Site-specific order and magnetism in tetragonal Mn3Ga thin films

Abstract

Mn

3

Ga bulk material and thin films deposited on several different substrates have been investigated using

x-ray and neutron diffraction, x-ray absorption spectroscopy, x-ray magnetic circular dichroism, and electronic

structure calculations using density-functional theory with the aim of determining the atomic site occupancy,

magnetic moments, and magnetic structure of this tetragonal D0

22

-structure compound. The Mn

3

Ga has close

to ideal site occupancy, with Ga on 2

a

sites and Mn on 2

b

and 4

d

sites. The magnetic structure is basically

ferrimagnetic, with the larger Mn moment of about 3

e_

B

on the 2

b

site, which is coordinated by 8 Mn 4

d

and

4 Ga, and the smaller one on the 4

d

site, which is coordinated by 4 Mn 2

b

, 4 Ga, and 4 Mn 4

d

.TheMn

d

-band

occupancy is close to 5 on both sites, and the orbital moments are small,

<

0

.

2

e_

B

. The material nevertheless

exhibits substantial uniaxial anisotropy,

K

u

=

1

.

0MJm

?o?

3

, which originates from the 4

d

site. The 2

b

site has hard

axis anisotropy, which together with an oscillatory exchange coupling from the first and second nearest neighbors,

leads to a soft component of the magnetization in the

c

plane, coexisting with

c

-axis hysteresis loops exhibiting

coercivity of up to 1.2 T, and magnetization in the range 110?UO220 kA m

?o?

1

at room temperature, depending on

preparation conditions. Tetragonal Mn

2

Ga films behave similarly. Manganese is lost from both sites, but the films

have substantially larger magnetization (480 kA m

?o?

1

) and anisotropy constant (2.35 MJ m

?o?

3

)thanMn

3

Ga.