Stoichiometric LaMnO3 has an orthorhombic crystal structure with an antiferromagnetic (TN ~ 140 K) insulating nature (1). The substitution of aliovalent cations (Sr2+ or Na1+) induce holes in the partially filled 3d shell of Mn and oxidizes the Mn3+ (t2g3eg1) to Mn4+ (t2g3eg0) and transforms the LaMnO3 to ferromagnetic metal through the double exchange coupling of Mn4+-O-Mn3+ (2). Since the Na1+ (1.39 Å) has an ionic radii closer to La3+ (1.36 Å) this would induce a twice number of holes compared to Sr2+ substitution. Drastic variations in their physical properties have also been found in different synthesis methods (3,4). Therefore, in this work, we adopted a recently emerging microwave (MW) heating to synthesise La1-xNaxMnO3 (x = 0, 0.1, 0.3) from the oxide precursors. Conduction or dielectric loss heating by MW irradiation enables the fast and homogenous reaction in few minutes. We achieved 1000 oC in 10 min and dwelled the samples for 20 min. The operating MW power alone was varied from 1000 W to 1200 W and 1400 W for x = 0.3 to examine the effect of MW power on its physical properties. Temperature-dependent magnetization and resistivity of x = 0, 0.1, 0.3 with fixed MW power (1200 W) are shown in Fig. 1 (a)&(b). A broad Curie transition is observed for undoped LaMnO3 with TC of 200 K, unlike our previous report on solid-state prepared La1-xNaxMnO3 where we observed TN = 140 K for undoped LaMnO3 (5), and the transition becomes narrow with increased TC as x increases. Insulating LaMnO3 transforms to metallic below TC upon Na doping. TC is denoted in the figure by dotted vertical lines. As the MW power increases from 1000 W to 1200 W, the resistivity of x = 0.3 decreases drastically and the metal-insulator transition also becomes sharp at a temperature very close to TC (Fig. 1(c)). The obtained microwave absorption peaks at a specific field show only a little increase with increasing the frequency of the MW signal. These findings will be correlated and discussed with the structural and morphological features acquired by microwave irradiation. 

**References:** 
(1) T. Tokura, et al., Mater. Sci. Eng. B 31(1-2), 187–191 (1995). 
(2) G.H. Rao, et al., J. Phys. Condens. Matter 11, 1523 (1999). 
(3) Y. Regaieg, et al., Materials Letters 80, 195–198 (2012). 
(4) Shuai Zhang, et al., Ceramics International 46, 584–591 (2020). 
(5) Rajasree Das, et al., Ceramics International 47, 393–399 (2021). 

![](https://s3.eu-west-1.amazonaws.com/underline.prod/uploads/markdown_image/1/image/18465c1b9646c15f75f1609bfa70552a.png)

Effect of microwave instant heating on magnetic, electric, thermoelectric and microwave absorption properties of La0.7Na0.3MnO3

Anomalous Nernst effect (ANE) has drawn special attention during the last few years because of its possibility in thermal energy harvesting and fundamental physics involved [1]. Reports on ANE in perovskite oxides are relatively few compared to ferromagnetic metallic alloys. The ANE was previously reported in Sr substituted LaCoO3 [2]. Because of the smaller size of Ca2+ cation compared to Sr2+, magnetic interactions are expected to be modified. Hence, we studied the ANE in La0.5Ca0.5CoO3 for the first time, which shows ferromagnetic ordering at 147 K (Fig. 1(a)). The non-saturating nature of the field dependence of magnetization and its smaller value shown in the inset of Fig. 1(a) indicates the existence of competitive FM-AFM interactions that largely depends on the spin states of the Co3+ and Co4+ ions[2-4]. Such a system can be very interesting to study ANE as the aforementioned competitive effect may dramatically affect the spin-dependent deflection of thermally driven charge carriers. The presence of the ANE in La0.5Ca0.5CoO3 is confirmed from the field dependences of the Nernst thermopower (Sxy) as shown in Fig. 1(b), which shows hysteresis like the magnetization. In this preliminary work, we have carried out ANE measurements only at four selected temperatures. Sxy nearly saturates above 20 kOe at 40 K but not at 100 K, where it has a maximum value at the highest field. The Sxy shows behavior similar to superparamagnetic at 160 K and linear behavior at 200 K with much-reduced values. Magnetic, electrical transport, thermoelectric measurements, and ANE at multiple temperatures will be carried out to realize the mutual effects of magnetism, charge, and heat currents to establish a better relationship between them. This work was supported by the Ministry of Education, Singapore (Grant no. R144-000-422-114 and R144-000-442-114).

