J. Magn. Soc. Jpn., 41, 127-131 (2017)<Paper>ofSynthesis and Magnetic Properties
Substituted W-type and Y-type Ferrites(Zn 2+ Ti 4+ )K. Watanabe, K. Kakizaki, and K. Kamishima
Graduate School of Science and Engineering, Saitama University, 255 Shimo-Okubo, Sakura-ku, Saitama 338-8570, Japan

We report the synthesis of (Zn2+Ti4+) substituted hexagonal ferrites, BaZn2(Zn0.5Ti0.5)xFe16-xO27 (W-type) and
Ba2Zn2(Zn0.5Ti0.5)xFe12-xO22 (Y-type), and the relationship between their composition and magnetic properties.
Substituted W-type ferrite was synthesized in the region of 0.0 ≤ x ≤ 1.5. A decrease in the Curie temperature of theW-type phase indicated that the exchange interactions between the Fe3+ ions weakened due to the substitution of Zn2+
and Ti4+ ions. Spontaneous magnetization (σS) at x = 0.5 was similar to that at x = 0.0. This reflects the equal
distribution of nonmagnetic Zn2+ and Ti4+ ions to spin down sites and spin up sites, respectively. At x > 0.5, σS
decreased clearly, which was possibly caused by a deviation from the collinear arrangement. Substituted Y-typeferrite was also obtained up to x = 0.5. The Y-type phase is more unstable than the W-type phase with respect to thissubstitution rate.
Key words: W-type ferrite, Y-type ferrite, (ZnTi) substitution, solid state reaction, X-ray diffraction,
Curie temperature, spontaneous magnetization, cation distribution
1. Introduction
The hexagonal ferrites have been investigated forelectronic devices at microwave frequencies since theirdiscovery in 1950s 1). Their availability at highfrequencies is caused by the large magnetic anisotropy
constants and the preference to several magnetized
directions, parallel or perpendicular to the hexagonal
c-axis. Most of ferrites also have low eddy current loss athigh frequency and corrosive resistance because they areoxides.
The crystal structure of hexagonal ferrites is based
upon the close-packed structure of large oxygen anions
and barium cations. The small transition metal cations(Fe3+ and Me2+) are located between the larger ions. The
structures of hexagonal ferrites can be represented by
the stacking combinations along their hexagonal c-axisof R, S, and T blocks 2). The chemical formulae for theseblocks are as follows: R = (BaFe6O11)2-, S = Me2Fe4O8 /(Fe6O8)2+, T = Ba2Fe8O14. The composition of the S block
corresponds with the two formula units of the spinel
ferrite. The major hexagonal ferrites are described by
the following symbols: RSR*S* for M-type (BaFe12O19),(RSR*S*S*)3 for X-type (Ba2Me2Fe28O46), RSSR*S*S* forW-type(BaMe2Fe16O27),
(TS)3
for
Y-type(Ba2Me2Fe12O22),
RSTSR*S*T*S*for
Z-type(Ba3Me2Fe24O41),
and(RSTSR*S*)3for
U-type(Ba4Me2Fe36O60) 3), 4). The superscript * denotes that thelayer is turned for 180° around the c-axis.
M-type barium ferrite (BaFe12O19) is widely used forpermanent magnets due to its large magneto-crystalline
anisotropy 5). In addition, many research groups haveinvestigated barium ferrite as microwave absorbers 6)-8)
and magnetic recording media 9) by modifying its
anisotropy. The control of its magnetic property isachieved by the replacement of Fe3+ ions by Al3+ 10)-13),

