Preparation and magnetic properties of Fe100−xNix-SiO2 granular alloy solid using a sol-gel method

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_!Sg 2

A

journal 01 magnetism

IH A

t&etic materials

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2

ELSE\ IER

Letter to the Editor

Preparation

and magnetic properties of Fe,,:,,:,_,Ni ,-SiO, alloy solid using a sol-gel method

Nei-Fai

Gao. Yuan-Yuan

granular -

Liu

Abstract The preparation means oi S-ra) 3110) parttck

of Fe ,,“.,_,

dlfiractron dtspcrwd

in Fe-50..

are confwmcd h) ths rewlt thr: FetiiNi,-,-SIOI wperparamapnctrim.

Nanocomposite

studied

esterGel)

NI ,-SIO: 1.1= 0. 20. hl:L ?W)granular wltd urine 3 sol-gel method

and kctron

transmksron Fc,,NI,,-SIO,

oi the .
and F~y,,Nli,-,-SiO, single-domain

mIcrograph\.

and Fe::,,Nr,,,-SiO,

and the hltissbaucr granular

SolId during

and multldomrlin

materials

have

because

of their

recentI! potential

txen us?

itc material consisting of ultrafine m
wlid with imestigated

a 4nglc more in

the past. Recently. tht fabricatton and phlsiccll properties of the granular alloy solid has rewiled more attention bccauw alloys hair: almost rlh\a)s prwrn IO lx more useful and tnterssttng than their pure metallic c’otwttuents [l-h]. Espe-

spectrums. Awing

granulnr

IS

tmcrtlpated

and Fe,,Ni,,,

SolId hate been tahricated rrhlch

The e\oIutron oi the magnetI< propertIes tire decrrhed

b!

ultraiine for

In detail and ?\plaincd b\ uclng

thcon.

in technolom. such as high densin magnetic recording medium. ferrollutds. catalysts and so on. Granular metal soltd is a type of nanocompos-

proprrttss elemental

Pure Fe metal. Fc..,Nl,,,

ciall!, for Fe, _, Ni, alloy. the imar .W? nickel and the order-disorder

problem for transforma-

tion for FeNi? [7.X] are \trlI-kknwn. However the method of granular alloy solid IS mainly cosputwing and mechanical ball mising. Among the karict?; of means to prepare nanocompostte mat+ rtal. a sol-gel method effectike and economical

has already proken ~a! of fabrication

an [9-

II]. bum studies on the preparation and magtwtic proptzrticc oi granular alloy solid are farer In this paper. we ha\e wccrl~sfull~ prepared Fe !,,,,_, Ni , -SiO, granular allo! solid using ;1 WIgel method. uhich has been car
.:

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,yr ..L

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._.-. ;.. .. ..

:;

:;

‘...

‘f’

.

..-. .._

.

. \

:

i 1 ~~~~~~ .

-12

-8

-4 Velocity

The magnetic propertiss oi th< Fe,,,,,_, SIO, granular solid here ;lre imrstigatrd. sarurcrlion

magnetization

aI room

remperature

NI

,-

Ths of

grnnular solid F~,,_,NI,,,- SiO, and Fe:,,-,Ni.,,-50, ierrus redwing rrlmperature I T, b is shwn in Fig. 5. The magnrltization oi rhee samples incwaw

with the increase oi T<. The degrsc oi rhls incrcse ior the Fe,,-,NI,,,,-SiO. %:rrnple\ is larger than rhat ior the Fe,,,Ni,,,,-SIO, sampler;. The srlluration magnstlzarion ot the allo! partic’le in the F?,,,NI, ,,.,-SiO. snd Fc,,,NI.,,-SiOprdnulur solid reaches 13.3 and 105 emu g r
;1re \tl~ near to the values ol’ hulli Fe,,,Ni,,, Fe,,,Nl.,, allo) \rhich are 1-l: and 3h emu g respectwctl! .[13]. Her? the orrginol allo! particles

and

conwnrr~rion 1W (k\\cighrr in grsnulsr solid is used to calculate rhc allo) mapnetlzation In fact. the real allo) wncentra[ion in the granular solid 15 ken near to the orlplnal one It is knwn thvr [he a\erape six oi Ihe allo> particles Increysc< \trth the increase of the redwIng tempercrrurr: and [hers IS a irids rungs of kc‘ distribution c-ri the allo! parrlcles irom the TEhl mvxopraphs nt’ these granular 3llo! solid samples So. the proportron ol the sup
.

