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We report the results of a rigorous calculation on the total internal reflection when the second medium is absorbing. A complex dielectric constant given by, \(\hat{\varepsilon }^{\text{Re}} + i\ha...

The magnetization process of a single crystal of the spin (S) one linear-chain Heisenberg antiferromagnet, Ni(C2HsN2)2N02(ClO.), under very high magnetic field has been measured. The magnetization is very small in the low-field region and begins to increase sharply at a finite field for all three of the principal axes. The transition field (HT) above which the system becomes magnetic depends on the direction of the applied field. These experimental results are consistent with the picture that (i) the ground state of S = 1linear chain Heisenberg antiferromagnet is a singlet and (ii) the system becomes magnetic above HT due to closing of the quantum energy gap. The experimental results are analyzed based on a simple energy level scheme. The anisotropy in HT is successfully explained by the theory using the following parameters; the Haldane gap energy EG=17 K and the single ion anisotropy constant IDI=16 K. These values of EG and D are close to those obtained from other experiments. Using the theory developed in analyzing the magnetization data, we can also explain the behavior of the excitation spectrum of this compound in external magnetic fields determined from the neutron inelastic scattering experiment.

The results of a rigorous calculation of optical phenomena in absorbing media based on Maxwell’s equations are reported. In the case of an absorbing dielectric, we assume a complex dielectric const...

Non-resonant x-ray scattering experiments on CeB6 under applied uniaxial pressure and magnetic field have been performed. Measurements of different orbital superlattice reflections show different temperature dependences. The changes in the scattered x-ray intensity as a function of applied pressure and field can be interpreted as being due to the change in the orientation of the 4f orbitals.

X-ray diffraction studies have been performed up to 38 T in conjunction with synchrotron x-ray beams and a split-pair pulse magnet at the beamline BL19LXU of SPring-8. The magnet consists of coaxial two-coils which are made by winding CuAg wire up to 18 layers. The magnet has four windows with wide aperture angles and the height of 3 mm for passage of the x-ray beam. A pixel array detector was used to measure the diffraction patterns during an exposure of 5 millisecond around the peak field. The details of the instrumentations are presented.

Magnetic susceptibility, magnetization and heat capacity measurements are made on a single crystal sample of a spin–ladder material, Na 2 Fe 2 (C 2 O 4 ) 3 (H 2 O) 2 . The susceptibilities show a b...

Results of non-resonant X-ray Bragg diffraction measurements in the phase II of CeB 6 under an applied magnetic field, H , are reported. The intensity of the superlattice reflection ( n /2, n /2, n /2) increases dramatically with H applied along the [111] axis, where n is odd. On the other hand, the superlattice intensity decreases with H along the [\bar211] axis normal to the scattering vector. These behaviors of the superlattice intensity in H are explained qualitatively by the combined effects of the magnetic moments tending to align parallel to H and the spin orbit coupling which tends to align the extended wave function of the f electron normal to H . Using this relation, one can manipulate the multipole moments in rare-earth compounds by magnetic fields.

The magnetic structures of the low-carrier-system CeP are investigated under magnetic fields up to 12.5 T with the field H ∥[1 \bar1 0] and up to 14 T with H ∥[0 0 1] by synchrotron X-ray diffraction utilizing the unique relationship between the magnetic structure and lattice modulation in this system. The magnetic phases corresponding to the modulation wave vectors k =2/11, 2/10, 2/9 and 2/8 are observed at low temperatures. The magnetic phases with k =2/8 (↑↑°°°°°° or ↑↑←→←→←→), k =2/9 (↑↑°°°°°°° or ↑↑←→←→←→←) and k =2/11 (↑↑°°°°°°°°°) are the new phases under magnetic fields found in the present work. The result demonstrates that magnetic fields play a role similar to high pressure to realize the unique magnetic structure and its multistep change in CeP. This fact indicates the importance of the magnetic polaron effect mediated by the p – f mixing effect in the system.

X-ray diffraction measurements on α-solid oxygen under an applied magnetic field are reported. The volume of α-solid O2 is found to expand with increasing magnetic field: the lattice constants a and b elongate, while the lattice constant c and the angle β are almost independent of the magnetic field. The maximum volume expansion observed is about 1% under a 7.5 T field, which is a giant effect compared to the volume change observed in ferromagnetic metals, such as Fe, Co and Ni. This finding indicates that a spin-dependent inter-molecular potential is essential in determining the structure of α-solid O2. The experimental results conform with predictions based on a magneto-elastic interaction derived from an antiferromagnetic exchange coupling of O2 spins.

