In this paper, the magnetic and electrocatalytic properties of hydrothermally grown transition metal doped (10% of Co, Ni, Fe, and Mn) 2H-MoS2 nanocrystals (NCs) with a particle size 25-30 nm are reported. The pristine 2H-MoS2 NCs showed a mixture of canted anti-ferromagnetic and ferromagnetic behavior. While Co, Ni, and Fe doped MoS2 NCs revealed room temperature ferromagnetism, Mn doped MoS2 NCs showed room temperature paramagnetism, predominantly. The ground state of all the materials is found to be cantedantiferromagnetic phase. To study electrocatalytic performance for hydrogen evolution reaction, polarization curves were measured for undoped and the doped MoS2 NCs. At the overpotential of η = −300 mV, the current densities, listed from greatest to least, are FeMoS2, CoMoS2, MoS2, NiMoS2, and MnMoS2, and the order of catalytic activity found from Tafel slopes is CoMoS2 > MoS2 > NiMoS2 > FeMoS2 > MnMoS2. The increasing number of catalytically active sites in Co doped MoS2 NCs might be responsible for their superior electrocatalytic activity. The present results show that the magnetic order-disorder behavior and catalytic activity can be modulated by choosing the suitable dopants in NCs of 2D materials.

The magnetism of the double perovskite compounds La2−xSrxFeCoO6 (x = 0, 1, 2) are contrasted using magnetization, neutron diffraction and electron paramagnetic resonance with the support from density functional theory calculations. La2FeCoO6 is identified as a long-range ordered antiferromagnet displaying a nearroom temperature transition at TN = 270 K, accompanied by a low temperature structural phase transition at TS = 200 K. The structural phase transformation at TS occurs from R3c at 300 K to P nma at 200 K. The density functional theory calculations support an insulating non-compensated AFM structure. The long-range ordered magnetism of La2FeCoO6 transforms to short-range glassy magnetism as La is replaced with Sr in the other two compounds. The magnetism of La2FeCoO6 is differentiated from the non-equilibrium glassy features of Sr2FeCoO6 and SrLaFeCoO6 using the cooling-and-heating-in-unequal-fields (CHUF) magnetization protocols. This contransting magnetism in the La2−xSrxFeCoO6 series is evidenced in electron paramegnetic resonance studies. The electronic density-of-states estimated using the density functional theory calculations contrast the insulating feature of La2FeCoO6 from the metallic nature of Sr2FeCoO6. From the present suite of experimental and computational results on La2−xSrxFeCoO6, it emerges that the electronic degrees of freedom, along with antisite disorder, play an important role in controlling the magnetism observed in double perovskites.

The critical phenomena and magnetic entropy of the quasi-2D ferrimagnetic crystal, Mn3Si2Te6 (MST), is analyzed along the easy axis (H || ab) as a function of proton irradiance. The critical exponents β and γ do not fall into any particular universality class upon proton irradiation. However, for pristine and irradiated samples, the critical exponents lie closer to mean field-like interactions; therefore, long-range interactions are presumed to be sustained in MST. The effective spatial dimensionality reveals that MST remains at d=3 under proton irradiation, whereas spin dimensionality transitions from an initial n=1 to n=2 and n=3 for 1 × 1015 and 5 × 1015 H+/cm2, indicating XY and Heisenberg interactions, respectively. The spin correlation function reveals an increase in magnetic correlations at 5 × 1015 H+/cm2. Maximum change in magnetic entropy at 3 T is the largest for 5 × 1015 H+/cm2 at 2.45 J/kg K, in comparison to 1.60 J/kg K for pristine MST. These results intriguingly align with previous findings on MST where magnetization increased by ∼50% at 5 × 1015 H+/cm2, in comparison to its pristine counterpart [Martinez et al., Appl. Phys. Lett. 116, 172404 (2020)]. Magnetic entropy derived from heat capacity analysis shows no large deviations across the proton irradiated samples suggesting that the antiferromagnetic (AFM) coupling between the Mn sites is stable even after proton irradiation. This implies that magnetization is enhanced through a strengthening of the super-exchange interaction between Mn atoms mediated through Te rather than a weakening of the AFM component.

Developing functional, cleavable two-dimensional materials for use in next generation devices has recently become a topic of considerable interest due to their unique properties. Of particular interest, transition metal halides CrI3 and CrCl3 have shown to be good contenders for tunable and cleavable magnetic materials due to their unique magnetic properties in the monolayer. Here, electron spin resonance spectroscopy is used to pinpoint the atomic origins and underlying mechanisms of magnetic interactions as a function of temperature (5-500 K) and microwave frequency (9.43, 120 GHz) on CrI3 and CrCl3 bulk single crystals. ESR signals from CrI3 due to Cr3+ were observed to decay at 460 K, while ESR signals from CrCl3 remain up to 500 K. In the case of CrCl3, the temperature dependences of signal behavior, line width and g-value show characteristic signatures of ferromagnetic fluctuations at around 40 K, near to the antiferromagnetic phase transition at 17 K.

The bulk van der Waals crystal Mn3Si2Te6 (MST) has been irradiated with a proton beam of 2 MeV at a fluence of 1×1018 H+ cm-2. The temperature dependent magnetization measurements show a drastic decrease in the magnetization of 49.2% in the H//c direction observed in ferrimagnetic state. This decrease in magnetization is also reflected in the isothermal magnetization curves. No significant change in the ferrimagnetic transition temperature (75 K) was reflected after irradiation. Electron paramagnetic resonance (EPR) spectroscopy shows no magnetically active defects present after irradiation. Here, experimental findings gathered from MST bulk crystals via magnetic measurements, magnetocaloric effect, and heat capacity are discussed.