Heteroepitaxial growth of tetragonal Mn2.7−x_{2.7-x}Fex_{x}Ga1.3_{1.3} (0 ⩽\leqslant x ⩽\leqslant 1.2) Heusler films with perpendicular magnetic anisotropy

This work reports on the structural and magnetic properties of Mn$_{2.7-x}$Fe$_{x}$Ga$_{1.3}$ Heusler films with different Fe content x (0 $\leqslant$ x $\leqslant$ 1.2). The films were deposited heteroepitaxially on MgO single crystal substrates, by magnetron sputtering. Mn$_{2.7-x}$Fe$_{x}$Ga$_{1.3}$ films with the thickness of 35 nm were crystallized in tetragonal D0$_{22}$ structure with (001) preferred orientation. Tunable magnetic properties were achieved by changing the Fe content x. Mn$_{2.7-x}$Fe$_{x}$Ga$_{1.3}$ thins films exhibit high uniaxial anisotropy Ku $\geqslant$ 1.4 MJ/m3, coercivity from 0.95 to 0.3 T and saturation magnetization from 290 to 570 kA/m. The film with Mn$_{1.6}$Fe$_{1.1}$Ga$_{1.3}$ composition shows high Ku of 1.47 MJ/m3 and energy product ${(BH)_{max}}$ of 37 kJ/m3, at room temperature. These findings demonstrate that Mn$_{2.7-x}$Fe$_{x}$Ga$_{1.3}$ films have promising properties for mid-range permanent magnet and spintronic applications.Comment: 13 pages, 5 figures and 2 table

Design of compensated ferrimagnetic Heusler alloys for giant tunable exchange bias

The discovery of materials with improved functionality can be accelerated by rational material design. Heusler compounds with tunable magnetic sublattices allow to implement this concept to achieve novel magnetic properties. Here, we have designed a family of Heusler alloys with a compensated ferrimagnetic state. In the vicinity of the compensation composition in Mn-Pt-Ga, a giant exchange bias (EB) of more than 3 T and a similarly large coercivity are established. The large exchange anisotropy originates from the exchange interaction between the compensated host and ferrimagnetic clusters that arise from intrinsic anti-site disorder. We demonstrate the applicability of our design concept on a second material, Mn-Fe-Ga, with a magnetic transition above room temperature, exemplifying the universality of the concept and the feasibility of room-temperature applications. Our study points to a new direction for novel magneto-electronic devices. At the same time it suggests a new route for realizing rare-earth free exchange-biased hard magnets, where the second quadrant magnetization can be stabilized by the exchange bias.Comment: Four figure

Epitaxial growth, structural characterization and exchange bias of non-collinear antiferromagnetic Mn3_{3}Ir thin films

Antiferromagnetic materials are of great interest for spintronics. Here we present a comprehensive study of the growth, structural characterization, and resulting magnetic properties of thin films of the non-collinear antiferromagnet Mn$_{3}$Ir. Using epitaxial engineering on MgO (001) and Al$_{2}$O$_{3}$ (0001) single crystal substrates, we control the growth of cubic ${\gamma}$-Mn$_{3}$Ir in both (001) and (111) crystal orientations, and discuss the optimization of growth conditions to achieve high-quality crystal structures with low surface roughness. Exchange bias is studied in bilayers, with exchange bias fields as large as -29 mT (equivalent to a unidirectional anisotropy constant of 11.5 nJ cm$^{-2}$) measured in Mn$_{3}$Ir (111) / permalloy heterostructures at room temperature. In addition, a distinct dependence of blocking temperature on in-plane crystallographic direction in Mn$_{3}$Ir (001) / Py bilayers is observed. These findings are discussed in the context of chiral antiferromagnetic domain structures, and will inform progress towards topological antiferromagnetic spintronic devices.Comment: 15 pages, 10 figure

Co3O4-gamma-Fe2O3 Nanocrystal Heterostructures with Enhanced Coercivity and Blocking Temperature

Nethravathi C, Rajamathi CR, Caron L, et al. Co3O4-gamma-Fe2O3 Nanocrystal Heterostructures with Enhanced Coercivity and Blocking Temperature. JOURNAL OF PHYSICAL CHEMISTRY C. 2020;124(2):1623-1630.Reassembly of alpha-cobalt hydroxide nanosheets in the presence of citrate-capped gamma-Fe2O3 nanoparticles yields a-cobalt hydroxide-gamma-Fe(2)O(3 )hybrid in which the nanoparticles are trapped between the nanosheets. Thermal decomposition of the hybrid yields the Co3O4-gamma-Fe2O3 heterostructure. While the saturation magnetization (M-s) of gamma-Fe2O3 is preserved in the Co3O4-gamma-Fe(2)O(3 )heterostructure, the interface between the oxides in the heterostructure enhances the coercive field (H-C) to a large extent. The coercivity persists even above the Neel temperature of Co3O4 with the blocking temperature increased beyond room temperature. The unique morphology of the heterostructure wherein the Co3O4 and gamma-Fe2O3 particles are fused together to form a larger network leading to strong interparticle interactions, diffusion of Co atoms into the surface of gamma-Fe(2)O(3 )particles, and strain at the interfaces appear to be the reasons behind the improved magnetic behavior

Epitaxial growth, structural characterization, and exchange bias of noncollinear antiferromagnetic Mn3Ir thin films

Antiferromagnetic materials are of great interest for spintronics. Here we present a comprehensive study of the growth, structural characterization, and resulting magnetic properties of thin films of the noncollinear antiferromagnet Mn3Ir. Using epitaxial engineering on MgO (001) and Al2O3 (0001) single-crystal substrates, we control the growth of cubic γ-Mn3Ir in both (001) and (111) crystal orientations, and discuss the optimization of growth conditions to achieve high-quality crystal structures with low surface roughness. Exchange bias is studied in bilayers, with exchange bias fields as large as -29 mT (equivalent to a unidirectional anisotropy constant of 0.115ergcm-2 or 11.5nJcm-2) measured in Mn3Ir (111)/Permalloy heterostructures at room temperature. In addition, a distinct dependence of blocking temperature on in-plane crystallographic direction in Mn3Ir (001)/Permalloy bilayers is observed. These findings are discussed in the context of antiferromagnetic domain structures, and will inform progress towards chiral antiferromagnetic spintronic devices.</p