![](https://assets.underline.io/uploads/markdown_image/1/image/70f4701c2741c601a6cc175160e1bb04.jpg)

Fig. 1: (a) Temperature dependence of magnetization (M) in La0.5Ca0.5CoO3 . Inset: Field dependence of (b) M at 5 K. and (b) Nernst thermopower (Sxy) measured at T = 40, 100, 160 and 200 K.

Anomalous Nernst effect in perovskite La0.5Ca0.5CoO3

Spin-dependent thermoelectric research has drawn overwhelming attention during the last few years because of its potentiality in energy harvesting and communication applications. Waste heat from locomotives and industries can be converted into electrical and electronic signals to power their own electronics. The Anomalous Nernst effect (ANE) one of the thermomagnetic phenomena proposed to be useful for heat to electrical energy conversion even from a curved surface unlike a conventional thermoelectric module based on semiconductors. Here, we have systematically studied the ANE in polycrystalline metallic perovskite Pr0.5Sr0.5CoO3 as a function of temperature and external magnetic fields. The ANE shows a rapid increase at the onset of ferromagnetic transition (TC ~ 229 K) and after showing a broad maximum at lower temperatures, and it decreases linearly below 100 K. Magnetic field dependence of the ANE, quantified by the transverse Seebeck coefficient (Sxy), exhibits hysteresis below TC as like the magnetization. The maximum saturated value of Sxy due to ANE (~ 0.46 μVK¬-1) found near 175 K (below TC) is ~ 400 times higher than the manganite analog Pr0.5Sr0.5MnO3, and larger than other polycrystalline perovskite oxides reported to date. Our analysis suggests that ANE in this sample is most likely due to asymmetric skew scattering of charge carriers. This work may open a new pathway for the perovskite magnetic oxides for energy-saving applications.

Anomalous Nernst Effect in Bulk Pr0.5Sr0.5CoO3

La1-xSrxCoO3 (LSCO) changes from a paramagnetic semiconductor for x= 0 to a ferromagnetic metal for x≥ 0.2. .Magnetoelastic property of these oxides has been overlooked so far despite it showed giant anisotropic magnetostriction (1000-3000 ppm at 14.2 T) for x = 0.3 and 0.5 [1]. Its origin was suggested to the field-induced spin-state transition [low (S= 0) to intermediate (S= 3/2) spin] of Co3+ ions, and the creation of spin-orbit coupling. Subias et al.[2] report the atomic-scale origin of the magnetostriction in La0.5Sr0.5CoO3 by measuring local changes in Co-O bond length by analyzing the differential X-ray absorption data. Magnetic interactions among Co3+/Co4+ ions and their spin states are sensitive to the crystal field effect and average ionic radius of the rare earth and alkaline earth cations. We successfully synthesized the polycrystalline La0.5Ba0.5CoO3 by microwave irradiation with short-time irradiation of 20 minutes at 1200oC, and measured its magnetization (M) and Joule magnetostriction λpar whose field dependence at 10 K are shown in Fig.1(a). M shows hysteresis at low fields and increases without saturation up to H = 50 kOe. The M value at 50 kOe is much smaller than La0.5Sr0.5CoO3 for which M = 2 μB/f.u.which suggests the lack of long-range ferromagnetic order in this sample. λpar smoothly increases with H without showing a saturation. The value of λpar at 50 kOe is 265 ppm, which is smaller than in LSCO but yet a significant value among most transition metal perovskite oxides. λpar for 50 kOe has the maximum value at 10 K and decreases smoothly as the ferromagnetic -paramagnetic transition is approached (TC = 177 K) and becomes negligible above TC. (see Fig. 1(b)). Work is in progress to correlate the magnetostriction, spin state of Co ions, electronic phase separation, and negative thermal expansion proposed in this compound[3,4] R.M. thanks the Ministry of Education, Singapore (Grant no. R144-000-422-114 and R144-000-442-114).

![](https://assets.underline.io/uploads/markdown_image/1/image/85e902d17082690389e6c12fb4a193f8.jpg)

Fig 1: (a) Field dependence of magnetization (M) on left y-axis and parallel magnetostriction (λpar) on right y-axis of La0.5Ba0.5CoO3 at 10 K. (b) Temperature dependence of the maximum value of λpar at H = 50 kOe on left-yaxis and M for H = 1 kOe on right y-axis.

Magnetostriction in microwave synthesized La0.5Ba0.5CoO3

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Presentations

Effect of microwave instant heating on magnetic, electric, thermoelectric and microwave absorption properties of La0.7Na0.3MnO3

Anomalous Nernst effect in perovskite La0.5Ca0.5CoO3

Anomalous Nernst Effect in Bulk Pr0.5Sr0.5CoO3

Magnetostriction in microwave synthesized La0.5Ba0.5CoO3

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