Neutron diffraction measurements on a powder sample of α- 160 Gd 2 S 3 are performed. This material consists of a stacking of square lattice Gd1 and triangular Gd2 planes and exhibits a novel phase transition that was interpreted as being due to geometrical frustration. The magnetic unit cell is found to be the same as the chemical unit cell. The magnetic moments order parallel with each other along the b -axis. The magnetic structure in the a c plane is such that a Gd1 moment is ordered antiparallel to the nearest neighboring Gd1 moments and is coupled parallel to the next-nearest neighboring Gd1 moments. The Gd2 moment is coupled antiparallel to the nearest neighboring Gd1 moment. The temperature dependence of the order parameter is extracted and is found to be explained rather well by the result of an S = 7/2 molecular field approximation. The collinear structure of the magnetic moments in the triangular lattice and the absence of large magnetic fluctuations around the magnetic transition temperature s...

Non-resonant X-ray Bragg diffraction measurements on a small, single crystal of α-Gd 2 S 3 in zero and non zero applied magnetic fields are reported. From independent neutron diffraction measurements, the magnetic unit cell is found to be the same as the chemical unit cell. Therefore, the observation of magnetic X-ray diffraction by this compound is particularly challenging. We observe a change in the intensity around the Neel temperature in zero field, as well as around the phase boundaries at finite magnetic fields. The X-ray diffraction intensity is calculated based on the previously established magnetic structure. A reasonable amount of intensity from the interference between magnetic and charge scattering is predicted, and it provides a satisfactory account of our observations.

Results of non-resonant X-ray Bragg diffraction by CeB6 are reported. This material has been described in terms of a simple antiferro-quadrupolar order below TQ = 3.2 K. We determine for the first time, directly and quantitatively the orbital ordering in this material. In particular, we find direct evidence for a simultaneous ordering of a quadrupole (QP) and a hexadecapole (HDP) moments below TQ. From a strong dependence of the Bragg intensity on applied magnetic field in phase II, we conclude that octupole (OP) moments are induced and are coupled to the QP and HDP moments. When spontaneous magnetic dipole order sets in below TN = 2.4 K (phase III), a large enhancement of the Bragg intensity confirms the coupling between the dipole and the QP, OP and HDP moments.

Magnetic susceptibility, magnetization and heat capacity measurements are performed on a single crystal sample of α-Gd 2 S 3 . From the heat capacity measurements, we find a sharp anomaly at ≃10 K ...

Synchrotron X-ray diffraction measurements on a spin–Peierls material CuGeO 3 in applied magnetic fields, H , up to 15 T are made. We find that the temperature, T , dependence of the incommensurate Bragg peak at a lower H is quite different from that at a higher H . At sufficiently high fields, we find that the lattice incommensurability, δ l , is almost independent of T , while at H slightly above the critical field = 12.25 T for the commensurate to incommensurate transition, δ l decreases with increasing T . We interpret that this finding is due to a stabilization of the incommensurate state by a strong magnetic field which suppresses thermal fluctuations.

Non-resonant X-ray diffraction measurements have been made on a dense Kondo material CeB 6 . A series of (n, n, n) reflections with n =half integers has been observed in phase III of this compound. The magnetic field dependence of these reflections at 1.6 K as well as the temperature dependence in zero field have been measured. The intensity of these reflections shows anomaly at the phase boundaries determined by Effantin and coworkers. From these experimental observations, we argue that the (n, n, n) reflections reflect an antiferro-quadrupolar(AFQ) ordering and AFQ moments are coupled to the magnetic dipole and/or octupole moments.

We have observed superlattice reflections from the low-carrier system CeP under high pressures up to 2 GPa and also under magnetic field up to 12.5 T by means of synchrotron X-ray diffraction. The observed intensities of superlattice reflections are well explained by a model that takes into account both the lattice and charge modulation due to the periodic arrangement of ferromagnetic double layers of Γ8-like Ce ions in the lattice of Γ7 Ce ions. A new magnetic phase with the period of nine Ce planes was found in the experiment at the magnetic field of 12.5 T.

The results of non-resonant magnetic x-ray diffraction measurements of the metamagnet FeCl2·2H2O subjected to an applied magnetic field, H, are reported. The material shows two successive first-order phase transitions: at Hc1 = 3.62 T from the antiferromagnetic (AF) to intermediate (I) phases, and at Hc2 = 4.67 T from phase I to a ferromagnetic phase at low temperatures. We find that the AF and I phases coexist over a wide range of H below Hc1, when H is decreased from the I phase. We were able to follow the evolution of the AF and I domains with the change of H. The coexistence appears not to come from demagnetizing effects, and instead reflects the intrinsic nature of the material.