G

-1 pn

z;ltron of rhese Fe,,,-,_, Ni,-SIO, solid sample \rlth thr: Incrrttise tcmpersture.

8

12

‘5)

granular allo! of the reducing

FsNi

410~ particles

of the

is

or&r

oi a couple

oi

tens of nm. the precise value depending on the shape oi the particle [ 141. This sInpIe-domain configuration causes ultrafine allo! particle5 lo exhibit much larger magnetic c’oercnlties rhan

that oi bulk allo). The decrease of ihe c‘oerciviI> ior rhe granular alloy solid samples rcduwd at 7, c SOWC ma! lx caused b! the increase oi rhe

proportion oi the superpsramagnetic allo) particles in the granular solid \\hich she\\ the superparamagnetlc rela\atlon and hai< The decrease oi the coer
zero cocrcn 111 for the granu-

lar

at

[I-I].

alloy

solid


reduced

about

T,

”

W(r’C ma)’ lx caused b> the increase of rhe proportion of the all01 partlcle‘i \\rlth multido-

“400

450

500

550

TEMPERATURE FIN. 6. Ctwra\In lure

tar

rhc

\s. rrducing Fe,,,Nl,,,-SO.

700

SiO,

FCI

Iempcr3turc and

650

600

main which ma! cause the soft magnetic properties with smaller coercivitp. In conclusion. in this \\ork. Fe-SIO, granular metal solid and Fe,,,Ni,,-SiO, and Fe,,-,Ni,,-,-

81 room Iempcre.

Fe:,:,Nl.,, -WI!

franulsr

solid samples

granular

alloy

solid

in \rhiih

iron metal

and

Fc,,,Ni,,-, and Fe:,,Ni.,, allo) partlclcs are dispersed in the SIO, ma.trl\ hats heen successiull> fabricated using a sol-gel method. The magnstizatlon and the coercikio of the granular allo! solid vs. the reducing temperature are inwsti-

The coercivib at room tempsrarure of the Fs,,jNi,,-Si02 and Fe2,:,Ni5,:,-SiOT granular solid versus the reducing temperature IS shown in Fig. h. The coerci\Itp of the Fe,,:,Ni,,,,-SiOgranular solid samples is about two times-high& than that of the Fe.,,Ni,,,-SiOgranular solid samples. This may he caused by the higher magnerir anisorrop) constant of Fe,,:,Ni,,?-, ‘GO, than that of Fe,,,Ni.,, -SiO, because the magnsrocrystalline constant is near zero and the magnelostriciion is \en small for F:,!Ni,,, allo) comparing with F~,,:,NI,,:, allo). The coer&lry varied with the reducing temperalure (7,) for both rhe Fe,,,Ni,,-SiOand Fe2,,Nib,:,-SiO: granular solid samples and-sho\\s a ma_timum Lalue at about T, = 5OO’C although iI is not wn obvious for the Fe,,,Ni,,,-SiO, granular solid samples. This is because the proportion of the thermal slahle single-domain allo) parriclss is highest for the Fe.,Ni,,,,-SI07 and Fc,,,Nl.,,SiO, granular solid samples riduced at about T( = WWC. II is well knonn that the critical size for [he formation

ofa

single

magnctlc

domain

in

gated. Supsrparsmagnetism. single-domain and mullidomain thcop are used 10 csplaln ihs experimentul results.

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~,J

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