Exceptional tunability in the electronic and magnetic properties makes Heusler compounds very promising from both the fundamental and applied perspectives. Half-metallic ferromagnetism, half-metallic fully-compensated ferrimagnetism, spin-gapless semiconducting behavior, and fully-compensated ferrimagnetic spin-gapless semiconducting behavior have been predicted or demonstrated experimentally in Heusler compounds which makes them suitable for applications in a number of novel spintronic devices1,2,3,4,5. Half-metallic Co-based Heusler alloys are among the most attractive systems due to their high Curie temperatures, high spin polarization and the structural similarity to binary semiconductors6,7,8. Spin-gapless semiconductors can be regarded as a combination of gapless semiconductors and half-metallic ferromagnets where the conducting electrons or holes are not only 100% spin polarized but also easily excited. The realization of spin-gapless semiconducting behavior in Heusler alloys is expected to fulfill the needs for semiconductor spintronics. In this work, we have introduced the substitution of low valence transition metal atoms Y = Ti, V, Cr, Mn, and Fe to Co atoms in the parent Co2FeGa system, and examined the properties of quaternary Heusler compounds Co2-xYxFeGa (x = 0.50), both experimentally and theoretically to get a global overview of the electronic, magnetic, electron transport and mechanical properties. All single-phase alloys exhibit Heusler like L21 ordering, as corroborated by X-ray diffraction. The low-temperature saturation magnetic moments agree fairly well with the values expected from a Slater-Pauling rule for half metals (Fig.1). Electrical transport measurements are performed to explain the electronic structure of the alloys. The temperature dependence of electrical resistivity for Mn substituted alloy shows semiconducting nature in the complete temperature regime (5-400)K (Fig.2). Ab initio calculations are also performed to understand the experimental findings.

![](https://assets.underline.io/uploads/markdown_image/1/image/14f7b59db99b038cf74a4718f8f85273.jpg)

The variation of saturation magnetic moment with valence electron counts per formula units with element Y.

![](https://assets.underline.io/uploads/markdown_image/1/image/4d76d8c1a433798c5183033756315811.jpg)

Temperature dependence of electrical resistivity in Co1.50Mn0.50FeGa at zero magnetic field showing semiconducting behavior.

Possible half-metallic and spin-gapless semiconducting behavior in quaternary Heusler compounds Co2-xYxFeGa (Y = Ti, V, Cr, Mn, Fe, and Co, x = 0.50)

The realization of physical systems whose electronic and magnetic properties can be easily manipulated by playing with valence electrons are very promising from both the fundamental and applied perspectives. Half-metallic ferromagnets are ideal candidates for spintronic applications because of their high spin polarization of charge carriers at the Fermi level [1,2]. High Curie temperature is one of the important precondition of the half-metallic ferromagnets from the application point of view. Co2- based intermetallic Heusler alloys (L21 structure, space group Fm-3m, # 225) are among the most attractive half-metallic systems due to their high Curie temperatures, high spin polarization and the structural similarity to binary semiconductors [1,2]. The Co2FeSi (CFS) system is one such candidate of interest for spintronic applications due to its high Curie temperature crystallizing in the L21 structure but Fermi level falls on the edge of the minority conduction band (in both generalized gradient approximation (GGA) and GGA+U approach) making the system shy from being robust half metallic. High Tc = 1100K and large magnetic moment of 6.00 μB/f.u. is reported in Ref [3]. If one of the Co atom in CFS is replaced by low valence transition metal atom Y = Sc, Ti, V, Cr, Mn, and Fe, alloys with rich and useful properties can be tailored. The quaternary Heusler alloy CoFeMnSi [4] is observed theoretically and experimentally to be spin gapless semiconductor, CoFeCrSi [5] is reported to be half-metallic with some structural disorder, CoFeVSi and CoFeTiSi are reported theoretically to be nearly half-metallic and half-metallic respectively, but both are observed experimentally to show multi-phase behavior in bulk form. The Fermi level lies on the edge of the minority valence band in all Y substituted quaternary Heusler alloys, leading to an unstable half-metallicity. So, as we go from CFS to CoFeYSi, Fermi level is shifted from lower edge of conduction band to upper edge of valence band in minority spin channel which is in accordance to Ref. [2,6]. They have suggested that an expansion of the lattice should shift the Fermi level deeper in energy and the contraction should shift it higher in energy. Therefore, one can expect robust half metallicity with Fermi level exactly at the middle of the band gap for some intermediate Y concentrations in CFS due to the expansion of the lattice when Y with larger atomic radius substitutes for Co. The substitution of Y to Co may be also seen as d-electron deficiency. In this work, we have introduced the substitution of all low valence transition metal atoms Y = Sc, Ti, V, Cr, Mn, and Fe to Co atoms in the parent CFS system, and examined the structural, electronic, magnetic, and mechanical properties of quaternary Heusler compounds Co2-xYxFeSi (0≤x≤1) to get a global overview of the electronic, magnetic and mechanical properties, promising candidates for spintronics applications. All single phase alloys exhibit face centered cubic crystal structure with a strong tendency towards L21 ordering, as corroborated by X-ray diffraction. The low-temperature saturation magnetic moments agree fairly well with our theoretical results and also obey the Slater-Pauling rule, a prerequisite for half metallicity. Fig.1 shows the linear decrease of the spontaneous magnetizations measured at 2K with the valence electron counts per formula units with element Y = Ti, V, Cr, Mn, Fe, and Co in Co2-xYxFeSi (x = 0.50). All alloys are soft ferromagnets with high Curie temperatures, ranging from 700K to 1100K, allowing for applications at room temperature and above. The Curie temperatures are observed to vary almost linearly with the saturation magnetic moment which is also expected in half-metallic systems. First-principles calculations also predicted finite band gap in the minority spin channel for most of the alloys in Co2-xYxFeSi series. Fig. 2 shows the calculated density of states (DOS) plots using GGA approach for majority and minority spin channels of Co2-xMnxFeSi (0≤x≤1) alloys, where the Fermi level is represented by the zero energy. It can be seen clearly that the system exhibits half-metallic behavior after Mn substitution. In the case of parent compound CFS, there is significant amount of DOS at the Fermi level on both the spin channels. After Mn substitution, the Fermi level is observed to shift deeper in energy-levels and falls at the middle of the energy gap on spin down channel for x = 0.50. Further increase of Mn content shifts the Fermi level towards the lower edge of energy gap due to lattice expansion. But, still Fermi level lies within energy gap making the system Half-metallic. In addition, conduction band and valence band in majority spin channel touch each other at Fermi level in x = 1, making the system spin gapless semiconductor. The energy gap is observed to increase with the increase of Mn content. Although, the calculated minority spin gap is the highest for x = 1, the half-metallic gap is greater for x = 0.50. Relatively high mechanical hardness values among the reported Heusler alloys are also observed, approaching 16 GPa for the most Ti-rich material [6-8].

