The discovery of materials with improved functionality can be accelerated by rational material design.1 Heusler compounds with tunable magnetic sublattices allow to implement this concept to achieve novel magnetic properties. 2 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-1 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.Exchange bias corresponds to a shift of the hysteresis loop of a ferromagnet along the magnetic field axis due to interfacial exchange coupling with an adjacent antiferromagnet. fully compensated magnet with a compensation point for a particular Mn/Pt ratio. This design scheme is schematically depicted in Fig. 1. From first-principles calculations, it follows that the critical composition with the zero magnetization is achieved in the solid solution Mn 3−x Pt x Ga at a Pt content of about x 0 = 0.59, which is in good agreement with the experimental findings. On optimizing the Mn/Pt ratio in Mn 3−x Pt x Ga, we always find a small lack of compensation in the material, due to the formation of FM clusters by anti-site disorder. This leads to an exceptionally large bulk EB and a large coercivity. In contrast to an artificial antiferromagnet, which is a thin film structure composed of two ferromagnetic layers separated by a coupling layer 9 , here we combine two isostructural ferrimagnetic compounds Mn 3 Ga and Mn 2 PtGa to obtain an intrinsically anisotropic compensated magnetic state on an atomic scale in a bulk material.In order to characterize the magnetic properties of Mn 3−x Pt x Ga we have measured the temperature dependence of the low field magnetization, M(T ). We find a systematic increase in the 4 ferrimagnetic Néel temperature (T N ) with increasing Mn content as shown in Fig. 2. The irreversibility between the ZFC and FC curves reflects the appearance of coercivity. We suggest that FM clusters embedded in the compensated host are the source of this irreversibility. NMR measurements confirm that these clusters originate from random swaps between Pt in the Mn-Pt planes and Mn in the Mn-Ga planes ( Supplementary Fig. 2). The irreversibility between ZFC and FC M(T ) curves increases with increasing magnetic field demonstrating that cooling in higher fields helps the FM clusters to grow in siz...

Noncollinear magnets provide essential ingredients for the next generation memory technology. It is a new prospect for the Heusler materials, already well known due to the diverse range of other fundamental characteristics. Here, we present a combined experimental and theoretical study of novel noncollinear tetragonal Mn(2)RhSn Heusler material exhibiting unusually strong canting of its magnetic sublattices. It undergoes a spin-reorientation transition, induced by a temperature change and suppressed by an external magnetic field. Because of the presence of Dzyaloshinskii-Moriya exchange and magnetic anisotropy, Mn(2)RhSn is suggested to be a promising candidate for realizing the Skyrmion state in the Heusler family.

Mn2‐based Heusler compounds have attracted a great deal of interest as half‐metallic ferri‐ and ferromagnets and as materials for spintronic applications. In this paper, we report the synthesis, crystal structure, and disorder type of the new Heusler compounds Mn2RuGe, Mn2RhGa, and the redetermination of the crystal structure of Mn2RuSn. They crystallize cubic with L21b structure type in Fm$\bar{3}$m, which is an inverse Heusler structure with a transition metal disorder of the type (Mn0.5,Y0.5)2MnZ (Y = Ru or Rh and Z = Ge, Ga or Sn). It is shown that an inverse Heusler structure can generally gain stability through the configurational part of the entropy of mixing at elevated temperatures without loosing too much enthalpy in the configurational part of the enthalpy of mixing owing to a special bond arrangement in the inverse type structure. The enthalpy of formation of transition‐metal‐based Heusler compounds and Al, Ga, and Ge as the main group metals obtained from DFT calculations and experimental data are used to confirm Burch's rule, which predicts the stability of transition‐metal‐based inverse Heusler compounds. Alloying tendencies as manifested in binary phase diagrams and the enthalpies obtained from the Miedema model are correlated with the stability of Heusler compounds. Burch's rule is in excellent agreement with the current available experimental data. The DFT data and general alloying tendencies show that deviations are expected from this rule. Miedema's model allows the estimation of the enthalpy of formation for the transition‐ and main group metal‐based Heusler compounds, except for those having period 6 elements and Pd.

