29 research outputs found
Ballistic spin-transport properties of magnetic tunnel junctions with MnCr-based ferrimagnetic quaternary Heusler alloys
We investigate the suitability of nearly half-metallic ferrimagnetic
quaternary Heusler alloys, CoCrMnZ (Z=Al, Ga, Si, Ge) to assess the feasibility
as electrode materials of MgO-based magnetic tunnel junctions (MTJ). Low
magnetic moments of these alloys originated from the anti-ferromagnetic
coupling between Mn and Cr spins ensure a negligible stray field in spintronics
devices as well as a lower switching current required to flip their spin
direction. We confirmed mechanical stability of these materials from the
evaluated values of elastic constants, and the absence of any imaginary
frequency in their phonon dispersion curves. The influence of swapping
disorders on the electronic structures and their relative stability are also
discussed. A high spin polarization of the conduction electrons are observed in
case of CoCrMnZ/MgO hetrojunctions, independent of terminations at the
interface. Based on our ballistic transport calculations, a large coherent
tunnelling of the majority-spin -like states can be expected
through MgO-barrier. The calculated tunnelling magnetoresistance (TMR) ratios
are in the order of 1000\%. A very high Curie temperatures specifically for
CoCrMnAl and CoCrMnGa, which are comparable to Co, could also yield a
weaker temperature dependece of TMR ratios for CoCrMnAl/MgO/CoCrMnAl (001) and
CoCrMnGa/MgO/CoCrMnGa (001) MTJ.Comment: 24 pages, 13 figure
Electronic and magnetic properties of the topological semimetal SmMgBi
Dirac semimetals show nontrivial physical properties and can host exotic
quantum states like Weyl semimetals and topological insulators under suitable
external conditions. Here, by combining angle-resolved photoemission
spectroscopy measurements (ARPES) and first-principle calculations, we
demonstrate that Zintl-phase compound SmMgBi belongs to the close
proximity to a topological Dirac semimetallic state. ARPES results show a
Dirac-like band crossing at the zone-center near the Fermi level () which is further confirmed by first-principle calculations. Theoretical
studies also reveal that SmMgBi belongs to a topological class
and hosts spin-polarized states around the . Zintl's theory
predicts that the valence state of Sm in this material should be Sm,
however we detect many Sm-4 multiplet states (flat-bands) whose energy
positions suggest the presence of both Sm and Sm. It is also
evident that these flat-bands and other dispersive states are strongly
hybridized when they cross each other. Due to the presence of Sm ions,
the temperature dependence of magnetic susceptibility shows
Curie-Weiss-like contribution in the low temperature region, in addition to the
Van Vleck-like behaviour expected for the Sm ions. The present study
will help in better understanding of the electronic structure, magnetism and
transport properties of related materials.Comment: 10 pages, 7 figure
Anisotropic magnetism and electronic structure of trigonal EuAlGe single crystals
The magnetic and electronic properties of the layered Zintl-phase compound
EuAlGe crystallizing in the trigonal CaAlSi-type structure are
reported. Our neutron-diffraction measurements show that EuAlGe
undergoes A-type antiferromagnetic (AFM) ordering below ~K, with the Eu moments (Eu, ) aligned
ferromagnetically in the plane. The magnetic structure consists of
trigonal AFM domains associated with -plane magnetic anisotropy and a
field-induced reorientation of the Eu spins in the domains is evident at ~K below the critical field kOe. Electrical resistivity and
ARPES measurements show that EuAlGe is metallic both above and below
. In the AFM phase, we directly observe folded bands in ARPES due to
the doubling of the magnetic unit cell along the axis with an enhancement
of quasiparticle weight due to the complex change in the coupling between the
magnetic moments and itinerant electrons on cooling below . The
observed electronic structure is well reproduced by first-principle
calculations, which also predict the presence of nontrivial electronic states
near the Fermi level in the AFM phase with topological numbers 1;(000).Comment: 16 pages, 13 captioned figures, 53 references Updated several
affiliation
Experimental inspection of a computationally-designed NiCrMnSi Heusler alloy with high Curie temperature
Nowadays advanced magnetic tunnel junction applications demand very high tunnel magnetoresistance at room temperature, thus it is quite important to explore high Curie temperature Tc half-metallic Heusler alloys. In this article rst-principles calculation unveiled that NiCrMnSi has Tc of 1200 K comparable to that of the traditional Co2MnSi Heusler alloys, even though it does not contain Co element. In addition, we examined whether NiCrMnSi Heulser phase lms can be obtained by a magnetron sputtering on MgO substrates. The results of the structural analysis and rst-principles calculations indicated that NiCrMnSi Heusler phase is metastable. A possible route to obtain metastable NiCrMnSi Heusler alloy is to utilize appropriate templates
Magnetic tunnel junctions with a B2-ordered CoFeCrAl equiatomic Heusler alloy
The equiatomic quaternary Heusler alloy CoFeCrAl is a candidate material for spin-gapless semiconductors (SGSs). However, to date, there have been no experimental attempts at fabricating a junction device. This paper reports a fully epitaxial (001)-oriented MgO barrier magnetic tunnel junction (MTJ) with CoFeCrAl electrodes grown on a Cr buffer. X-ray and electron diffraction measurements show that the (001) CoFeCrAl electrode films with atomically flat surfaces have a B2-ordered phase. The saturation magnetization is 380 emu/cm3, almost the same as the value given by the Slater–Pauling–like rule, and the maximum tunnel magnetoresistance ratios at 300 K and 10 K are 87% and 165%, respectively. Cross-sectional electron diffraction analysis shows that the MTJs have MgO interfaces with fewer dislocations. The temperature- and bias-voltage dependence of the transport measurements indicates magnon-induced inelastic electron tunneling overlapping with the coherent electron tunneling. X-ray magnetic circular dichroism (XMCD) measurements show a ferromagnetic arrangement of the Co and Fe magnetic moments of B2-ordered CoFeCrAl, in contrast to the ferrimagnetic arrangement predicted for the Y -ordered state possessing SGS characteristics. Ab-initio calculations taking account of the Cr-Fe swap disorder qualitatively explain the XMCD results. Finally, the effect of the Cr-Fe swap disorder on the ability for electronic states to allow coherent electron tunneling is discussed