Inelastic neutron scattering experiments on Dy11B2C2 and Dy0.07Y0.9311B2C2 have been performed. The results enable us to infer important properties of the crystal-field levels of Dy3+ in DyB2C2 which has fascinating structural and magnetic properties that are attributed to the electronic states of the Dy ion. While no clear excitation was observed in pure DyB2C2, three excitations from the ground state with the energies 1.4, 4.1 and 5.8 meV were observed in Dy0.07Y0.9311B2C2. By comparing the present results with the previous crystal-field calculation, we infer that the ground state of Dy3+ in YB2C2 is Γ8 which is split into two Kramers doublets by the tetragonal potential. Additionally, the heat capacity measured on the diluted system is compared with a calculation using the low part of the energy level scheme obtained from the neutron experiments. Good agreement between theory and experiment is obtained.

The magnetic structures of an Er (90 A)/Tb (10 A) superlattice with the c-axis of the hcp structure parallel to the growth direction are investigated by neutron diffraction. As a function of temperature, the magnetic component parallel to the c-axis undergoes the same sequence including the Neel and Curie temperatures as bulk Er, while the component in the basal plane retains a helical ordering at higher temperatures up to 130 K, which is more than twice the corresponding temperature of bulk Er. We argue that the basal-plane ferromagnetic ordering of the adjacent Tb layers has enhanced the development of the basal-plane ordering in the Er layers.

Specific heat and Faraday rotation magnetometry were used to determine the axial magnetic phase diagram of the dilute hexagonal antiferromagnet Fe0.85Mg0.15Br2. In contrast to metamagnetic pure FeBr2, the first-order line of transverse phase transitions, H1(T), is disconnected with the antiferro-to-paramagnetic phase line Hc(T) and extends down to Ht = 0 at Tt ≈ 8.7 K. This is attributed to symmetric off-diagonal exchange in the presence of structural disorder. Moreover, a spin-flop phase emerges beyond Hc(T) up to a bicritical point (Tb ≈ 9.3 K, μ0Hb ≈ 1.3 T).

Using a pulsed neutron source we have been able to observe inelastic signals at high energies from the ladders of ${\mathrm{La}}_{6}{\mathrm{Ca}}_{8}{\mathrm{Cu}}_{24}{\mathrm{O}}_{41}.$ These signals constitute the magnon branch $(\ensuremath{\sim}30l~El~\ensuremath{\sim}190$ meV) for the lowest triplet excitation. A fit to a theory including a coupling along the leg ${(J}_{leg})$ and rung ${(J}_{\mathrm{rung}})$ alone gives the value ${J}_{leg}{/J}_{\mathrm{rung}}\ensuremath{\sim}2$ that is not consistent with expectations from a geometrical consideration and the exact diagonalization calculation. This inconsistency is removed when our data are fitted with ${J}_{leg}{=J}_{\mathrm{rung}}=110$ meV and a four-spin exchange interaction, ${J}_{\mathrm{ring}}=16.5$ meV.

The effect of dimethylarsinic acid (DMA) on skin tumorigenesis by UVB irradiation was examined. Hairless mice (Hos: HR-1) irradiated with UVB at a dose of 2 kJ/m 2 twice weekly, were fed with drinking water containing 1000 ppm DMA, a main metabolite of inorganic arsenics, produced more skin tumors than DMA-untreated mice. Histopathological examination revealed that the mouse malignant tumors with severe atypism appeared only in the treatment group of UVB plus 1000 ppm DMA. These positive results point out the importance of dimethylated metabolites of inorganic arsenic in the process of skin carcinogenesis.

Effects of Zn impurities on a spin-ladder material Na 2 Co 2 ( C 2 O 4 ) 3 ( H 2 O ) 2 are reported. We measured the magnetic susceptibility, χ on a single crystal and find that χ at a high field shows a broad peak at about 20 K and a Curie-tail at low temperatures. We interpret the low temperature Curie-tail as due to an induced moment around Zn impurities. At a low field, we find a spin-glass behavior evidenced by a difference in χ for field cooled and zero field cooled measurements. We present a possible mechanism for the appearance of this spin glass.