Noncollinear hexagonal antiferromagnets with almost zero net magnetization were recently shown to demonstrate giant anomalous Hall effect. Here, we present the structural and magnetic properties of noncollinear antiferromagnetic Mn 3 Sn thin films heteroepitaxially grown on Y:ZrO 2 (111) substrates with a Ru underlayer. The Mn 3 Sn films were crystallized in the hexagonal D0 19 structure with c-axis preferred (0001) crystal orientation. The Mn 3 Sn films are discontinuous, forming large islands of approximately 400 nm in width, but are chemical homogeneous and characterized by near perfect heteroepitaxy. Furthermore, the thin films show weak ferromagnetism with an in-plane uncompensated magnetization of M = 34 kA/m and coercivity of μ 0 H c = 4.0 mT at room temperature. Additionally, the exchange bias effect was studied in Mn 3 Sn/Py bilayers. Exchange bias fields up to μ 0 H EB = 12.6 mT can be achieved at 5 K. These results show Mn 3 Sn films to be an attractive material for applications in antiferromagnetic spintronics.

Spintronics is a large field of research that involves the generation, manipulation and detection of spin currents in magnetic heterostructures and the use of these currents to excite and to set the state of magnetic nano-elements. [1,2] The field of spintronics has focused on ferromagnetic thin film structures in which charge currents can be spin-polarized via interfacial and volume spin dependent scattering. However, ferromagnets produce magnetostatic dipole fields, which increase in size as devices are scaled to smaller dimensions. These must be minimized or eleminated to enable operation of spintronic field sensing and magnetic memories. [2] One way to do this is to take advantage of the phenomenon of long-range oscillatory interlayer coupling [3] to create synthetic antiferromagnetic heterostructures [1] or the use of ferrimagnetic materials such as rare-earthtransition metal alloys at their compensation point. [4] The latter ferrimagnetic materials are of special inerest because they can completely eliminate dipole fields volumetrically, even on the atomic scale. However, materials are needed that can operate over a wide temperature window and not solely at or in the vicinity of a compensation temperature. Here we show that Heusler compounds can be designed for this purpose.Heusler compounds, YZ X 2 (where X , Y are transition metals and Z is a main-group 2 element), are well known for their potential applications in spintronics, especially in spin-torque based devices. [5] These materials crystallize in both cubic and tetragonal crystal structures with multiple magnetic sub-lattices, and hence are good candidates for engineering a wide range of complex magnetic structures. In particular all the known tetragonal Heuslers are ferrimagnetic with at least two magnetic sub-lattices whose magnetizations are aligned anti-parallel to one another, or, as has been shown recently, can be non-collinear to one another. The Mn based tetragonal Heuslers are of particular interest because their magnetic ordering temperatures can be well above room temperature, but the magnetizations of their two sub-lattices are typically distinct, leading to a net uncompensated magnetization. One of the most interesting of these materials is Mn3Ga which has a Curie temperature of ~750 K. [6] By tuning the magnetization of the two sublattices in Mn3Ga by changes in composition, we propose that a fully compensated ferrimagnetic (CFI) Heusler is possible. To help identify the needed compositional variations we have carried out density functional calculations of the electronic structures of Mn3-xYxGa   1 0   x (at zero temperature) for the elements = Y Ni, Cu, Rh, Pd, Ag, Ir, Pt, Au, which are non-magnetic or nearly non-magnetic when substituted into Mn3Ga. We show that in all these cases it is theoretically possible to obtain a CFI , which we have experimentally validated for the case of Y=Pt.The present calculation is based on the experimental lattice parameters of the bulk Mn 3 Ga lattice. [6] We find that a compensated mag...

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 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 11.5 nJ cm -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) / 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.

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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 ≤ x ≤ 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 K u ≥ 1.4 MJ/m 3 , 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 K u of 1.47 MJ/m 3 and energy product (BH) max of 37 kJ/m 3 , 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.