**References:**

1. C. Felser, G. H. Fecher, and B. Balke, Angewandte Chemie International Edition, 46, 668 (2007). 2. I. Galanakis, P. Dederichs and N. Papanikolao, Physical Review B, 66, 174429 (2002). 3. E. Fischer, J. Karel and S. Fabbrici, Physical Review B, 94, 024418 (2016). 4. L. Bainsla, A.I. Mallick and M.M. Raja, Physical Review B, 91, 104408 (2015). 5. Y. Jin, P. Khareland P. Lukashev, Journal of Applied Physics, 120, 053903 (2016). 6. R. Mahat, S. KC and U. Karki, Physical Review B, Submitted (2021). 7. R. Mahat, S. KC and D. Wines, Journal of Alloys and Compounds, 830, 154403 (2020). 8. R. Mahat, S. KC and D. Wines, Journal of Magnetism and Magnetic Materials, 521, 167398 (2021).

**Images:**

![](https://assets.underline.io/uploads/markdown_image/1/image/7c947ceb5f0d173267903a665062a366.jpg)
Fig.1. The saturation magnetic moment versus valence electron counts per formula units with element Y = Ti, V, Cr, Mn, Fe, and Co in Co2-xYxFeSi (x = 0.50), both experimental and expected from Slater Pauling rule for half metals. The black data points represent reported literature values [3].

![](https://assets.underline.io/uploads/markdown_image/1/image/42867fe7839357c6b915951bb21bee55.jpg)
Fig.2. Spin polarized total DOS for Co2-xYxFeSi (Y = Mn, 0≤x≤1). Number of states is scaled with respect to one formula unit.

 Effect of mixing the low-valent transition metal atoms Y = Sc, Ti, V, Cr, Mn and Fe on the properties of quaternary Heusler compounds Co2-xYxFeSi (0≤x≤1)

Co2- based intermetallic Heusler alloys are among the most attractive half-metallic systems due to their high Curie temperatures, high spin polarization and the structural similarity to binary semiconductors [1,2]. The Co2FeGe system is one such candidate of interest for spintronic applications, but experimentally it does not form a single phase in bulk form [3,4,5]. In this work, we have introduced Cr doping to stabilize the Co2FeGe system, and examined the structural, magnetic, transport, and mechanical properties of quaternary Heusler alloys Co2-xCrxFeGe with 0 ≤ x ≤ 1, both experimentally and theoretically. Single phase microstructures are observed for Cr compositions from x = 0.25 to x = 1. The samples with Cr concentrations below x = 0.25 are multi-phase. XRD patterns at room temperature show the presence of ordered Y structure (space group F-43m, # 216) for all single-phase samples. The low-temperature saturation magnetic moments agree fairly well with our theoretical results and also obey the Slater-Pauling rule, a noted prerequisite for half metallicity. The Density functional theory calculations performed using VASP code with projector augmented wave method (PAW) and the Perdew-Burke-Enzerhof (PBE) functional predict half-metallic character in the alloys after Cr substitution. All alloys are observed to have high Curie temperatures, and show a linear dependence with the saturation magnetic moment which is expected in half metallic Co-based Heusler alloys [6]. Transport measurements were performed to explain the electronic structure of the alloys. High mechanical hardness values are also observed which makes these materials suitable for industrial applications requiring repetitive thermal cycling and resist cracking from vibrations.References: 1. I. Galanakis, P. Dederichs, and N. Papanikolaou, Physical Review B 66, 174429 (2002). 2. C. Felser, G. H. Fecher, and B. Balke, Angewandte Chemie International Edition 46, 668(2007). 3. K. R. Kumar, K. K. Bharathi, J. A. Chelvane, IEEE Transactionson Magnetics 45, 3997 (2009). 4. S. KC, R. Mahat, P. LeClair, Phys. Rev. Materials 3 (2019) 114406. 5. R. Mahat, S. KC, D. Wines, P. LeClair, Bulletin of the American Physical Society (2020). 6. G. H. Fecher, H. C. Kandpal, S. Wurmehl, C. Felser, Journal of applied Physics 99, 08J106 (2006).

