LaMn3+O3 is an AFM insulator with TN = 140 K but transforms into a FM insulator with Co2+ or Ni2+ substituted at the Mn-site in La2CoMnO6 and La2NiMnO6 (1), accompanied by a change of Mn valence from 3+ to 4+. However, LaMn0.96Mo0.04O3 is a metallic ferromagnet at low temperatures (2). The FM Curie temperature TC decreased only by 7 K upon 6% Mo6+: d0 substitution in La0.67Sr0.33Mn1-xMoxO3 (3). It was stated that Mo6+ doping induced Mn2+ (d5) which interacted with Mn3+(d4) through Zener’s double exchange giving rise to FM and metallic behavior. But, studies on Mo-doped manganites are yet rare. Here, we report the physical characterization of LaMn0.94Mo0.06O3 prepared by solid-state route. Fig.1(a) shows the temperature dependence of magnetization (M) and inverse susceptibility (Χ-1) measured under H = 1kOe. Fig. 1(b) shows the dc resistivity (ρ) and thermopower (S). Tc obtained from the inflection point of dM/dT is 237 K whereas the Χ-1 deviates from the Curie-Weiss behavior below 260 K. This is possibly due to Griffiths phase, i.e. nano-sizes FM clusters preformed above TC in the PM matrix. The ρ shows an IM transition with a peak at 235 K. However, S shows a peak around 258 K, which is about 20 K above the TC, suggesting that S is sensitive to nucleation of FM nano domains or short-range FM correlation. Fig. 1(c) shows ESR signal as a derivative microwave absorption as a function of dc magnetic field at selected temperatures near FM transition. The spectrum at 300 K is typical of ESR. While the spectrum at 300 K can be fitted to a single Lorentzian curve, the spectrum at 250 K reveals another low-intensity peak at a lower field (~1900 Oe) in addition to the ESR signal around 3200 Oe. The intensity of the ESR-signal decreases dramatically at 245 K but the intensity of the low-field peak increases. At 230 K, we do not see the ESR signal. These results indicate that the low field peak is due to FMR, but this feature start appearing above TC confirms that FM metallic nano domains are preformed above TC in the PM state and increase in size with lowering temperature and percolate leading to long-range FM and metallicity. 

**References:** (1) G. Blasse, Ferromagnetic interactions in non-metallic perovskites, J. Phys. Chem. 26, 1969 (1965);S. Vasala and M. Karppinen, A2B’B’’O6 perovskites: A review, Prog. Soild State Chem. 42, 1 (2015). 

(2) W. J. Lu et al., Induced ferromagnetism in Mo-substituted LaMnO3, Phys. Rev. B, 73, 174425 (2006). 

(3) L. Chen et al., Critical behavior of Mo-doping La0.67Sr0.33M1-xMoxO3 perovskite, Physica B, 404,1879 (2009). 

R. M. thanks the Ministry of Education, Singapore for supporting this work (Grant no. R144-000-442-114)


(a) T-dependence of M and X-1; (b) T-dependence of ρ and S; 1(c) ESR at selected T

Magnetism and Electron Spin Resonance (ESR) in Mo doped LaMnO3

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

Recently, ferromagnetic resonance (FMR) in insulating YIG film was shown to be driven by microwave current in the Pt film deposited on the top of YIG film and detected as a dc voltage in the Pt layer due to spin Hall effect and/or spin rectification[1,2]. Here, we demonstrate an alternative method to study FMR in ceramic YIG. A polycrystalline pellet was made from YIG nanopowder by sintering in the air at 900oC for 12 hr. Magnetization at 300K, shown in the main panel of Fig.1(a), affirms the soft ferromagnetic nature of YIG. The upper inset in (a) illustrates the sketch of our experimental setup. Since the resistance of YIG could not be measured by the impedance analyzer, a layer of silver paint was coated on the top surface of the sample and at two ends to allow radio-frequency current to flow. The sample bridges the signal line and the ground plane of the sample stage, which is connected to the impedance analyzer via a rigid coaxial cable. A microwave signal is injected into the Ag paint layer through the signal line. Resistive and reactance of the Ag-paint were measured while sweeping frequency at different values of the dc magnetic field,H. The lower inset shows magnetoresistance MR(b) and magnetoreactance MX(c) for five frequencies (f) as H decreased from 3 kOe to 0 Oe. The MR of the Ag-paint for 3 GHz exhibits a prominent peak at H = Hr around which MX crosses zero. Both the amplitude of the peak in MR and Hr decreases as f decreases. We argue that the peak in MR is caused by FMR. The inset shows the dependence of Hr on f and we are able to fit the data with Kittel’s relation for in-plane FMR. The observed electrical detection of FMR in YIG with colloidal silver particles having weak spin-orbit coupling than Pt deserves an urgent understanding. R. M. thanks the Ministry of Education, Singapore for support (Grant no. R144-000-442-114).

![](https://assets.underline.io/uploads/markdown_image/1/image/ae1fde754d75a41639f3df99d02d023b.jpg)

Fig. 1 (a) M-H isotherm of YIG sample at 300 K(main panel) and the schematic diagram of the experimental setup (upper inset). Field dependence of (b) magnetoresistance MR)and (c) magnetoreactance MX at selected frequencies of current excitation (bottom inset). Inset in (b) shows the frequency dependence of the resonance field (symbols) and Kittel's fit for FMR.

Electrically detected ferromagnetic resonance in polycrystalline YIG covered with a layer of Ag paint

We describe a simple experimental method to detect electron paramagnetic resonance (EPR) in polycrystalline 2,2-diphenyl-1-picrylhydrazyl (DPPH) sample, the standard g-marker for EPR spectroscopy, without using a cavity resonator or a prefabricated waveguide. It is shown that microwave (MW) current injected into a layer of silver paint coated on an insulating DPPH sample can excite the paramagnetic resonance in DPPH. As the applied dc magnetic field H is swept, the high-frequency resistance of the Ag-paint layer, measured at room temperature with a single port impedance analyzer in the MW frequency range f = 1 to 2.5 GHz, exhibits a sharp peak at a critical value of the dc field (H = Hr) while the reactance exhibits a dispersion-like behavior around the same field value for a given f. Hr increases linearly with f. We interpret the observed features in the impedance to EPR in DPPH driven by the Oersted magnetic field arising from the MW current in the Ag-paint layer. We also confirm the occurrence of EPR in DPPH independently using a co-planar waveguide based broadband technique in the frequency range 2 – 4 GHz. This technique has the potential to investigate other EPR active inorganic and organic compounds.

Electrically Detected Paramagnetic Resonance in Ag-paint Coated Polycrystalline DPPH

BOA: Complex Oxides

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Magnetism and Electron Spin Resonance (ESR) in Mo doped LaMnO3

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

Electrically detected ferromagnetic resonance in polycrystalline YIG covered with a layer of Ag paint

Electrically Detected Paramagnetic Resonance in Ag-paint Coated Polycrystalline DPPH

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