Cr3+ 13)-15) ions or pairs of (Me2+Mt4+) ions such as(Co2+Ti4+) 16, 17), (Zn2+Ti4+) 18), 19), (Mn2+Ti4+) 6), 20),
(Ni2+Sn4+) 21), (Co2+Sn4+) 22), (Co2+Zr4+) 23), 24), where the
Me and Mt represent divalent and tetravalent cations,
respectively. The substitution effect on anisotropy is sosignificant that even the hard magnetic property of
BaFe12O19 was changed to soft magnetic by substitutionof (Co2+Zn2+)Ti4+ for Fe3+ 25).
On the other hand, W-type and Y-type ferrites havedifferent magnetic properties from those of M-typeferrite due to their different stacking structures. W-typeferrite can possess higher saturation magnetization thanthat of M-type ferrite 26). Y-type ferrite has planar
anisotropy 27), which gives hope for high-frequency
application. Therefore, the control of the magnetic
properties of W-type and Y-type ferrites has been an
important issue.
To the best of our knowledge, however, there are few
investigations on the substituted W-type and Y-typeferrite. Maeda et al. reported the preparation by aconventional ceramic technique, magnetic properties,
and microwave absorption properties of the (Mn2+Sn4+)
and (Mn2+Zr4+) substituted W-type ferrite 28). Ul-ain et al.
reported the synthesis by sol-gel method and catalytic
activities of the (Mn2+Ti4+) substituted Y-type ferrite 29).
Also, substitution limits of Me2+Mt4+ for Fe3+ in W-type
and Y-type structures are unclear in contrast with thatin the M-type structure where complete substitution of
Co2+Ti4+ for Fe3+ is possible to form BaCo6Ti6O19 30).
We report the synthesis of the (Zn2+Ti4+) substituted
hexagonal ferrites, BaZn2(Zn0.5Ti0.5)xFe16-xO27 (W-type)
and Ba2Zn2(Zn0.5Ti0.5)xFe12-xO22 (Y-type), and the relation
between their composition and magnetic properties inthis paper. Here, we employed Zn2+Ti4+ cations for
substitution because an increase of the magnetization
was expected if nonmagnetic cations replaced Fe cations

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in spin down sublattices as observed in substituted
spinels 31).
2. Experimental procedure
The samples were prepared by solid-state reaction. We
used BaCO3, ZnO, TiO2, and α-Fe2O3 as starting
materials. They were mixed in the desired composition of
Ba : Zn : (Zn0.5Ti0.5) : Fe = 1 : 2 : x : (16-x) for the W-typeferrite and Ba : Zn : (Zn0.5Ti0.5) : Fe = 2 : 2 : x : (12-x) for
the Y-type ferrite with 0.0 ≤ x ≤ 2.0 in a ball-milling pot
for 24 h. The mixed powders were pressed into disks andthen pre-sintered at 900°C in air for 5 h. The products
were ground in a mortar and then pulverized for 10 min.
at the rate of 1100 r.p.m. in a vario-planetary mill. The
fine powders were pressed into disks again and thensintered at 1100-1350°C in air for 5 h. Finally, theproducts were ground into powders in a mortar.
The crystal structures were examined by powder X-ray
diffraction (XRD) with Cu-Kα radiation. The
magnetizations were measured with a vibrating sample
magnetometer (VSM), and a superconducting quantum
interference device magnetometer (SQUID).

sintered at 1250°C, provided that the W-type phase was
the minority phase for the sample with x = 1.5. The
samples with 0.0 ≤ x ≤ 1.5 sintered at 1300°C and 1350°C
consisted of the main W-type phase. On the other hand,at sintering temperature of 1350°C, the sample
contained the M-type and spinel minority phases. Since
this temperature is near to the melting point of the otherbarium-iron oxides (e. g. Ba2Fe2O5; Tm = 1370°C 32)), theW-type phase is likely to decompose. These results showthat the sintering temperature of 1300°C is the suitablecondition for the synthesis of the substituted W-typeferrites.
Fig. 2 shows XRD patterns of W-type composition
samples with Ba : Zn : (Zn0.5Ti0.5) : Fe = 1 : 2 : x : (16-x)
sintered at 1300°C. The samples had the W-type
structure at 0.0 ≤ x ≤ 1.5. At x = 1.5, there were some

3. Results and discussion
We identified the crystalline phases of the W-type
composition samples with 0.0 ≤ x ≤ 2.0 sintered at
1200-1350°C by XRD. Fig. 1 shows phase relationshipbetween sintering temperature and substitution rate x.
At 0.0 ≤ x ≤ 1.5, the W-type phase formed in the samples
Fig. 2 XRD patterns for products sintered at
1300°C whose raw materials were mixed incomposition of Ba : Zn : (Zn0.5Ti0.5) : Fe = 1 : 2 : x :(16-x) with 0.0 ≤ x ≤ 2.0.

Fig. 1 Relationship between obtained crystalline
phase and sintering temperature and substitution
rate x for samples whose raw materials were mixed
in composition of Ba : Zn : (Zn0.5Ti0.5) : Fe = 1 : 2 : x :(16-x) with 0.0 ≤ x ≤ 2.0. Phases in parentheses areminority phases.

128

Fig. 3 XRD patterns for products sintered at
1100°C whose raw materials were mixed incomposition of Ba : Zn : (Zn0.5Ti0.5) : Fe = 2 : 2 : x :(12-x) with 0.0 ≤ x ≤ 2.0.