The compound (CH 3 ) 2 CHNH 3 CuCl 3 has recently been found to be an ideal ferromagnetic-antiferromagnetic alternating Heisenberg chain with the energy gap Δ/ k =17∼18 K [H. Manaka et al. : J. Phys. Soc. Jpn. 66 (1997) 564]. When an external field H is applied to this compound, the energy gap should vanish at the critical field H c1 = Δ/ g µ B . Just above H c1 , the three-dimensional magnetic long-range order is expected, if the interchain coupling exists. Motivated by this expectation, we performed specific heat measurements over a temperature range from 0.5 to 5 K applying H up to 12 T. As a result, we found a λ-type anomaly of specific heat over 10∼12 T, which indicates a transition to the three-dimensional long range order. The temperature at which the λ-type anomaly appears increases with increasing H . The critical field obtained by extrapolating the curve of the λ peak position versus H is 9.0 T, which is close to that obtained from a magnetization measurement.

From a heat capacity ( ${C}_{p}$) measurement on a single crystal sample of the $S\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}1$ quasi-one-dimensional (Q1D) Heisenberg antiferromagnet (HAF) $\mathrm{Ni}({\mathrm{C}}_{5}{\mathrm{H}}_{14}{\mathrm{N}}_{2}{)}_{2}{\mathrm{N}}_{3}({\mathrm{PF}}_{6})$ in applied magnetic fields, we found an anomaly which is indicative of a magnetic long-range ordering. We were able to follow how the position of the anomaly in ${C}_{p}$ changes with temperature $(T)$ and magnetic field ( $H$). An experimental $H\ensuremath{-}T$ phase diagram of an $S\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}1$ Q1D HAF is obtained and compared with that of the corresponding classical system.

Er thin films with thicknesses ranging from 88 to 196 A and with their c-axis perpendicular to the film plane were prepared on the Nb buffer layer deposited on substrate. The magnetic phase transition temperatures showed periodic change as a function of Er thickness with a period of 20 A, which corresponds to about seven atomic layers of Er. The periodic change in the magnetic property was found to be accompanied by that in the c-axis lattice constant. A possible origin of the periodic changes is discussed.

We have performed magnetization measurements up to 55 T on Sr 14 Cu 24 O 41 which has simple chains and ladders of copper ions. The magnetization curve is reasonably fitted with a theory based on an isolated dimer model with a remarkably small number of spins. The result is discussed in comparison with those of ESR and neutron scattering measurements.

Finite-size effects in a spin-$1/2$ one-dimensional (1D) Heisenberg antiferromagnet (HAF) are studied experimentally and theoretically. The calculated susceptibility is compared with that observed in the quasi-1D HAF ${\mathrm{SrCu}}_{1\ensuremath{-}x}{\mathrm{Mg}}_{x}{\mathrm{O}}_{2}$. Excellent agreement between theory and experiment is obtained without any adjustable parameters above about $0.02J$, where $J$ is the dominant exchange interaction constant.

Neutron-scattering measurements have been performed on the S= (1) /(2) quasi-one-dimensional system Sr{sub 14{minus}x}Y{sub x}Cu{sub 24}O{sub 41}, which has both simple chains and two-leg ladders of copper ions. We observed that when a small amount of yttrium is substituted for strontium, which is expected to reduce the number of holes, the dimerized state and the structure in the chain are changed drastically. The inelastic peaks originating from the dimerized state of the chain become broader in energy but not in momentum space. This implies that the dimerized state becomes unstable but the spin correlations are unchanged with yttrium substitution. Furthermore, it was observed that nuclear-Bragg-peak intensities originating from the chain show strong temperature and x dependence, which suggests that the chains slide along the c axis as temperature and x are varied. {copyright} {ital 1997} {ital The American Physical Society}

Neutron-scattering experiments have been performed on the metamagnet ${\mathrm{FeBr}}_{2}$ under external magnetic fields. We find an anomaly in the temperature (T) and magnetic-field (H) dependences of the intensity of the (2,0,1/2) antiferromagnetic Bragg scattering at the temperature ${\mathrm{T}}_{1}$(H) at which an anomaly in specific heat has been observed in addition to the anomaly at the N\'eel temperature ${\mathrm{T}}_{\mathrm{N}}$(H). We argue that our results are consistent with the theoretical H-T phase diagram of a metamagnet in which the tricritical point decomposes into a critical end point and a bicritical end point. We locate the latter point at ${\mathrm{T}}_{\mathrm{cr}}$\ensuremath{\cong}10.8 K and ${\mathrm{H}}_{\mathrm{cr}}$\ensuremath{\cong}1.4 T in this compound.

