Structural, magnetic and magnetocaloric properties of Mn2-xCrxSb compounds have been studied. In these compounds a first order magnetic phase transition from the ferrimagnetic to the antiferromagnetic state occurs with decreasing temperature, giving rise to giant inverse magnetocaloric effects that can be tuned over a wide temperature interval through changes in substitution concentration. Entropy changes as high as 7.5 J/kgK have been observed, and a composition independent entropy change is obtained for several different concentrations/working temperatures, making these compounds suitable candidates for a composite working material.

Tuning the giant inverse magnetocaloric effect in Mn2-xCrxSb compounds

Sol-gel synthesized double perovskite Gd2FeCrO6 nanoparticles: Structural, magnetic and optical properties

The strong coupling between 3d and 4f based magnetic sublattices in double perovskite (DP) compounds results in various exotic complex magnetic interactions, and the ground state contains multiple fascinating and remarkable magnetic states. In this article, we have performed a detailed investigation of the crystal structure, magnetic, and magnetocaloric properties of the ordered monoclinic polycrystalline double perovskite Ho 2 CoMnO 6 (HCMO) compound. A study of the magnetization dynamics employing temperature and magnetic field shows a powerful correlation between Ho and Co/Mn sublattices. Due to the presence of the ferromagnetic superexchange interaction in between Co 2 + − O − Mn 4 + networks, the system undergoes an ordered state at the transition temperature, T C ≈ 77 K. Below T C, a clear compensation point continued by negative magnetization is noticed in the virgin state of the compound. The reduction of the saturation magnetization ( M S) in the hysteresis curves (M-H) can be explained by the existence of local anti-site defects or disorders and anti-phase boundaries in the system. Temperature dependence of magnetic entropy change ( − Δ S) curves shows a maximum value of 13.4 J/kg K for Δ H = 70 kOe at a low temperature along with a noticeable inverse magnetocaloric effect. Moreover, the material holds reasonable values of magnetocaloric parameters. The absence of thermal hysteresis along with a large value of | Δ S | makes the system a potential candidate for low temperature as well as liquid nitrogen temperature-based magnetic refrigeration. Additionally, our experimental findings should encourage further detailed studies on the complex 3d–4f exchange interaction in the double perovskite system.

Role of 3d–4f exchange interaction and local anti-site defects in the magnetic and magnetocaloric properties of double perovskite Ho2CoMnO6 compound

In this work, new double perovskite Tb2ZnMnO6 nanoparticles were successfully synthesized by a sol–gel auto combustion method.

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Green sol–gel auto combustion synthesis and characterization of double perovskite Tb2ZnMnO6 nanoparticles and a brief study of photocatalytic activity

The effect of high temperature annealing on the antisite defects in ferromagnetic La2NiMnO6 double perovskite

Homogeneous solid solutions of sol–gel-prepared R2NiMnO6 (R = La, Pr, Nd, Sm, Gd, Tb, Dy, Y, and Ho) double perovskites crystallize in a B-site-ordered monoclinic structure (P21/n space group). Mon...

https://pubs.acs.org/doi/pdf/10.1021/acsaelm.8b00062

Role of Antisite Disorder, Rare-Earth Size, and Superexchange Angle on Band Gap, Curie Temperature, and Magnetization of R2NiMnO6 Double Perovskites

Influence of Cation Order and Valence States on Magnetic Ordering in La 2 Ni 1− x Mn 1+ x O 6

The double perovskite La2FeMnO6 is ideally expected to be a ferrimagnet with a low saturation moment of 1 μB/f.u. Inhomogeneity in the Fe/Mn sites, along with other lattice disorders, can modify the exchange interactions in the material and result in a net saturation moment of more than 1 μB/f.u. Here, the origin of complicated magnetic behavior is examined of a pure phase La2FeMnO6 sample prepared by the sol-gel method. XRD analysis established that the material crystallizes in the orthorhombic Pbnm symmetry. The comprehensive analysis of X-ray photoelectron spectroscopy, X-ray near edge structure, and magnetic measurements acknowledge an antiferromagnetic coupling between Fe3+ and Mn3+ cations; thereby, resulting in the ferrimagnetic ground state for La2FeMnO6. The magnetic hysteresis loop obtained at 5 K shows a large coercivity of ~740 Oe and a saturation moment of 1.6 μB/f.u., hinting at partial B-site ordering in La2FeMnO6. The ac susceptibility and dc magnetization measurements indicate the existence of magnetic glassy states (of cluster-glass type) with two distinct dynamical freezing points at ~27 and 92 K, along with a Griffiths-like phase in the material. The experimental results are discussed taking several possible exchange interactions among Fe3+ and Mn3+ ions in the system into consideration. The magnetic complexity of this system makes it attractive for fundamental research and technological applications.

Evidence of cluster-glass and Griffiths-like phases in partially ordered La 2 FeMnO 6 double perovskite

The structural, electronic, and magnetic properties of a sol-gel prepared series of La2Ni1−x Sc x MnO6 compounds have been extensively studied using x-ray diffraction, x-ray absorption near edge structure, and dc magnetization techniques, respectively. The entire series was isostructural and exhibited the La2NiMnO6 double perovskite P21/n monoclinic structure. The nonmagnetic Sc3+ substitution led to the evolution of competing magnetic phases in La2Ni1−x Sc x MnO6. The substitution also caused an increase in lattice parameters, cell volume, and bond lengths. Consequently, Sc3+ dilution resulted in a dramatic decrease in Curie temperature, suggesting a reduction in the strength of the Ni2+–O2−–Mn4+ superexchange ferromagnetic interaction. The Sc3+ substitution generated antisite defects, which significantly suppressed the saturation magnetization of the system. The competing magnetic interactions observed in the La2Ni1−x Sc x MnO6 system are discussed in terms of cation disorder, cation valances, and changes in the bond lengths/angles, caused by the Sc3+ substitution.

Subhash Bhatt

Papers

Role of Antisite Disorder, Rare-Earth Size, and Superexchange Angle on Band Gap, Curie Temperature, and Magnetization of R2NiMnO6 Double Perovskites

The effect of high temperature annealing on the antisite defects in ferromagnetic La2NiMnO6 double perovskite

Influence of Cation Order and Valence States on Magnetic Ordering in La 2 Ni 1− x Mn 1+ x O 6

Evidence of cluster-glass and Griffiths-like phases in partially ordered La 2 FeMnO 6 double perovskite

Unraveling the impact of nonmagnetic Sc substitution on the magnetic properties of La2NiMnO6 double perovskite