 100% polarization), a high Curie temperature (TC) of about 415 K (ferromagnets should be operated in their ordered magnetic state below TC), and a low-field magnetoresistance [1]. The element first takes a single-domain state while in an ensemble of nanoparticles a superparamagnetic state appears at smaller sizes in dependence on temperature and observation (measurement) time. In the latter state, demagnetization occurs without coercivity since it is caused by thermal energy and not by the application of a magnetic field. The memory of the remanent state of the element is lost [2]

Methods

Results

Conclusion