Journal of the Magnetics Society of Japan Vol.41, No.6, 2017

weak diffraction peaks of the M-type and spinel ferrites.
On the contrary, the peaks of the W-type phase
disappeared in the pattern at x = 2.0. It should be notedthat the first and second peaks of the W-type phase do
not overlap those of the spinel and M-type phases ascomparing the patterns between x ≤ 1.5 and x = 2.0. Fig.
3 shows XRD patterns of Y-type composition samples
with Ba : Zn : (Zn0.5Ti0.5) : Fe = 2 : 2 : x : (12-x) sintered at
1100°C. We obtained the Y-type phase in the samples
with x = 0.0 and 0.5. On the other hand, the diffraction
peaks of the Y-type phase weakened at x ≥ 1.0 andfinally disappeared at x = 2.0. The phase identification
was based on the diagrams of the BaO-ZnO-Fe2O3 33),
BaO-ZnO-TiO2 34) and BaO-Fe2O3-TiO2 35) systems,
which showed no corresponding compounds except forthe spinel and Y-type phases. The maximum
substitution rate of (ZnTi)/(Fe+(ZnTi)) to form the single
Y-type phase (0.5/12 ~ 4.2%) is smaller than that to form
the single W-type phase (1.0/16 ~ 6.3%). Therefore, theY-type phase is less stable than the W-type phase for(Zn2+Ti4+) substitution.

between Fe3+ ions weakened. This fact implies that Zn2+
and Ti4+ cations successfully replaced Fe3+ cations in theW-type structure at x ≤ 1.5.
Fig. 5 shows magnetization curves at T = 5 K (= –268°C) for W-type samples of BaZn2(Zn0.5Ti0.5)xFe16-xO27(0.0 ≤ x ≤ 1.5) sintered at 1300°C. The magnetization
curve of the substituted samples at x = 0.5 was almost
the same as that of the no-substitution sample (x = 0.0).
Then, the magnetization decreased with increasing thesubstitution rate from x = 0.5 up to 1.5. This result is
consistent with the fact that M-type ferrite showedsimilar Zn-Ti substitution dependence of spontaneous
magnetization 37), where the magnetization began toFig. 5 Magnetization curves at T = 5 K (= –268°C)
for samples sintered at 1300°C whose raw materials
were
mixed
in
compositionof
BaZn2(Zn0.5Ti0.5)xFe16-xO27 with 0.0 ≤ x ≤ 1.5.

Fig. 4 Temperature dependences of magnetization
at µ0H = 0.1 T for samples sintered at 1300°C whose
raw materials were mixed in composition of
BaZn2(Zn0.5Ti0.5)xFe16-xO27 with 0.0 ≤ x ≤ 1.5. Inset
shows Curie temperatures TC of those samples.
Fig.
4
shows
temperaturedependencesofmagnetization at µ0H = 0.1 T for W-type composition
samples of BaZn2(Zn0.5Ti0.5)xFe16-xO27 (0.0 ≤ x ≤ 1.5)
sintered at 1300°C. Inset of Fig. 4 shows the Curie
temperature TC of the W-type phase as a function of thecomposition x, where TC was estimated by linear
extrapolation to zero-magnetization from the inflection
point of the M-T curve. The Curie temperature TC of the
no-substitution sample (x = 0.0) was 305°C, which is inagreement with the previous report about BaZn2Fe16O27
single crystals 36). TC linearly decreased with increasingx at x ≤ 1.5, suggesting the exchange interactions

Fig. 6 Spontaneous magnetization and high field
differential susceptibility for samples sintered at
1300°C whose raw materials were mixed incomposition of BaZn2(Zn 0.5Ti0.5)xFe16-xO27 with 0.0 ≤ x≤ 1.5.