We have studied the magnetic properties of the S=(1)/(2) quasi-one-dimensional Heisenberg antiferromagnet SrCuO{sub 2}, which has zigzag chains of Cu{sup 2+} ions. We have observed a static magnetic ordering below T{sub c}{approximately}2 K. The weak internal field in the muon spin relaxation spectra and the absence of the magnetic Bragg peaks below T{sub c} suggest that the Cu{sup 2+} moments are largely reduced probably due to the quantum fluctuation. The remarkable suppression of the ordering temperature (kT{sub c}/J{sub 2}=1.1{times}10{sup {minus}3}), where J{sub 2} is the dominant exchange constant, probably originates from the combined effects of quantum fluctuation and frustration. {copyright} {ital 1997} {ital The American Physical Society}

One-dimensional (1d) magnets show novel phenomena that originate from quantum effects. In some of the 1D antiferromagnet the ground state is a singlet and there is an energy gap to the excited state. These include an antiferromagnet with a spontaneously dimerized state originating from a competing interaction, and spin-Peierls materials. When a Spin Peierls system is doped with impurities, a long-range antiferromagnet ordering appears. Spin Ladders show quite different magnetic properties depending on the number of legs. When holes are introduced in a ladder, they can be superconductive.

Superlattices of Er 100−x Tb x Y (x=3.5) have been grown on Niobium buffer layers using molecular-beam-epitaxy method to investigate the magnetic properties of ErTb alloy layers. The temperature dependence of magnetization was measured using a SQUID magnetometer. A marked difference in the magnetization is found between the superlattices with thicknesses of 35 A and 105 A. The result is discussed in conjunction with the spin structure determined by neutron scattering studies.

From a heat capacity measurement in high magnetic fields and at low temperatures, we have obtained evidence for a magnetic ordering in the S = 1 quasi-one dimensional Heisenberg antiferromagnet . The transition temperature is at 12 T parallel to the chain axis.

We have performed an X-ray scattering experiment on the Kondo-lattice compound Ce ( Ru 1 - x Rh x ) 2 Si 2 , which shows an incommensurate spin density wave (IC-SDW) in the Rh-concentration range 0.03 x 0.35 . We have discovered charge scattering due to the charge density wave (CDW) with a wave vector 2 Q , where Q = ( 0 0 q ) is the wave vector of IC-SDW. This is the first observation of the CDW associated with the IC-SDW in Kondo-lattice compounds.

Inelastic neutron scattering measurements have been performed on the S=1/2 quasi-one-dimensional system Sr14Cu24O41, which has both simple chains and two-leg ladders of copper ions. We have observed that both the chain and the ladder exhibit a spin gap, which originate from a dimerized state.

Specific-heat measurements have been performed on the Ising antiferromagnet Fe${\mathrm{Br}}_{2}$ in external magnetic fields. The temperature dependence of the magnetic specific heat shows two anomalies in external fields below the metamagnetic transition field. The anomaly at a higher temperature indicates the phase transition from the paramagnetic to antiferromagnetic phase. The lower-temperature anomaly shows up in the form of a peak superposed on a broad shoulder. The peak becomes sharp with the increase of magnetic field up to 2.9 T, which shows the existence of a new phase under a magnetic field. A theoretical analysis based on the pair approximation and Monte Carlo simulations reproduces the peak at the higher temperature and the broad shoulder. The broad shoulder appears as a result of competition between the nearest-neighbor ferromagnetic and the next-nearest-neighbor antiferromagnetic interactions in the triangular Fe lattice planes.

The oxalate-bridged complex {NPr4[MnCr(ox)3]}x (1) was prepared and its magnetic properties were studied, where NPr4 + = tetra(n- propyl)ammonium ion, ox2- = oxalate ion. X-ray powder pattern measurements suggested that the distance between the layers consisting of alternate array of Mn2+ and Cr3+ through ox2- ligands is shorter in 1 than {NBu4[MnCr(ox)3]}x(2) (NBu4 + = tetra(n-butyl)ammonium ion). The magnetic transition temperature of 1 (T c = 6.3±0.2 K) determined from ac magnetic measurements was, however, almost the same as the T c reported for 2. In contrast with the case of 2, compound 1 showed a normal magnetization curve which saturates rapidly with the increase of magnetic field (below 10 kG).

