((()(()((((((    
Zinc blende structure

Shirai et al. predicted zinc-blende CrAs is half-metallic ferromagnet
From first-principles calculations. Akinaga et al. confirmed
this prediction experimentally later.
(Jpn. J. Appl. Phys. 39 (2000) L1118)

DOS   
Up spin Metallic DOSEnergy
Down spin

Insulating DOS

100 % spin polarization at the Fermi level.
Expected as a spin polarizer for semiconductor spintronics.

       1. CrAs
 DOS, magnetic moment, half-metallicity, TC
2. With transition metals other than Cr (such as V, Mn …)
3. With anions other than As (such as N, P, Sb, S, Se, Te …)
4. How large TC values are expected ?
5. Lattice constant dependence ?
 Suppose different substrate Calculate theoretical lattice constant. Half-metallic ?

)(-(((()-(-()())-- 
Composed with FCC sub-lattices(similar to the zinc blende structure)

Full Heusler
Co2MnSi …
Half-metallic, TC=985 K
Half Heusler
NiMnSb (a = 5.93 Å)
Half-metallic, TC=730 K
Various combinations of transition metals.
Systematic study on the electronic structure, magnetic moment, TC     

1. NiMnSbCoMnSbFeMnSb
 DOS, magnetic moment, half-metallicity
 Estimate TC
2. Magnetic moment vs. total valence electron number
 Slater-Pauling curve, Guess how large magnetic moment is expected for different
combinations
 Confirm the above expectation by ab-initio calculation.
 Is it also true in ,e.g., (Ni1-xCox)MnSb ?
3. New ferromagnets based on semiconducting Half-Heusler alloy Predict semiconducting Half-Heusler alloy based on the Dope magnetic impurities Co(Ti, Mn)Sb)() )()Schematic density of state of half-Heusler alloy
18 electrons are needed
to fill up the valence band
Sb-5s
NiMnSb
Valence electrons
Sb: 5
Ni: 10
Mn: 7
Total: 22

Mn-3d

Sb-5p
1

35

1

354Energy

Ni-3d
Fermi Energy
Magnetic moment= total valence electron number – 18=22-18 = 4          • Dilute magnetic
semiconductors (DMS)(Ga, Mn)As••••(Ga, Mn)As, (In, Mn)As ..
Ferromagnetic material
Ferromagnetism controllable
by changing carrier density
Semiconductor spintronics• High-Tc DMS necessary•High concentration dopingcrucial• Material design
H. Akai,Ohno PRL
et al. 81
JMMM(1999) 110.
(1998)2003002
Nature 408 (2000) 944. Nature 402 (1999) 790.

Masek et al., PRL 98 (2007) 067202++)

Mahadevan et al., PRB 68 (2003) 075202.

()

Juza et al., Angew. Chem. 7 (1968) 360
v. G. Achenbach et al., Z. Anorg. Allg. Chem. 476 (1981) 9.

()))(( (,()()((( ()).

(((   Z. Deng et al., Nature Commun.
2:422, (2011, Aug.) 1-5.

Solid-state reaction
XRD
dc-magnetization, µSR
Hall effect ⇒ p-type
Li at Zn substitutionalsite   
    

DOS↑(EF ) − DOS↓(EF )Polarization =DOS↑(EF ) + DOS↓(EF )        

DOS↑(EF ) − DOS↓(EF )Polarization =DOS↑(EF ) + DOS↓(EF )     

DOS↑(EF ) − DOS↓(EF )Polarization =DOS↑(EF ) + DOS↓(EF )1. Rechargeable battery• Chargeable, usable repeatedly• Lead battery, Ni-Cd battery• Li-ion battery, Ni-H battery (large energy density

Design of positive andnegative electrodes
for more effective
rechargeable battery       
A. ‘good’ battery
1. High voltage
2. Large capacity
3. Low cost
4. Light weight
5. safety
Positive electrode
CoO2 + Li + + e− → LiCoO2
Negative electrode
Li → Li + + e−€
Totaldischarging reaction CoO2 + Li → LiCoO2    1. Estimation ofbattery voltage
2. Negativeelectrode Li metal
3. No lattice relaxation
Rhombohedral
R (TM): (0,0,0)
M (Li): (1/2, ½, ½)
O: (u, u,u), (-u, -u, -u)−V = TE(LiCoO2 ) − TE(CoO2 ) − TE(Li)    Co is very expensive → use the other transition metals for electrodes

TiVCrMnFeCoNi¥/kg 2000 6000

40031030-90 80002000

toxicity

l Chemical trend of the battery voltage on TM ions
LiTMO2, TM=Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Al
l Alloying works? Use much cheaper TM metals
Li(Co, Al)O2, Li(Co, Zn)O2, Li(Co, Cu)O2
Li(Ni, Mn)O2
Li(Ni, Mn, Co)O2)(())))

TM conc. = 10 %,100%)

Suppose u=0.26

Hydrogen energy system•Decomposition of H2O by using solar energy → H2
•Energy storage and transfer in the form of H2•Taking out electricity by using fuel cell→ ‘Greener’ energy cycle→Hydrogen strage material) %%))Metal hydrates (inorganic hydrogen storage materials)
9C7 .
•High H concentration- /8HJ.
•Low price•Too stable 62
4F -5D1.
)-%%%%-%.

→Un-stabilize the metal hydrates by doping transition metal impurities

M. Tsuda et al., Thin Solid Films 509 (2006) 157

      

ΔE = TE(MgH 2 : rutile) − TE(Mg : hcp) − 2 × TE(H)1. Instead of TE(H2 molecule), we use TE(H: FCC) to bein consistent with MT approximaion.
TE(H)=-1.076 Ry
2. Lattice constants of MgH2, Mg → experimental value
3. No-lattice relaxation• Calculate how largely we can destabilize MgH2 byintroducing transition metal impurities.
• Which TM is the most effective ?
MgH 

a= 4.501 A,
c=3.01 A,
u= 0.304Mg
a= 3.20936 A,
c=5.2112A,

(((() ((ΔE = TE(Mg1−x TM x H 2 : rutile)−TE(Mg1−x TM x : hcp) − 2 × TE(H)€D

1. Calculate DE, when transition metal impurity TM(TM=Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn,) are dopedin MgH2. Suppose x=0.1
ΔE(MgH 2 ) = −1.376eV)€By using the CPA, all phases (disordered, ordered)can be calcuated with in the same framework.

       

Assumption:
Lttice constants follow the Vegard’s law.

x = 25, 50, 75 %a(A1−x Bx ) = (1− x) × a(A) + x × a(B) SCST
Pt: (0, 0, 0)
Pt: (0, 0, 0),
Fe: (1/2, ½, 0),(1/2, ½, 0),(1/2, 0, ½),
Fe: (1/2, 0, ½),(0, ½, ½)(0, ½, ½)
Assumption:
Lttice constants follow the Vegard’s law.

 SC
Fe: (0, 0, 0)
Pt: (1/2, ½, 0),(1/2, 0, ½),(0, ½, ½)a(A1−x Bx ) = (1− x) × a(A) + x × a(B)