Journal of the Magnetics Society of Japan Vol.41, No.6, 2017129

decrease above a certain Zn-Ti substitution rate.
Fig. 6 shows spontaneous magnetization σS and highfield differential susceptibility χd as a function of thecomposition x. They were estimated by linear
extrapolation of the magnetization curves from a highfield region. The spontaneous magnetization σS slightly
decreased from x = 0.0 to 0.5. In the range of 0.5 < x ≤ 1.5,
the decrease of σS became more obvious. The
substitution effect on σS seems to reflect Zn2+-Ti4+ cation
distribution in the W-type structure.
In order to discuss the relationship between the change
in σS and the cation distribution in the W-type structure,
we consider the spin configuration of the W-type
structure. Table 1 shows the distribution of thetransition metal sites and the expected directions of themagnetic moments in the R and S blocks of the W-type
structure 38). Fig. 7 also shows magnetic structure of
W-type ferrite, corresponding to Table 1.
Concerning the cation distribution in the W-type
structure, we assume that the Zn2+ ions prefer the 4e
and 4fIV sites and that Ti4+ ions prefer the 12k sites. In
the case of the (ZnTi) substituted M-type ferrite 37), Zn2+
ions tend to enter the tetrahedral 4fIV sites in the S block.
Also, Ti4+ ions tend to enter the octahedral 4fVI (the R
block) sites and the 12k (the S and R blocks border) sites.
In our W-type ferrite case, even with no substitution
sample of x = 0.0, however, the positively charged part of
two S blocks of (Zn2Fe10O16)2+ and the negatively charged
R block of (BaFe6O11)2- are alternately stacked up as
SSRS*S*R*. The additional Zn2+ ions seem to occupy 4eand 4fIV sites in the S blocks like the ZnTi-doped M-typeferrite. In order to keep the local electronic balance inthe additional Zn2+ doped S blocks, Ti4+ ions may prefer
the 12k sites to the 4fVI sites because of the proximity to
the Zn2+ sites in the S block.
We discuss the effect of the nonmagnetic ions upon the
spontaneous magnetization σS depending on x. Between
x = 0.0 and 0.5, the occupation of spin down (4e and 4fIV)  sites by Zn2+ ions can be cancelled out by the occupationof spin up (12k) sites by Ti4+ ions. Therefore, thedecrease of σS is slight in this range. At x > 0.5, theobvious decrease of σS is possibly caused by the deviationfrom the collinear arrangement which can be dominant
at high substitution rates of Zn2+ and Ti4+ ions 37). To
ascertain our estimation, further experimental
investigations are needed to estimate the spin
configuration and the cation distribution by Rietveld
analysis on powder neutron diffraction 39) and X-ray
absorption fine structure analysis 40).
The high field differential susceptibility χd for thesubstituted W-type ferrite increases with increasing x as
shown in Fig. 6. It suggests that the magnetic structureof the substituted W-type ferrite becomes non-collinear
especially at x > 0.5. It is consistent with theinterpretation of the variation in σS discussed above.

130

Table 1 Coordination, number of ions, and spinorientation for various cation sublattices of W-typeferrite.
Block

Sublattice

Coordination

Number
per
block

Spin

S-S

6g

Octahedral

3

Up

S

4e

Tetrahedral

2

Down

S

4f

Octahedral

2

Up

S

4fIV

Tetrahedral

2

Down

S-R

12k

Octahedral

6

Up

R

4fVI

Octahedral

2

Down

2d

Trigonal-bipyramidal

1

Up

R

Fig. 7 Magnetic structure in half of unit cell (informula unit ) of W-type ferrite.
4. Conclusions
We report the synthesis condition and the magnetic
properties of the (Zn2+Ti4+)-substituted W-type andY-type hexagonal ferrites that have hardly been
investigated so far. The synthesis condition shows thesubstitution limits of Zn2+Ti4+ for Fe3+ in the W-type andY-type ferrites, suggesting the stability of the W-type
and Y-type structures.
The W-type composition samples sintered at 1300°C
had the W-type structure in the region of 0.0 ≤ x ≤ 1.5.
The Curie temperature of the W-type phase decreased
linearly with increasing x at x ≤ 1.5. It suggests that theexchange interactions between the Fe3+ ions weakened
due to the substitution of nonmagnetic Zn2+ and Ti4+ ionsin the W-type structure. Spontaneous magnetization σS

Journal of the Magnetics Society of Japan Vol.41, No.6, 2017

at x = 0.5 was similar to that at x = 0.0. It reflects theequal distribution of nonmagnetic Zn2+ and Ti4+ ions tospin down sites and spin up sites, respectively. At x > 0.5,
σS decreased clearly, which is possibly caused by thedeviation from the collinear arrangement. It isconsistent with the increase in the high field differential
susceptibility χd with x.
The Y-type single phase was also obtained for the
Y-type composition samples up to x = 0.5. The Y-typephase is more unstable than the W-type phase withrespect to this substitution rate.
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Received Jul. 20, 2017; Revised Sept. 3, 2017; Accepted
Sept. 19, 2017

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