Possible Half-Metallic Behavior of Co2-xCrxFeGe Heusler Alloys: Theory and Experiment

**Session chair:** Atsufumi Hirohata, University of York



BOA - Magnetoelectronic Materials and Phenomena: Heuslers and Related Materials

technical paper

The 15th Joint MMM-INTERMAG Conference (2022 Joint) is sponsored jointly by AIP Publishing and the IEEE Magnetics Society. Members of the international scientific and engineering communities interested in recent developments in fundamental and applied magnetism are invited to attend and contribute to the technical sessions. The technical program will include invited and contributed papers in oral and poster sessions, invited symposia, a plenary session, and an evening session, with about 1500 presentations overall. This Conference provides an outstanding opportunity for worldwide participants to meet their colleagues and collaborators and discuss developments in all areas of magnetism research.

The 2022 Joint Conference will offer both in-person and prerecorded on-demand content.

For tickets to the event, please register at the following link: https://magnetism.org/register

Please register for the Joint MMM-Intermag conference to join the event.

2022 Joint MMM-INTERMAG

This Conference provides an outstanding opportunity for worldwide participants to meet their colleagues and collaborators and discuss developments in all areas of magnetism research.

*Session Chair: Stella Skiadopoulou, The University of Dublin Trinity College*

These on-demand presentations are available to view at your leisure.

DP: Multiferroics and Magnetoelectrics: Phenomena, Materials and Transport

poster

INTERMAG 2021 Welcome Video



	
<figure class="video_container">
 <iframe src="https://screencast-o-matic.com/player/crflqFVnUpZ?v=6&ff=1&title=0&controls=1" width=640 height=360 frameborder="0" allowfullscreen="true"> </iframe>
</figure>

Want to buy a ticket? 

Register for INTERMAG 2021 here

[![](https://assets.underline.io/uploads/markdown_image/1/image/17ce76e7960db633258024eef8d6da7f.png)](https://intermag.org/register)

Got your ticket, but still can’t access the event?

Contact us and our team will look into it.

INTERMAG 2021

E1: Half-Metallic Materials

The 65th Annual Conference on Magnetism and Magnetic Materials (MMM 2020) was held in a virtual form. The COVID-19 pandemic, with its associated uncertainty about international travel and the ability to gather in large groups, meant that the Steering Committee decided to cancel the face-to-face meeting that had been planned in Palm Beach, Florida November 2-6, 2020.

We were reluctant to give up the benefits of meeting face-to-face, and know that shifting to a virtual conference is a significant change for this community. Nevertheless, we are first and foremost concerned about the health and safety of all our Conference participants and their loved ones on returning home after travelling.

The MMM 2020 Steering Committee was working exceptionally hard, along with our sponsors, the IEEE Magnetics Society and AIP Publishing, to make this event serve the needs of our participants, who live in time zones all around the globe, in the best possible way. 

You need a ticket to explore this event.

If you have already registered for MMM 2020, and you have already created an account, then you
just need to login (above).

If you have already registered for MMM 2020, but you have not yet created an account, then you
need to click on &quot;create an account&quot; (above) and then login.

Forgot your password? Go to
https://www.underline.io/log-in

If you have not yet registered for MMM 2020 but would like to do so, go to
https://magnetism.org/register

Still need help? Contact our team!


Rabin Mahat

3

3

SHORT BIO

Presentations

Possible half-metallic and spin-gapless semiconducting behavior in quaternary Heusler compounds Co2-xYxFeGa (Y = Ti, V, Cr, Mn, Fe, and Co, x = 0.50)

Effect of mixing the low-valent transition metal atoms Y = Sc, Ti, V, Cr, Mn and Fe on the properties of quaternary Heusler compounds Co2-xYxFeSi (0≤x≤1)

Possible Half-Metallic Behavior of Co2-xCrxFeGe Heusler Alloys: Theory and Experiment

Stay up to date with the latest Underline news!

PRESENTATIONS

CONFERENCES

COMPANY

RESOURCES