This paper deals with a new method for optimal control of pneumatic cylinders with a disturbance observer. The pneumatic cylinder has been used as an industrial actuator, because it is simple, small and economic. The PID or I-PD controller is used for position control of the cylinder, because its performance is excellent. However it is difficult to decide precisely the position of piston rod, owing to air compression and friction of the device itself. Furthermore, the dynamic response of these controllers depend on their control gains. Therefore these gains should be adjusted properly when the controlled object is changed. So, we consider the variation of the controlled object as a disturbance, and try to make compensation for its inference. We compose a better robust system from the disturbance observer with LQI controller. The experimental result shows that the proposed method has a better performance than the conventional LQI controller.

Dc, linear ac and nonlinear ac susceptibility measurements on a nominally pure single crystal of the S=1 linear chain Heisenberg antiferromagnet Ni(C 2 H 8 N 2 ) 2 NO 2 ClO 4 (NENP) show clearly that a spin-glass transition takes place in this sample. A possible origin of this spin-glass freezing is discussed.

This paper describes a new method for the model reference I-PD controller using neural networks. I-PD controllers are being widely used because of their excellent performance. However, an effective method for determining I-PD gains has yet to be developed. In this paper, we have come up with an auto-tuning method for the I-PD controller using neural networks. This method deals with coupling coefficients of the networks as I-PD gains of the I-PD controller. The coupling coefficients are adjusted using a back-propagation algorithm so as to minimize the error between the controlled object and reference model outputs. The experiments conducted show that this method is effective in controlling the position of pneumatic cylinder.

Antiferromagnetic resonance (AFMR) experiments on a single-crystal sample of Rb2MnCl4 have been performed using a spectrometer with wide frequency and magnetic field ranges. All the AFMR modes predicted for a uniaxial antiferromagnet have been observed. We find a significant contribution of the non-linear term in the expression of the AFMR frequency to the temperature dependence of the resonance point in the high-field low-frequency region.

We have measured the valence-band photoelectron spectra of (La 1- x Sr x ) 2 CuO 4-δ single crystals. Spectra obtained at low temperatures (30–80 K) are similar to each other as well as the results reported so far: The intensity at the Fermi level is quite low and the valence-band maximum is shifted to higher binding-energy than what the energy-band calculation predicts. At room temperature the intensity of the 3 eV band is reduced rapidly while the specimen is kept in dark, while it shows a quick recovery when the specimen is exposed to the excitation light for photoelectron measurements. This suggests that a photo-assisted process may take part in this phenomenon. Some possible mechanisms for the photo-induced changes are discussed.

The phase transition of ${\text{FeI}}_{2}$ is revisited. This material has the hexagonal crystal structure and shows an antiferromagnetic order at ${T}_{\text{N}}=9.3\text{ }\text{K}$ in zero field. When an external magnetic field is applied along the $c$ axis below ${T}_{\text{N}}$, successive metamagnetic transitions occur. The magnetism of ${\text{FeI}}_{2}$ has been interpreted based on the further neighbor interaction model on the triangular net. However, the exchange interaction constants derived from the analysis do not seem realistic. We have measured the magnetic susceptibility, magnetization, and specific heat on single crystals of ${\text{FeI}}_{2}$. From the specific-heat measurement, the temperature versus magnetic field phase diagram is constructed, in which five distinct magnetic phases, namely, the antiferromagnetic and four ferrimagnetic ones, exist. The magnetization measurement reveals that magnetization steps appear at $\frac{1}{3}$, $\frac{12}{25}$, $\frac{13}{25}$ and between $\frac{16}{25}$ and $\frac{17}{25}$ of the saturation magnetization, ${M}_{\text{s}}=3.5\text{ }{\ensuremath{\mu}}_{\text{B}}/\text{Fe}$. Based on an experimental evidence, we argue that a lattice distortion occurs below ${T}_{\text{N}}$ and the exchange interaction between spins on a triangle becomes anisotropic. We discuss the phase transition using the anisotropic triangular lattice model with ${J}_{1}$, ${J}_{2}$, and ${J}_{3}$. From the analysis of the metamagnetic transition fields, we obtain, $2.5l{J}_{1}/{k}_{\text{B}}l3.0\text{ }\text{K}$, $\ensuremath{-}16.2l{J}_{2}/{k}_{\text{B}}l\ensuremath{-}15.2\text{ }\text{K}$, and $\ensuremath{-}16.4l{J}_{3}/{k}_{\text{B}}l\ensuremath{-}14.4\text{ }\text{K}$.